WO1986001391A1

WO1986001391A1 - Brain electrical activity analysis and topographical mapping

Info

Publication number: WO1986001391A1
Application number: PCT/US1985/001655
Authority: WO
Inventors: Gil Raviv; Gabriel Raviv
Original assignee: Bio-Logic Systems Corporation
Priority date: 1984-08-31
Filing date: 1985-08-29
Publication date: 1986-03-13
Also published as: AU4776785A; EP0199739A1

Abstract

A method and apparatus for displaying a topographical map (Fig. 5A) of brain electrical activity of a patient. Input activity signals (14 in Fig. 1A) from the brain of a patient are sensed and evaluated (40 in Fig. 1A) by the apparatus responsive to computer software programs (stored at 29 or 53 in Fig. 1A). The sensed signals undergo line-by-line interpolation (Fig. 3) and are processed to generate video output signals (47 in Fig. 1A) of topographical maps (Fig. 5A) characteristic of brain electrical activity. The apparatus can also be operated at a central site remote from the location where the signals are measured on patients, and the computer software can selectively be downloaded from a remote source for data analysis.

Description

BRAIN ELECTRICAL ACTIVITY ANALYSIS AND TOPOGRAPHICAL MAPPING

The present invention relates generally to an apparatus and method for displaying a topographical map of brain electrical activity of a patient. More particu¬ larly the invention relates to a novel method and appara¬ tus for performing manipulation and analysis of data responsive to computer software for providing line-by¬ line interpolation of input activity signals and for processing the measured signals. The processed signals are output to provide a plurality of topographical maps in a variety of useful forms and including information characteristic of brain electrical activity. The appara¬ tus can also be operated at a central location remote from locations where the signals are measured on patients, and the computer software can selectively be downloaded from a remote source for analysis of the data.

Information on brain electrical activity is typically obtained by performing evoked potential (EP) response measurements and electroencephelogram (EEG) measurements. Such measurements often yield a set of complicated time varying outputs. A detailed and thor¬ ough analysis of these complicated outputs requires com¬ puter manipulation to determine differences of brain electrical activity of a selected patient compared to a representative normal population. A number of limitations currently exist for computer manipulation and analysis of these brain electrical activity measurements. In prior computerized apparatus the brain electrical activity measurements have been performed using a large number of system components to carry out the tasks of measurement, analysis and display of data. Furthermore, such appara¬ tus has taken the form of a dedicated, complete system with an extensive collection of computer software for a thorough analysis by the user. Consequently, such com¬ puterized systems are costly to purchase and maintain and are difficult to -service. Prior computerized systems for measurement and output of brain electrical activity also generate the topographical maps without clearly associat¬ ing all the appropriate data and without manipulating and displaying the optimum available data. For examples of various prior approaches, see, U.S. Patent Nos. 4,408,616; 4,417,591; 4,201,224 and 4,421,122; which are incorporated by reference herein. Therefore, in order to obtain the maximum benefit and understanding from the measured brain electrical activity, it is essential to manipulate, use and display the data to the viewer in the best manner possible. It is also desirable to be able to perform analysis and output of the necessary data without requiring a dedicated system at every measurement loca¬ tion.

Brief Summary of the Invention One of the primary objects of the invention is to provide an improved apparatus and method for- analyzing brain electrical activity and displaying a topographical map of brain electrical activity.

A more particular object of the invention is to provide a novel apparatus and a method for manipulating brain electrical activity signals using computer software to provide a video display of topographical maps of brain electrical activity.

Another object of the invention is to provide a novel method and apparatus for generating a video display of brain electrical activity signals interpolated and output for display on a line-by-line basis for positions between, as well as at, the electrode sensors on a patient's head. An additional object of the invention is to provide an improved method and apparatus for displaying a topographical map of brain electrical activity signals and including in the display a fixed color code scale wherein each color in the topographical map has a rela- tive value determined by correlation with each color in the fixed color scale.

Another object of the invention is to provide a method and apparatus for simultaneously displaying a plurality of topographical maps of different selectable states of brain electrical activity signals.

A further object of the invention is to provide an improved method and apparatus for increasing the rate of display of topographical maps of brain electrical activity signals by interlacing the output to the display memory of every other pixel line in each of the topo¬ graphical maps of brain electrical activity. A further object of the invention is to provide an improved apparatus and method for displaying topo¬ graphical maps of brain electrical activity signals meas¬ ured by electrode sensors on a patient's head at a remote location and carrying out the processing, analysis and output of the signals at one or more other locations.

Another object of the invention is to provide an improved method and apparatus for actuating measure¬ ment and analysis of brain electrical activity signals upon attaining a predetermined threshold condition for the incoming signals.

A further object of the invention is to provide an improved method and apparatus for performing cognitive testing using only a single period of data acquisition by intermixing various types of stimuli and sorting the associated EP responses by means of a computer.

An additional object of the invention is to provide an improved method and apparatus for performing a montage analysis using a single set of measurements stored in a memory to identify the location and nature of selected features of interest in topographical maps of brain electrical activity.

A further object of the invention is to provide an improved method and apparatus for evaluating noise signals and for generating a substantially noise-free output of brain electrical activity signals by applying an appropriate digital filter to the activity signals.

In accordance with the invention an apparatus and method for measuring and displaying topographical maps of brain electrical activity signals uses various selectable computer software programs to process and analyze the measured signals, to generate interpolated outputs of the brain electrical activity signals, to carry out additional analysis and then output the results to a display processing unit.

A user can select for display a plurality of the topographical maps which illustrate various charac¬ teristics of brain electrical activity signals, such as evoked potential (EP) response information and electro- encephelogram (EEG) information. The brain electrical activity is measured by electrode sensors which generate input activity signals. These input activity signals are interpolated line-by-line to generate an expanded finer matrix of interpolated values. Interpolation is selec¬ tively performed every other pixel line in the interlace mode of constructing the topographical map. The display of characteristic data includes a color code scale and associated numerical values for determining the relative magnitudes of regions of the topographical map. In addi¬ tion to the topographical maps, individual characteristic waveforms and other associated parameters can be simul¬ taneously output to a video display or printer for com¬ parison and association with the topographical maps. The apparatus also operates responsive to selected software programs which are directed to the following areas: (1) removal of unwanted noise signals from the measured signals, (2) performance of montage analysis to identify by an iterative procedure particular features of interest in the measured signals, (3) perfor¬ mance of threshold activation analysis wherein the incom¬ ing signals are not measured and analyzed until a pre¬ determined threshold condition has been achieved, (4) performance of a cognitive testing routine in a single testing period by applying a plurality of stimuli and sorting the associated responses with a computer, (5) performance of a Fourier transformation of EEG signals to determine frequency energy band output for the major frequency bands, and (6) performance of integration anal_¬ ysis of EP responses to present an averaged sum of re_¬ sponse amplitudes to enable the user to isolate the most significant spatial and time segment contributions to the EP response and to condense the EP response spectrum to a few succinct topographical maps. Other simple mathema¬ tical operations such as first and second order differen¬ tials and arithmetic differences of the signal also enable characterization of the patient response and allow comparison with normal population responses to isolate abnormal responses for clinical diagnostic purposes. The apparatus also can utilize external means for processing, analyzing and output of the topographical maps at a loca¬ tion removed from the locations at which signals are measured by remote means, such as electrode sensors.

Further objects and advantages of the present invention, together with the organization and manner of operation thereof, will become apparent from the follow¬ ing detailed description of the invention when taken in conjunction with the accompanying drawings wherein like reference numerals designate like elements throughout the several views.

Brief Description of the Drawings FIGURE 1A is a block diagram of an apparatus for measuring brain electrical activity signals and for displaying topographic maps characteristic thereof, and FIGURE 1B is a functional block diagram showing the flow through the apparatus of the measured input activity signals; FIGURE 2 shows a top view of positions of an electrode sensor arrangement with respect to a patient head outline;

FIGURE 3 is an array of electrode sensors and a superimposed image of a line-by-line interpolation of signals for the array;

FIGURES 4A and 4B are block diagrams of two alternative methods for line-by-line interpolation and output of signals;

FIGURE 5 is a display output of evoked poten¬ tial (EP) response measurements showing a topographical map, associated waveforms for selected electrode sensor locations and a vertically positioned color code scale;

FIGURE 6 is a block diagram of a noise signal evaluation procedure; and

FIGURE 7 is a display output of a plurality of topographical maps of evoked potential (EP) response measurements integrated over the time intervals shown.

Description of Preferred Embodiments Referring now to the drawings, and in particu¬ lar to FIG. 1A, a block diagram of a brain electrical activity mapping apparatus constructed in accordance with one embodiment of the present invention is indicated generally at 10. The brain electrical activity mapping apparatus (hereinafter referred to as the apparatus 10) includes sensor means, such as, for example, a set of electrode sensors 12 (for example, Grass gold cup manu- factured by Grass Corporation) arranged on the top of a patient's head 13- In FIG. 2 is shown an enlarged detail of a preferred .arrangement for a rectangular array or matrix of twenty-one of the electrode sensors 12 posi¬ tioned on the patient's head 13. The arrangement illus- trates one acceptable variety selected from various con¬ ventional international formats. In response to brain electrical activity the electrode sensors 12 generate input activity signals 14. In alternate forms of the invention remote means, such as the sensors 12, are located at remote sites as part of a distributed system for performing measurements of brain electrical activity data, such as the signals 14. These remote measurements can be communicated through remote apparatus, such as interface devices coupled to modems, to a central loca- tion for analysis by the remainder of the apparatus 10 described hereinbelow.

In selected operating modes of the apparatus 10, such as in measurement of evoked potential (herein¬ after "EP") response, a stimulus 16 is also applied to the patient, and in response to the stimulus 16 the re¬ sulting brain electrical activity is sensed by the elec- trode sensors 12. A detailed discussion of EP response measurements is set forth in Duffy et al., "Brain Elec¬ trical Activity Mapping (BEAM): A Method for Extending the Clinical Utility of EEG and Evoked Potential Data," Annals of Neurology 5__t Apr., 1979, pp. 209-231; which is incorporated by reference herein. The type of stimulus 16 used in EP response measurements is, for example, a strobe light, a sound (such as a click generator) or a somatosensory stimulus, such as mild electrical shock. These stimuli 16 can be periodic, aperiodic and can also be combinations of each available type of the stimulus 16. In the illustrated embodiment of FIG. 1A, the stimu¬ lus 16 is controlled responsive to a control signal 18 from a main computer, such as a microcomputer unit 22. The type of stimulus 16 is selected by a user input, such as a keyboard 23. In alternative forms of the invention, the stimulus 16 is provided responsive to a stimulus controller 20 which is a separate microcomputer or is a remote control source.

In other modes of operation of the apparatus ιo, such as in electroencephelogram (hereinafter "EEG") measurements, the stimulus 16 is not applied to ^• the patient. However, the measurement of brain electrical activity in the EEG mode otherwise follows substantially the same steps as for EP measurement. Therefore, in general as shown in FIG. 1A, the sensed input activity signal 14 is output from the electrode sensors 12 to processing means which includes an analog multiplexer 24, an amplifier 26 and an analog to digital converter (A/D) 28. If a Grass or Beckman polygraph is used, the elec- trode sensors 12, the multiplexer 24 and the amplifier 26 are included in the polygraph.

In the illustrated embodiment the amplifier 26 comprises a plurality of twenty-one amplifiers, each connected to an associated one of the electrode sensors 12. The multiplexer 24 accepts from the amplifier 26 each of the amplified input activity signals 14, and outputs each of these input activity signals 14 in serial fashion to the A/D converter 28 (for example, a Dual Systems AIM 12). The A/D converter 28 provides to the microcomputer unit 22 an amplified and digitized, or a converted, form of the input activity signal 14. In general, processing means includes those components of the apparatus 10 which operate on the signals output by the electrode sensors 12 to provide the amplified and digitized form of the input activity signals 14. In some forms of the invention, such as during measurement of EEG brain electrical activity, the processing means is also combined with the sensors 12 to form a remote sensor means (for example, a commercial polygraph) at a location remote from the remainder of the apparatus 10. In the manner discussed hereinbefore, the data from the poly¬ graph is then communicated by a modem to the centrally located remainder of the apparatus 10 which analyzes the data to provide an output for display.

The microcomputer unit 22 in FIG. 1A can be any one of a plurality of commercially available computers, such as, for example, a Zenith Z-100, which uses an 8088 central processor chip (see, Intel Component Data Catalog, Jan. 1982, pp. 8-25 to 8-51, which is incor¬ porated by reference herein). The Zenith Z-100 also includes the keyboard 23, a display processing unit (hereinafter "DPU") 39 which will be described in detail hereinafter, a disk drive (not shown) and on board random access memory (hereinafter "RAM") 30, and PROM and ROM (not shown) memories. The microcomputer unit 22 controls collection, manipulation and output of the input activity signals 14. In a preferred embodiment, the microcomputer unit 22 includes the RAM 30 which functions in part as an averaging means for storing at predetermined locations a running accumulation of the plurality of input activity signals 14. The microcomputer unit 22 adds each new incoming value for the signals 14 to the previous value and stores the total in the RAM 30 at the predetermined locations. This accumulation of the amplified and con¬ verted input activity signals 14 results in statistical averaging of the input activity signals 14 which improves the signal to noise ratio. Under typical operating con_¬ ditions one to ten minutes of data averaging is desirable to obtain statistically meaningful values for the input activity signals 14. In a preferred embodiment of the invention, the apparatus 10 controls data gathering and analysis respon¬ sive to software programs stored on a disk or tape 29, and the programs are read into the RAM 30 and executed by the microcomputer unit 22. The user interacts with the microcomputer unit 22 through input means to supply an input signal responsive to a user input. Examples of input means include the keyboard 23, a light pen 34 and a mouse 36. The user can also supply an input signal by transfer of information already stored on a disk storage unit 27 or stored in the disk or tape 29, or stored in a memory external to the apparatus 10, such as, for exam¬ ple, a remote computer memory (not shown). These various input means enable setting of variables such as the time period of data taking, the number and type of the stimuli 16 and the desired software programs to manipulate the data for output and display for user analyzation.

The operation of the apparatus 10 as illus¬ trated in FIG. 1A can be better understood by reference to the procedural and signal flow diagram of FIG. 1BA and 1BB. As illustrated in FIG. 1BA, the apparatus 10 in the first decisional block has been initialized with user selected parameters or default parameters, and a mode of operation is selected. If the EP response mode is selected, then a predefined stimuli 16 is applied to the patient as a first step. However, if the EEG mode is selected, then there is no externally applied predefined stimuli 16, and the electrode sensors 12 detect EEG sig¬ nals directly from the patient's head 13. In any event whether the signals originate from the patient as an EEG signal or as an EP response signal, the next step is directed to preprocessing the outputs from the electrode sensors 12. This preprocessing can include, for example, a number of steps, including amplification, hardware filtering, software filtering and fast Fourier transfor¬ mation.

The preprocessed outputs from the electrode sensors 12 are then digitized, and the digitized form of the signals 14 are placed in predefined locations in the RAM 30 corresponding to predefined sensor positions. The signals 14 corresponding to particular sensor positions can alternatively or additionally be stored in secondary storage, such as the disk storage unit 27 or the tape 29. Once the signals 14 have been digitized and stored in the.RAM 30, a determination is made whether the apparatus 10 is in the EEG or the EP mode. If operating in the EEG mode the procedure skips to step B shown in FIG. 1BB. If, however, the apparatus 10 is in the EP mode, the signals 14 are accumulated in the predefined locations in the RAM 30 and/or can be stored in the disk storage unit 27 or the tape 29. Operation of the appa¬ ratus 10 then proceeds to determine whether the selected number of signals 14 have been acquired in accordance with the initial setup parameters. If the selected num¬ ber of the signals 14 has been acquired in the appropri¬ ate manner, processing proceeds to step B which continues in FIG. 1BB. If, however, the selected number of the signals 14 has not been acquired, then processing resumes at the step of applying the predefined stimuli 16. This operation of the apparatus 10 in the EP mode shown in FIG. 1BA continues until the selected number of the sig¬ nals 14 have been acquired.

Referring to FIG. 1BB, the operation continues at step B from FIG. 1BA. At this point the RAM 30 con¬ tains data representative of the accumulation of the digitized signals 14 at predefined locations in the RAM 30 corresponding to respective sensor positions. Alter- natively at this point, accumulated data signals can be input from a secondary storage source, such as the disk storage unit 27, to the RAM 30 to provide the initial database from which further manipulation proceeds. The next step in the operation is the selection of one of a plurality of options as to how to operate on the signals 14. Once the option is selected, the apparatus 10 pro¬ ceeds to perform the appropriate operations on the sig¬ nals 14 as stored and accumulated in the RAM 30. These operations on the signals 14 can include, for example, attenuation or amplification, digital filtering, smooth¬ ing, fast Fourier transformation, differentiation, inte¬ gration and statistical data analysis. In other forms of the invention these operations can be performed prior to storage in the RAM 30, such as after the A/D conversion 28 and prior to initial storage in the RAM 30.

After the selected option has been performed, the result of the operation is stored again in the RAM 30, either at new locations or at the previous locations, such as by overwriting the previous locations with the new form of the signals 14. Alternatively or additional¬ ly, the results can be stored in a secondary storage such as the disk storage unit 27. At this point, the signals 14 stored in the RAM 30 provide the basis for interpola- tion, either line by line or in an interlaced or alter¬ nate line mode of output, and the interpolated form of the signals 14 is output in a display format compatible with the DPU 39. The DPU 39 therefore receives and stores the interpolated form of the signals 14 in the display RAM of the DPU 39, one line at a time, as shown in the next block of FIG. 1BB. The DPU 39 generates an image on a display means, such as a video display 43 (for example, a Zenith ZVM-133), or the image is output to another form of the display means, such as an ink jet printer 45 (for example, a TRS 80 CGP220 manufactured by Tandy Corp.). Interpolation

In the illustrated form of the invention, the input activity signals 14 stored in the RAM 30 undergo an interpolation within the RAM 30 under control of the microcomputer unit 22. An expanded matrix is formed of finer resolution (for example, a forty by forty array of points in the preferred embodiment) than the arrangement of the twenty-one electrode sensors 12. The general technique of interpolation using three points to form finer resolution frames of the input activity signals 14 is known (see, for example, Duffy et al., "Brain Elec¬ trical Activity Mapping" referred to hereinbefore). However, as will be discussed hereinafter, the present invention includes an improved interpolation method which uses a set of two points to generate and output line-by¬ line the interpolated form of the input activity signals 14.

In the preferred embodiment, a line is one line of pixels, wherein a pixel is the smallest picture ele- ment used to construct the video image. As will be de¬ scribed in more detail hereinafter, each pixel color is described completely by three bits of digital information stored in the RAM 30. In alternative forms of the inven¬ tion a color mapping procedure can be used to assign color values to the pixels. For example, each pixel can have five bits in the RAM 30 to describe one of thirty- two possible color choices which points to a color map also located in the RAM 30. The color map can have a preselected number of n bits of information which de- scribes each of 2ⁿ possible colors, and the color map digital description is output to the intensity digital to analog converter part of the DPU 39 for display of the desired pixel color.

Upon completion of the interpolation for a given line, the interpolated values can also be stored in a disk storage unit 27 for future use and analysis. A video output 37 of the interpolated input activity sig¬ nals 14 is output line-by-line to the DPU 39 (preferably contained within the microcomputer unit 22 as discussed hereinbefore) in preparation for output to the video display 43. The interpolated form of the signals 14 can also be output from the RAM 30 or the DPU 39 for hard copy printout on the printer 45 or for completion of an additional data analysis 40 before being displayed. These alternative operations will be discussed in more detail hereinafter.

In the illustrated embodiments of FIG. 3 and FIGS. 4A and 4B, the interpolation begins by generating amplitudes at four projected electrode sensors 31 at the corners of the matrix of the electrode sensors 12 to establish a rectangularly symmetric five by five matrix of the input activity signals 14. The values for the four signals 14 at the projected electrode sensors 31 are interpolated from a linear average projection from the intersecting perpendicular lines of the electrode sensors 12 which converge on each of the projected electrode sensors 31. Once the signals 14 have been established at each of the projected electrode sensors 31, the interpo¬ lation proceeds by selecting a first line, such as a line 33 in FIG. 3 along the perimeter of the matrix of the electrode sensors 12, and starting with line 33 the line- by-line interpolation is carried out parallel to the line 33.

The use of a commercial polygraph unit with, for example, twenty-one of the electrode sensors 12, rather than twenty-five actual sensors for the five by five matrix, enables use of a standard unit of substan- tially lower cost to the user. Further, the approximate¬ ly rectangular arrangement for the twenty-one electrode sensors 12 enables the interpolation procedure to be simplified. In one form of the invention described in FIG. 4B interpolation proceeds along lines which are parallel to one another and passes through the regular array of points defined by the rectangular arrangement of the electrode sensors 12. Therefore, the interpolation takes place along one-dimensional lines which are easily defined in the rectangular arrangement and interpolation calculations are performed more easily using only two points to generate a bracketed intermediate point. In prior conventional interpolation approaches, three points from a non-rectangular arrangement have been used (see, for example, U.S. Pat. No. 4,417,591, which is incor¬ porated by reference herein).

In a preferred form of the invention described in FIG. 4A, after determination of the signals 14 at the projected electrode sensors 31, the linear interpolation is carried out for selected points a predetermined frac¬ tion of the distance between each nearest neighbor pair of the signals 14 in a column 25 of the electrode sensors 12. An interpolated value for the selected point is determined by forming a linear weighted average of an appropriate pair of signals 14, such as the two input activity signals 14 at a pair of the electrode sensors 12. Alternatively, the pair is one of the signals 14 at one of the electrode sensors 12 and one of the projected sensors 31, which bracket the location of the selected point. For example, in the illustrated embodiment of FIG. 3 the distance between each of the electrode sensors 12 is divided into eight parts. Thus, if the selected point is one-eighth of the distance between a first one of the sensors 12 and a second one of the sensors 12, then the value for the electrical activity signal 14 at the interpolated point is seven-eighths the value of the signal 14 at the first sensor 12 plus one-eighth the value of the signal 14 at the second sensor 12. This interpolation procedure continues sequentially up each of the columns 25 of the electrode sensors 12 until the interpolation is complete for all five of the columns 25 which are perpendicular to the line 33. The interpola¬ tion is then performed for all remaining lines parallel to the line 33, proceeding incrementally from line 33 to line 35 and to the other lines until completion.

In another form of the invention shown in FIG. 4B, after the interpolation along the line 33 has been completed, the interpolation proceeds point by point for the line 35 and for each of the subsequent lines parallel to the line 33. This procedure is accomplished by first determining the signal 14 at the selected point which is a predetermined fraction of the distance between the electrode sensor 12 contained in the line 33 and the nearest electrode sensor 12 in the same column 25. This process is completed for only a first point in each of the five columns 25 of the electrode sensors 12_.. The resulting five points are shown in FIG. 3 as interpolated values 38 which lie at the intersections of the columns 25 and the line 35. These values 38 are then used to complete the interpolation along the line 35 in the same manner as described above for the embodiment of FIG. 4A. Interpolated values 41 are constructed from a linear weighted combination of the appropriate pair of the in¬ terpolated values 38 which bracket each of the values 41. The line 35 is then output for presentation on the video display 43. The outputted form of the signals 14 comprising the line 35 are therefore generated in a com¬ patible format for the conventional video display 43. Further details of operation of the video display 43 can be obtained by reference to the Zenith ZVM-133 operating manual, which is incorporated by reference herein. Al- ternatively, the line 35 is output for the additional data analysis 40 prior to display, depending on the user selected operational mode. Display of the complete frame of a topographical map 44 shown in FIGS. 5 and 7 con¬ tinues line-by-line, incrementally completing the inter- polation for each of a plurality of lines and outputting each of the lines to the video display 43.

These interpolation procedures enable the live time line-by-line processing of the input activity sig¬ nals 14 for output to the video display 43. The live time output and display of the signals 14 is accomplished without having to await formation of the entire video frame and also without having to store in the RAM 30 a plurality of the lines or a complete frame of the input activity signals 14 before output to the video display 43. Prior "live time" methods have required storage of the complete frame before the topographical map 44 could be displayed (see, for example, U.S. Pat. No. 4,417,591, which is incorporated by reference herein). Further, as mentioned hereinbefore, the present line-by-line inter¬ polation requires only two end points to perform the procedure, and this greatly simplifies the calculation and storage of values in the RAM 30 and decreases the calculation and display time.

In some forms of the invention, the input activity signals 14 undergo other operations prior to the data interpolation, such as the data analysis 40 (for example, data smoothing and a digital filtering treatment to be discussed in more detail hereinafter). Another example of the data analysis 40 is the performance of a Fourier transformation of the EEG form of the input activity signals 14 from the twenty-one electrode sensors 12. In order to avoid performing time consuming Fourier transformation for the larger number of values in the expanded frame containing the interpolated values 38 and 41, only the small numbers (twenty-one in the illustrated embodiment) of the unexpanded input activity signals 14 undergo Fourier transformation. Interpolation expansion to a finer matrix is generally done more efficiently on the data after completion of any extensive or complicated form of signal treatment, such as the Fourier transfor¬ mation operation.

Video Display In the preferred embodiment, after the interpo¬ lation and the optional data analysis 40 of the input activity signals 14, the resulting video output 37 is applied to the DPU 39 contained in the Zenith Z-100 unit. Alternatively, the raw input activity signals 14 accumulated in the RAM 30 can be output as a raw signal 25 by the microcomputer unit 22 to the DPU 39 without further processing, including interpolation. The video output 37 input to the DPU 39 is converted into an output signal 47 suitable for the video display 43 which pro_¬ vides the video presentation of the topographical map 44. In the preferred embodiment there is one dis- play rate, other than manually sequencing through the set of frames, for dynamic display of the change in EP re¬ sponse as a function of time elapsed after the stimulus 16 has been applied to the patient's head 13. The dis¬ play rate can also be increased by generating reduced sizes of the topographical maps 44, in a manner to be described in detail hereinafter. Operation of a typical form of the DPU 39 has been discussed hereinbefore in the Interpolation section and is also explained in, "Funda¬ mentals of Computer Graphics," J.D. Foley and A. Van Dam, Addison- esley Co., Reading, MA, 1982, pp. 112-136, which is incorporated by reference herein. Also, see U.S. Pat. Nos. 4,121,283, 4,139,838 and 4,213,189 which are incor¬ porated by reference herein.

In addition to the generation of the video display 43, as mentioned hereinbefore the interpolated input activity signals 14 are selectively stored in the disk storage unit 27 or applied to the ink jet printer 45 which provides a hard copy printout of the topographical map 44. The user selects print out of the topographical map 44 on the video display 43 by actuating transfer of the video output 47 to a page buffer 49 coupled to the ink jet printer 45. Upon filling the page buffer 49, the printer 45 outputs the hard copy printout.

In the illustrated embodiment of FIG. 5, the topographical map 44 is color coded, and in a preferred form of the invention thirty-two different color choices are used to encode the relative magnitude of the brain electrical activity for the input activity signals 14 displayed on the topographical map 44. In the illus- trated embodiment of FIGS. 1 and 5, color code means for encoding the colors on the topographical map 44 is accom¬ plished in conjunction with a software program which is read into the RAM 30 from the disk 29. The topographical map 44 is constructed of blocks of two by four, or eight, pixels; and as mentioned hereinbefore each of the pixels in the block are described by three separate storage bits, one for each of the memory locations in the RAM 30 associated with the red, green and blue colors which are used to construct all the colors. With three storage bits per pixel a total of two cubed, or eight, unique colors can be constructed. These eight colors, along with white, are assigned to individual pixels in the block and are mixed to generate twenty-four more colors. For example, the block of two by four pixels can be constructed in a predetermined manner using the unique colors to arrange the colors of near neighbor pixels around a selected given pixel to form a block having a light yellow appearance. This is acoo plished by having every next nearest neighbor pixel of the selected given pixel as a yellow pixel, which is described by the green storage bit as "1", and red bit as "0" and the blue bit as "1". The remaining nearest neighbor pixels around the given pixel are white with the red, green and blue stor¬ age bits all "1". Colors for the pixel blocks other than the unique colors are constructed in a similar fashion by mixing two preselected colors in the pixel blocks in the above described manner. This method of color construc- tion further helps to reduce the cost of the apparatus 10 which substantially enhances the commercial significance and usefulness of the apparatus 10.

In the illustrated embodiment the color coding of the topographical map 44 is graphically explained to the user by generating alongside the map 44 a vertically positioned, color column or scale 46 having different color segments 48. The thirty-two colors in the illus¬ trated embodiment are depicted by various cross hatching and line patterns. Each of the color segments 48 repre- sents a fixed relative magnitude within a selected closed data set of the interpolated values 38 and 41 for the input activity signals 14. A closed data set is meant to include those input activity signals 14 measured on the patient's head 13 for a fixed set of measurement vari¬ ables, such as, amplifier gain and the nature of the stimulus 16.

In alternative forms, of the invention, the color scale 46 is positioned horizontally or is arranged alongside selected portions of any number of sides (for example, four if rectangular) of the topographical map 44. The user can also select the display of only the color segments 48 which are being used for the associated topographical map 44. This enables removal of unused colors to simplify association of colors with an ampli¬ tude at a selected location on the topographical maps 44.

In the illustrated embodiment of FIG. 5 in addition to the topographical map 44 and the color scale 46, the video display 43 also includes waveforms 50 which are characteristic of the EP response input activity signal 14 at the user selected electrode sensors 12. The user also can display the waveforms 50 associated with the interpolated values 38 and 41. Each of the waveforms 50 is output and displayed as a color coded line and also is identified using a conventional international format with an appropriate letter and number (for example, CZ, 01 and F7 in FIG. 5). The letter and number are indica¬ tive of the selected electrode sensor 12 or other inter- polated point, such as one of the interpolated values 38 or 41.

In FIG. 5 are shown examples of the waveform 50 for EP response amplitudes which vary as a function of time above and below a centered zero base line. Typical- ly, the EP response is measured over time periods of 256, 512, 1024 or 2048 milliseconds. The topographical maps 44 appear to the viewer as a series of frames showing the outline of the patient's head 13. Each of the frames is characteristic of the EP response amplitudes at a par- ticular time after applying the stimulus 16 to the patient. For example, each frame can represent one par¬ ticular four millisecond time segment of the total set of the frames which covers the time period from zero to 512 milliseconds in four millisecond increments. Therefore, for each of the user selected locations on the patient's head 13 for one of the frames, there is displayed the associated waveform 50. A particular point on the wave- form 50 describes the amplitude for a particular time segment after the stimulus 16 has been applied to the patient. In order to pinpoint the time segment on the waveform 50, an indicator or a cursor 52 is displayed in FIG. 5 which points toward the time segment and to . the amplitude on the waveform 50.

In the display of the topographical maps 44 of the EEG input activity signals 14 the user is able to select one of the locations (such as, at one of the sen¬ sors 12 or the interpolated values 38 or 41) on the patient's head 13 and generate adjacent the EEG topo¬ graphical maps 44 an EEG curve of the contribution from the various frequency bands (i.e., α , B , <5 and θ ). The curve amplitude is correlated to an associated one of the frequency bands by using color coded segments posi- tioned along the abscissa, or frequency, axis of the EEG curve. The color coded segment is indicative of prese¬ lected ones of the frequency bands, such as the α,β,δ, and θ bands.

The user of the apparatus 10 also has the abil- ity to select the display of a plurality of reduced sizes of the topographical maps 44.- This feature enables the user to display a number of the topographical maps 44 on a single screen of the video display 43 or a single page of a printed output. For example, in FIG. 7 is illustra- ted the display of a plurality of the topographical maps 44, along with the color scale 46. In alternative forms of the invention the user also displays the waveforms 50 for the same or for different locations in each of the plurality of the topographical maps 44. The user can also select to display different brain electrical activity states or different types of measurements for the reduced size topographical maps 44. For example, the user can select the display of EP responses and EEG information or EP responses characteristic of a plurality of different ones of the stimuli 16.

COMPUTER SOFTWARE The apparatus 10 performs an analysis of the input activity signals 14 to provide the video output 37 responsive to various means, such as for example, com¬ puter means. In the illustrated embodiment of FIG. 1 the computer means comprises a computer software program selected by the user and the microcomputer unit 22 which executes the software program. In a preferred form of the invention shown in FIG. 1, the computer programs are stored on the disk or tape 29 and are loaded into the RAM 30 in preparation for execution by the microcomputer unit 22. In other forms of the invention, the computer pro- grams of the computer means are input from a remote ex¬ ternal source, such as a remote storage device (not shown) or a remote computer 53, into the RAM 30. Alter¬ natively the computer programs are input directly into the microcomputer unit 22 for execution therein. The ability to use the remote source for the computer pro¬ grams enables the user to draw on an extensive collection of software at a central location and helps reduce cap¬ ital costs for the small clinic or small group of prac¬ titioners. The means for providing the video output 37 also can generally include any form of logic means, hard¬ ware and software, which performs an analysis responsive to computer software programs to analyze the amplified and digitized input activity signals 14 to generate the video output 37. When the apparatus 10 processes data from a remote means, such as a remotely located polygraph or an electrode sensor 12 for sensing the signals 14, the sig¬ nals 14 are input to an interface means (not shown). This interface means translates the signals 14 to enable communication by a modem over a telephone line or other suitable telecommunications equipment to the processing means and to logic or computer means for analysis to generate the video output 37. Such a form of the appara_¬ tus 10 avoids the need to have a dedicated system and makes feasible the measurement of the signals 14 at re¬ mote locations and enables the use of the apparatus 10 by smaller clinics and individual practitioners who would otherwise be unable to support a dedicated system.

In the preferred embodiment, a master control program is provided as an executive which guides the user through the necessary steps for initial calibration of the apparatus 10, setting of apparatus parameters, in¬ cluding type of functions desired, topographical and Fourier transform data, filter characteristics, number of samples per second, display update frequency and so forth. The user calls up the executive program which then sequences the user through the appropriate command requests to provide for various functionality as de¬ scribed throughout this specification. The executive can be written in any plurality of languages, including as¬ sembly language, BASIC, FORTRAN, etc., and can operate under a plurality of commercially available operating systems, such as CP/M-86, MS-DOS or UNIX, on any of the plurality of commercial systems, such as the Zenith Z-100 system given as an example hereinbefore.

Once the apparatus 10 is calibrated and neces- sary set-up data is provided, the apparatus 10 can pro¬ vide the topographical map 44 of the brain electrical activity in either live time, as sampled data is being acquired and stored, or mapping and display of the brain electrical activity can be performed on prestored or transferred data files not actually gathered in live time and can even be performed at an external, remote location relative to the apparatus 10. The mapping and display operation can be performed by the apparatus 10 and/or electronic hardware processing of the input activity signals 14. Hard copy printout on the printer 45 and/or output to the video display 43 can be provided at the user's selection.

In another form of the invention instead of the master control program, the apparatus 10 can provide all necessary functions by providing a plurality of separate callable software routines for the user to call up at his option. In this case, no central executive program would be required.

The software programs are utilized in certain selected modes of measurement and analysis, while other programs are utilized in all modes of measurement and analysis of brain electrical activity. These computer software programs are explained in the subsections de¬ scribed hereinbelow:

Digital Filtering

The digital filtering program is one form of an analyzer means which more particularly acts as a filter means, such as a digital filter 54 shown in FIG. 1. In selected areas of biological science the concept of digi¬ tal filtering is a conventional method for removing or attenuating unwanted signals (see, for example, A.R. Moller, "Improving Brain Stem Auditory Evoked Potential Recordings by Digital Filtering," Ear and Hearing ___, 108- 113 (1983); and A.V. Oppenheim et al., Digital Signal Processing, chap. 5, Prentice-Hall, Englewood Cliffs, N.J. 1975; which are incorporated by reference herein). In the present invention the user is able to attenuate or substantially remove unwanted extraneous signals from the input activity signals 14 by applying a digitized filter function thereto. The digitized filter function is load¬ ed in the RAM 30 from the disk or tape 29 or from the remote computer 53. The digitized filter function is stored as attenuation (dB) in digitized form in the RAM 30 with an eight bit segment of the RAM 30 containing the attenuation value for one particular associated fre¬ quency. A complete frequency range for the digitized filter function is therefore embodied within a plurality of eight bit storage segments located in the RAM 30. More or less numbers of the segments can be utilized for more or less resolution of the frequency range. In performing the filtering operation the stored attenuation factors are applied to the stored amplitude at the asso¬ ciated frequencies to provide the reduced forms of the input activity signals 14. In a conventional system a hardware based fil¬ ter is usually applied before the signal 14 is digit¬ ized. Thus, the hardware filter is normally positioned immediately after the input activity signal 14 is output from the amplifier 26. However, in addition to attenuat- ing unwanted signals, there is also some attenuation outside the optimum frequency range due to an inherent lack of a sharp cutoff in the attenuation for the hard¬ ware based filters. Further, the conventional hardware filter causes shifts in signal phase which distort the shape and position of the input activity signals 14. The digital filter 54 is however programmable to have a sharp cutoff and not introduce signal phase shifts when applied to the input activity signal 14. Nevertheless, where appropriate filter characteristics are achievable, the hardware filter could be utilized.

In the preferred form of the invention, the apparatus 10 uses the digital filter 54 derived from computer system hardware and software of the apparatus 10. Digital filtering is provided by the digital filter 54 responsive to the input activity signal 14 for loca¬ tions after the accumulated averaged form of the signal 14 has been stored in the RAM 30, but before the interpo¬ lation has been performed. In other forms of the inven¬ tion, the digital filter 54 is applied immediately after the input activity signal 14 is output from the multi¬ plexer 24 (see FIG. 1) or after output from the A/D con¬ verter 28. Alternatively, the digital filter 54 is ap¬ plied after the interpolated form of the input activity signal 14 has been generated. In the illustrated embodiment, the digital filter 54 is applied after storage of the input activity signals 14 in the RAM 30. The original measured form of the input activity signal 14 is retained in unchanged form in the RAM 30; and therefore, the digital filter 54 can be changed and applied repeatedly to the input activ_¬ ity signal 14 in the process of the user analyzing the signal 14. The digital filter 54 is readily modified by user programming, and consequently the user has great versatility in constructing virtually any combination of low or high pass or band pass filter necessary to analyze the input activity signal 14.

Noise Evaluation The evaluation of a noise signal often enables the user to compensate for the noise by utilizing an electronic filter, such as the digital filter 54, to attenuate the noise signal to provide a reduced, or sub¬ stantially noise-free, form of the input activity signal 14 for more meaningful data analysis. Alternatively, if the user can identify the source of the noise signal, the noise source might be eliminated altogether. Noise iden¬ tification and attenuation or reduction is known in selected areas of biological science (see, for example, Introduction to Automated Arrhythmia Detection, ch.5, K.L. Ripley and A. Murray, IEEE Computer Society, No. EH 0171.9,1980; and see R.H. Wong and R.G. Bickford, "Brain- stem Auditory Evoked Potentials: The Use of Noise Esti¬ mates," Electroencephelography 50, 25-34, (1980); which are incorporated by reference herein).

Another aspect of the analyzer means is noise evaluation alone which is carried out by the apparatus 10 responsive to software programs directed to determination of the noise signals. Knowing the noise signal be- havior, the user can often program the digital filter 54 to attenuate the noise signal. One type of noise evalu¬ ation program is directed to evaluation of noise signals which do not have long terra, constant frequency and amp¬ litude. This type of noise evaluation is directed to, for example, noise signals comprising random noise, spur¬ ious occasional components of irregular frequency and varying amplitude and spurious temporary components of -26-

regular frequency noise.

FIG. 6 illustrates one embodiment of the inven¬ tion used for isolation of extraneous noise signals pres¬ ent in the measurement of brain electrical activity sig- 5 nals. The converted input activity signal 14 output from the A/D converter 28 is input to multiplexer means, such as a multiplexer 56, which distributes and accumulates the activity signal 14 in at least two alternate memory locations, a first memory 57 and a second memory 58. The

10 signal 14 is entered into these locations by alternating data entry between the memory locations 57 and 58. If the noise signal is random noise or is a continuous but irregular frequency signal, the noise signal is charac- terizable by applying subtraction means to generate a

15 subtracted output of the arithmetic difference between the input activity signals 14 in the first memory loca¬ tion 57 and the input activity signals 14 in the second memory location 58. Knowing the noise signal, the user can selectively attenuate this unwanted noise signal

20 using filters, such as the digital filter 54. If, how¬ ever, the noise signal happens to be similar in frequency to the input activity signal 14, the filtration is more difficult. In such cases the user might have to eliminate the source of the noise signal or alter experimental

25 conditions to distinguish and attenuate the noise signal.

The nature of the noise signal to be evaluated also affects the analysis procedure, such as the number of values of the signal 14 to be entered in each of the memory locations 57 or 58 before switching data entry to

30 the other memory location 57 or 58. For evaluating ran¬ dom noise signals, it is acceptable to enter every odd numbered data signal in the first memory location 57 and every even_, numbered data signal in the second memory location 58. For example, when measuring EP response

35 curves, every other set of values which constitute the EP response to the stimulus 16 is accumulated in the first memory location 57 and the other sets of responses are accumulated in the location 58. When the noise spectrum takes other forms, such as a spurious noise burst of irregular frequency and amplitude, correct analysis of the noise signal depends on having a substantial portion of the noise signal iso- lated within one segment (or other identifiable portion) of one of the memory locations 57 or 58. If the noise signal is evenly distributed in the memory locations 56 and 58, this method does not enable one to readily dis¬ tinguish the noise signal portion. Therefore, in gen- eral, data is stored and accumulated in one of a plu¬ rality of memory locations with a user selectable time period for accumulating data in each of the memory loca¬ tions before switching to another of the memory loca¬ tions. For example, ten entries of the signal 14 can be stored in one of a plurality of memory locations before switching to the next memory location for the next ten entries of the signal 14. Accordingly, the user should determine by independent analysis the expected varieties of noise and select the number of data entries and time period for accumulation in each of the memory loca¬ tions. In this manner, noise signals which have a par¬ ticular time duration can be isolated. After determina¬ tion of the noise signal and of the noise corrected form of the input activity signal 14, the user can also evalu- ate the noise signal by calculation of a signal to noise ratio which assists in evaluating the nature and magni¬ tude of the noise signal and provides a way to evaluate the quality of the experimental conditions.

In another form of the invention the apparatus 10 responsive to analyzer means in the form of a software program evaluates the noise signal by performing a Fourier transformation to isolate the frequency compo¬ nents associated with the noise signal. The Fourier transformation is preferably carried out as . a fast Fourier transformation procedure in a conventional manner as indicated hereinafter. Once the noise signal has been evaluated, the digital filter 54 is programmed to atten¬ uate the known noise signal. This Fourier transformation analysis can also be preceded or followed by one of the previously discussed procedures for analyzing the noise signals.

Statistical Analysis Statistical evaluation of an individual patient's characteristic topographical map of brain elec¬ trical activity is accomplished by such conventional approaches as z-statistics and t-statistics (see, for example, U.S. Patent Nos. 4,201,224 (John) and 3,780,724 (John) which are incorporated by reference herein). For example, in the case of z-statistics, the patient re¬ sponse in terms of the input activity signals 14 at each of the points of the topographical map 44 is expressed in terms of the number of standard deviations from the aver- age response of a group of a representative normal popu¬ lation.

Fourier Transformation

The apparatus 10 responsive to a software pro¬ gram carries out a Fourier transformation analysis of the frequency energy components in an EEG measurement. As mentioned hereinbefore, a conventional fast Fourier transformation (FFT) is preferably used to carry out the transformation of the signals 14. The FFT is explained by Oppenheim et al., Digital Signal Processing, ch. 6, Prentice-Hall, Englewood Cliffs, N.J., 1975, which is incorporated by reference herein.

The EEG input activity signals 14 are sampled at predetermined time intervals, approximately 2.5 second segments, to provide a selectable total number of 256 to 2048 segments of the sampled form of the EEG input acti¬ vity signals 14 (see, for example, Ueno et al., "Topo¬ graphic Computer Display of Abnormal EEG Activities in Patients with CNS Diseases," Memoirs of the Faculty of Engineering, Kyushu University, Volume 34, February, 1975, pages 195-209; which is incorporated by reference herein). In the illustrated embodiment sampling means for obtaining the signal samples takes the form of a software program in the disk 29 and is executed by the microcomputer unit 22. The software program actuates measurement of the signals 14 at the predetermined time intervals in accordance with a timing routine. The output from the Fourier transformation analysis of the segments of the input activity signal 14 enables determination of the frequency band energy output present in at least the major EEG frequency bands of α , β , δ and θ. In another form of the invention other subintervals of some of these bands are also evaluated. The frequency band energ outputs can be further analyzed by one of the statistical analysis software programs and/or the noise evaluation programs. The frequency band energy outputs are then processed by the DPU 39, and the video display 43 gener¬ ates the appropriate topographical map 44.

Threshold Activation

In some modes of data acquisition, it is de¬ sirable not to enable, or actuate, accumulation and anal- ysis of data unless the incoming input activity signals 14 attain or exceed a predetermined condition, such as a predetermined threshold amplitude or frequency level. This approach allows particular classes of data to be analyzed without superfluous data being present. For example, epileptic spikes occur intermittently and gen¬ erate a large amplitude spike.

After a preliminary screening of the patient, threshold activation program data in the form of the predetermined condition is established and is placed by the input means (such as the keyboard 23 or the disk 29) into the RAM 30 or into separate hardware means for stor¬ ing and testing the predetermined condition such as threshold test circuitry 55 shown in FIG. 1. The micro¬ computer unit 22 uses the predetermined condition stored in the RAM 30, or embodied within the circuitry 55, to compare with the incoming input activity signals 14. Therefore, the input activity signals 14 are stored and analyzed by the apparatus 10 only if the signal amplitude achieves or exceeds the predetermined condition.

In an alternative form of the invention the apparatus 10, responsive to a software program, carries out a differentiation of the incoming input activity signal 14, and when the amplitude of the differentiated signal exceeds the predetermined condition, the apparatus 10 accumulates and analyzes the signal 14. In this man¬ ner the onset of a sharp spike, such as an epileptic spike having a rapidly changing curve slope, is detected, and the spike subsequently undergoes analysis.

In another form of the invention the apparatus 10, responsive to the threshold activation program data, detects and analyzes a predetermined threshold frequency level by employing frequency means in the form of con¬ ventional frequency counting circuitry (see, for example, "Electronics for Scientists and Engineers", Prentice Hall, Englewood Cliffs, New Jersey, 1967, pages 321-322 and 470-473, which is incorporated by reference here- in). The output from the frequency counting circuit is a signal whose amplitude is proportional to the frequency detected; therefore, the predetermined condition for the threshold- frequency level^" is set to actuate data acquisi¬ tion and analysis of the incoming input activity signal 14 whenever the predetermined frequency level has been exceeded.

In another aspect of the invention the appara¬ tus 10 measures the number of zero crossing events (a form of frequency determination) and data taking is acti- vated upon exceeding a predetermined number of such events. The microcomputer unit 22 or the test circuitry 55 evaluates the algebraic sign for each one of the input activity signals 14 and maintains a running count of the number of changes in the algebraic sign within a given time period. When the number of algebraic sign changes within the given time period exceeds a predetermined number, data accumulation and analysis is activated, and the resulting input activity signals 14 are displayed as the topographical maps 44.

The apparatus 10 responsive to the threshold activation program is able to actuate analysis of any of the input activity signals 14 wherein the user wishes to restrict analysis, for example, to a large amplitude signal, to a high frequency signal or to other selected distinguishable features. Advantages of the threshold activation program include use of less overall storage area in memory for analysis of the signals 14, perform- ance of more detailed data analysis in a given time per¬ iod of actual calculation by the microcomputer and faster and more efficient analysis of a complete data set com¬ pared to the case of analyzing all incoming data.

Integration, Differentiation and Difference Measurements

The apparatus 10 responsive to an integration software program operates on frames of the input activity signals 14 measured for EP responses to characterize the time integrated response output. This integrated output enables an evaluation of spatial locations on the patient's head 13 and/or the time segments of the EP response which make the most important contributions to the input activity signals 14. Integration is carried out over a range of user selected time segments, and in FIG. 7 the integrated output for some of the selectable time segments is displayed in the resulting topographical maps 44. The integrated output of the input activity signals 14 of the topographical maps 44 results in com¬ bining a number of separate smaller time period segments of the input activity signals 14. Therefore, the user views in a small number of the topographical maps 44 the behavior of the input activity signals 14 over a broad time range. The time range of 0 to 240 milliseconds is shown in only six frames of integrated EP response. Such a display mode is therefore beneficial to the user to carry on an evaluation of a large amount of data without requiring separate display of a large number of the topo¬ graphical maps 44 and without having to switch between a large number of the topographical maps 44.

The apparatus 10 responsive to a differentia¬ tion software program operates on frames of the input activity signals 14 from EP responses to characterize the first or second order differential of the EP responses.

This differential response enables an evaluation of loca¬ tions of the time segments which contain the most signif¬ icant contributions to changes (first order) and rate of change (second order) in the amplitude with respect to location and time of the EP response curves. The user can select the spatial location and/or the time interval over which the differentiation is calculated. The analy¬ sis enables spatial and time analysis of rapidly changing EP responses which supplements information obtained from the integration output. The analysis can also be carried out for changes and rate of change in amplitude with respect to location for the EEG input activity signals 14.

The apparatus 10 is also responsive to a dif- ference software program which operates on frames of the input activity signals 14 from the EP responses to evalu¬ ate the arithmetic difference from one of the user selected frames to another, each of the frames character¬ istic of a preselected time after application of the stimulus 16.

Montage Analysis

The apparatus 10 responsive to a computer montage analysis program carries out a difference type of analysis of the input activity signals 14 to isolate and identify features of interest, such as epileptic spikes. The analysis is accomplished by selecting one or more of the electrode sensors 12 as reference electrodes with the rest of the electrode sensors 12 having the role of active electrode sensors 12. The montage analysis is performed by using the input activity signals 14 stored in memory means, such as the RAM 30, and thus repeated actual measurements are unnecessary. In a preferred form of the invention the twenty-one electrode sensors in FIG. 1 are assigned active roles and an additional electrode sensor 12 is attached near the patient's ear to act as the reference electrode sensor 12. The difference form of the input activity signal 14 is calculated, and the values are stored in the RAM 30. The user then views the difference signals 14 and determines the approximate location of the feature of interest. The user next selects new ones of the reference electrode sensors 12 and active electrode sensors 12 which are in close proxi¬ mity to the feature of interest. The difference form of the input activity signals 14 are calculated, and the location and appearance of the feature of interest is isolated with greater precision. This iteration contin- ues by recycling back to the selection of new ones of the reference and active electrode sensors 12 until comple¬ tion of the identification of the feature of interest.

In other forms of the invention for each selected set of the reference and active electrode sen- sors 12, an average value can be calculated for each set of the sensors 12 in every frame of the input activity signals 14. These average values are then subtracted from one another to form the difference form of the sig¬ nals 14. For example, if the feature of interest is a sharp peak extending along a line, the user could select ten of the sensors on one side of the distended peak as reference electrodes and eleven on the other side as active electrodes. The average of each set is then sub¬ tracted from the average of the other for each of the frames. The difference form of the input activity sig¬ nals 14 is then calculated for a selected number of the frames, (for example, the user can select from the 240 frames of the measured EP response taken every four mil¬ liseconds from 0 to 960 milliseconds after the applica- tion of the stimulus 16). As discussed hereinabove, this iterative analysis procedure can be repeated using re¬ cycle means to return to the beginning of the montage iterative analysis procedure by selecting a different set of the electrode sensors 12 as the reference electrode sensor 12. This iterative process is continued until the source of any feature of interest, such as the above mentioned distended type of peak, is identified or iso- lated. This procedure can be programmed to iterate automatically to a solution, or the user can interact to select various combinations of active and reference elec¬ trode sensors 12 to locate the most prominent features. Therefore, the recycle means can be a user signal to return to perform another iterative analysis or can be an interrupt and branching command in the software program to automatically recycle until the specified feature is identified in accordance with predetermined conditions stored in the RAM 30. The resulting set of difference input activity signals are stored in the RAM 30 at loca¬ tions different from the input activity signals 14 and are compared to one another. These difference input activity signals 14 can also undergo the additional anal¬ ysis 40 and provide other forms of the topographical maps 44 of EP response and EEG measurements. Display of the difference signals 14 and their derivatives from the analysis 40 enable diagnosis of disparities associated with brain abnormalities.

Montage analysis has important advantages over the prior art because the instant approach uses only one set of the measured input activity signals 14 which are stored in the RAM 30. Conventional methods, however-, require repeated measurements since the montage analysis proceeds by selecting a first set of one or more refer- ence electrode sensors 12, measuring a set of signals for the remainder of the plurality of the electrode sensors 12, computing and recording the difference of the signals 14, establishing a new set of reference electrode sensors 12 and measuring a new set of differences in the signals 14. This procedure is sequentially repeated until the location of the feature of interest has been isolated. The computer program montage analysis renders unnecessary this time consuming and repetitive task and substantially reduces the time for data taking and analysis.

Cognitive Test Mode

The apparatus 10 responsive to a cognitive testing software program effectuates EP response tests of recognition ability which enables diagnosis of a number of abnormalities (see, for example, U. S. Patent No. 3,901,215 (John) which is incorporated by reference here¬ in). The instant cognitive testing program makes full use of one time period of data acquisition by sorting the responses to a predetermined pattern of mixed or differ¬ ent types of the stimuli 16 into different memory loca¬ tions of the RAM 30. Ordinarily cognitive testing is accomplished by acquiring the input activity signals 14 for a plurality of completely different time periods, wherein each time period is devoted solely to either a regular form of the stimulus 16 and response thereto or to an intermittent form of the stimulus 16 and associated response. Examples of the different types of the stimuli 16 can include a mixture of different amplitude audible tones, tones of different frequency and a tone pattern with intermittent absences of certain anticipated tones.

The microcomputer unit 22 controls administra¬ tion of the predetermined pattern of the stimulus 16 during the cognitive testing mode of operation responsive to the cognitive test software, and therefore the micro¬ computer unit 22 flags each of the applied stimuli 16 and depending on the nature of the stimulus 16 the flagging enables the microcomputer 22 to sort the resulting EP responses comprised of a set of the input activity sig- nals 14 associated with each type of the stimulus 16, into the different respective memory locations. Compari¬ son and analysis, such as statistical analysis, is then performed on the signals 14 stored in the different mem¬ ory locations. This procedure therefore makes data col- lection more efficient and reduces the time to collect sufficient data characteristic of the input activity signals 14. Video Display and Interaction Modes

The apparatus 10 responsive to an interlace software program results in the interpolation and the output to the display memory of the DPU 39 of every other pixel line in one frame to the video display 43. Upon completion of display of every other pixel line in a first complete frame, or first topographical map 44, the program causes return of the raster beam to the beginning of the display cycle to perform alternate pixel line interpolation and display in the next frame, or the next topographical map 44, of the set of pixel lines skipped in the first display cycle. By virtue of having to proc¬ ess and display only every other pixel line of the input activity signals 14, the interlace mode enables an appar- ent increase in display speed by updating at, for exam¬ ple, twelve frames/second the display memory of the DPU 39. The video display 43 therefore generates a plurality of the topographical maps 44 at an apparent rate of near¬ ly twenty-four frames/second because in each frame every other pixel line is displayed. This results in a smooth cartooning effect without apparent loss of resolution to the human eye.

In the interaction modes the mouse 36 or the light pen 34 are preferably used as indicator means. The user generates an input signal so as to interact with the information present on the video display 43 thereby actu¬ ating selected software programs. In the case of the mouse 34, this use takes the form of displaying a variety of selectable routines on the video display 43, moving a cursor to point to a designated label for one of the routines and carrying out the routine by actuating a switch (not shown) on the mouse 36. Similarly, for the light pen 34, the user points to a location on the video display 43, and a screen sensor (not shown) detects the site of the light pen light spot and generates an activa¬ tion output to the microcomputer unit 22 to actuate the appropriate software program. The software program also displays additional information relevant to the displayed topographic map 44, or further calculations can be per¬ formed and displayed. For example, the user is able to selectively display the evoked potential waveforms 50 (illustrated in FIG. 5) for those points on the topo- graphic map 44 designated by the mouse 34 or by the light pen 34.

In another form of the invention, the apparatus 10 responsive to an interaction means in the form of a software program can generate the amplitude of input activity signal contours along any indicated line on the topographical map 44, the line being selected by the cursor of the mouse 36 or by the light pen 34. Further, the software program can act as a map magnifying means by allowing the user to utilize the mouse 36 or the light pen 34 to select an outline of an area of the topograph¬ ical map 44 and expand the delineated portion to fill a selected portion of the video display 43.

While preferred embodiments of the present invention have been illustrated and described, it will be understood that changes and modifications can be made without departing from the invention in the broader as¬ pects. Various features of the invention are set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A distributed system for sensing brain electrical activity of a patient, comprising: a plural¬ ity of remote means, each comprising means for providing brain electrical activity data representative of said patient's brain electrical activity; means for providing a video output responsive to said brain electrical activity data, said video output including an interpo¬ lated form of said brain electrical activity data; and means for providing a topographical map video presenta- tion of said brain electrical activity data responsive to said video output.

2. The apparatus as defined in Claim 1 where¬ in said means for providing a video output comprises a computer responsive to computer software.

3. The apparatus as defined in Claim 2 where¬ in said computer software is input to said computer from a remote source.

4. The system as defined in Claim 1 wherein said video output is interpolated and generated line-by- line and displayed while a next line is being generated.

5. The apparatus as defined in Claim 1 where¬ in at least one of said remote means comprises sensor means disposed on said patient's head for providing said brain electrical activity data, and means for processing said brain electrical activity data to provide brain electrical activity signals.

6. The apparatus as defined in Claim 5 fur¬ ther including analyzer means responsive to said brain electrical activity signals for providing a substantially noise-free form thereof.

7. The system as defined in Claim 1 wherein said brain electrical activity data comprises input ac¬ tivity signals.

8. The system as defined in Claim 5 further comprising means for providing statistically averaged values for said brain electrical activity signals respon- sive thereto.

9. The system as defined in Claim 8 wherein said means for averaging comprises a computer having a random access memory.

10. A distributed system for sensing and dis¬ playing a topographical map of a patient's brain elec¬ trical activity, comprising: remote apparatus for com¬ municating brain electrical activity data responsive to sensed and processed data from a plurality of electrode sensors disposed on a patient's head, wherein said elec¬ trode sensors provide an associated plurality of said brain electrical activity data; computer means for pro¬ viding a video output responsive to said communicated brain electrical activity data; means for displaying said topographical maps of said brain electrical activity responsive to said video output; and color code means for displaying near each of said topographical maps a pre¬ determined set of colors associated with said topograph¬ ical maps, each of said colors representing an associated fixed relative value within a selected closed data set of said brain electrical activity data.

11. The system as in Claim 10 wherein said computer means is responsive to a plurality of said re¬ mote apparatus for providing said video output.

12. The system as in Claim 10 wherein said computer means comprises means for generating a set of interpolated brain electrical activity data for positions between the locations of said plurality of sensors.

13. The system as defined in Claim 10 wherein said computer means comprises a computer responsive to computer software programs for providing said video out¬ put.

14. The system as in Claim 10 further includ¬ ing input means for supplying an input signal responsive to a user input and indicator means connected to be re¬ sponsive to said input signal for actuating selected system functions.

15. The system as defined in Claim 14 further comprising map magnifying means responsive to said input signal for selectively enlarging a predetermined portion of said topographical map display.

16. A system for displaying a topographical map of EEG brain electrical activity in a plurality of frequency bands of a patient, comprising: (a) remote sensor means comprising: (i) a plurality of electrode sensors disposed on a patient's head for measuring EEG input activity signals at each of said plurality of elec- trode sensors; (ii) processing means responsive to said input activity signals for providing an amplified and digitized form of said input activity signals; (b) means for providing a frequency band energy output characteris¬ tic of the energy in each of said plurality of frequency bands responsive to performing a Fourier transform of said amplified and digitized form of EEG input activity signals; and (c) display means for displaying said topo¬ graphical map responsive to said frequency band energy output.

17. The system as in Claim 16 further compris¬ ing: color code means for displaying near each said topographical map a predetermined set of colors associ¬ ated with said topographical map, each of said colors representing an associated fixed relative value within a selected closed set of said topographical maps.

18. The apparatus as defined in Claim 16 fur¬ ther including computer means for generating a set of interpolated EEG input activity signals for positions between the locations of said plurality of sensors, said interpolated EEG input activity signals generated line- by-line.

19. The apparatus as defined in Claim 17 wherein said predetermined set of colors is arrangeable for display alongside a portion of said topographical map.

20. The apparatus as defined in Claim 16 fur¬ ther including a display of at least one EEG curve plot¬ ted near each said topographical map, each said EEG curve characteristic of the amplitude within each said fre¬ quency band.

21. The apparatus as defined in Claim 20 wherein said display of EEG curves are color coded by positioning selected color codes segments along the fre¬ quency axis of said display of the EEG curve, each of said color coded segments associated with a preselected one of said frequency bands.

22. A distributed system for displaying a topographical map of brain electrical activity compris¬ ing: input means for supplying an input signal respon¬ sive to a user input; remote sensor means comprising: (a) a plurality of electrode sensors disposed on a patient's head for providing input activity signals re- sponsive to said brain electrical activity; (b) process¬ ing means responsive to said input activity signals for providing an amplified and digitized form of said input activity signals; storage means for storing and output- ting said amplified and digitized input activity signals; means responsive to said input signal for storing a pre¬ determined condition; threshold means responsive to said amplified and digitized input activity signals for com¬ paring said predetermined condition with said input activity signals and for enabling measurement and selec- tive storage of said amplified and digitized input activity signals in said storage means responsive to measuring attainment of said predetermined condition; computer means for providing a video output responsive to said stored input activity signals; and means for dis- playing said topographical map of said brain electrical activity responsive to said video output.

23. The apparatus as defined in Claim 22 wherein said predetermined condition comprises a prede¬ termined amplitude level and said threshold means com- prises means for sensing an amplitude of said input activity signals and comparing said sensed amplitude with said predetermined amplitude level.

24. The apparatus as defined in Claim 22 wherein said predetermined condition comprises a prede¬ termined differential amplitude level and said threshold means comprises means for determining said differential amplitude of said input activity signals and comparing said differential amplitude with said predetermined dif¬ ferential amplitude level.

25. The apparatus as defined in Claim 22 wherein said predetermined condition comprises a prede¬ termined frequency level and said threshold means com- prises means for determining a frequency of said input activity signals and comparing said frequency with said predetermined frequency level.

26. A distributed system for displaying a topographical map of brain electrical activity remotely sensed by a plurality of electrode sensors disposed on a patient's head, wherein said electrode sensors provide an associated plurality of input activity signals having a noise signal associated therewith, said system compris¬ ing; processing means responsive to said input activity signals for providing an amplified and digitized form of said input activity signals; analyzer means responsive to said amplified and digitized input activity signals for providing a reduced form of said input activity signal, including means for analyzing and attenuating said noise signal accompanying said amplified and digitized input activity signals; computer means for providing a video output responsive to said reduced input activity signals; and means for displaying said topographical maps of said brain electrical activity responsive to said video out- put.

27. The system as defined in Claim 26 wherein said analyzer means comprises: multiplexer means respon¬ sive to said input activity signal for distributing a plurality of said input activity signals; and memory means responsive to said input activity signals for ac¬ cumulating in a plurality of memory locations said input activity signals for selected time periods.

28. A distributed system for displaying a topographical map of brain electrical activity remotely sensed by a plurality of electrode sensors disposed on a patient's head, each of said plurality of electrode sen¬ sors adapted to provide a plurality of input activity 5 signals and each said electrode sensor selectable as an active and a reference electrode sensor, said system further comprising; processing means responsive to said input activity signals for providing an amplified and digitized form of said plurality of input activity sig- ° nals and having a feature of interest included therein; memory means for storing said amplified and digitized form of said input activity signals; montage means re¬ sponsive to said stored input activity signals for iden¬ tifying said feature of interest in said stored signals 5 by carrying out an iterative analysis of said stored input activity signals, said iterative analysis compris¬ ing selection of at least one said active electrode sen¬ sor and at least one said reference electrode sensor from said plurality of electrode sensors, forming a difference 0 input activity signal by subtraction of said stored input activity signal for said active electrode sensor from said stored input activity signal associated with said reference electrode sensor, storing said difference input activity signals in said memory means, and outputting 5 said stored difference input activity signals; computer means for providing a video output responsive to said stored difference input activity signals; means for displaying said topographical maps of brain electrical activity responsive to said video output; and recycle 0 means for returning to said iterative analysis to gen¬ erate a new set of said difference input activity signals corresponding to selection of a new one of said active and said reference electrode sensors and continuing said iterative analysis and displaying said topographical maps 5 until completion of said identification of said feature of interest.

29. An apparatus for displaying a topograph¬ ical map of brain electrical activity of a patient, com- prising: sensor means disposed on a patient's head for providing input activity signals responsive to said brain electrical activity; processing means responsive to said input activity signals for providing an amplified and digitized form of said input activity signals; analyzer means responsive to said amplified and digitized input activity signals for providing a substantially noise-free form of said input activity signals; means for providing a video output responsive to said amplified and digitized input activity signals, said video output including a set of interpolated input activity signals for positions between the locations of said sensor means; and means for displaying said topographical map of brain electrical activity responsive to said video output.

30. The apparatus as defined in Claim 29 wherein said sensor means comprises a plurality of elec¬ trode sensors.

31. The apparatus as defined in Claim 29 fur¬ ther comprising means for providing statistically aver- aged values for said input activity signals responsive to said amplified and digitized input activity signals.

32. The apparatus as defined in Claim 31 wherein said means for averaging comprises a computer having a random access memory.

33. The apparatus as defined in Claim 29 wherein said analyzer means comprises filter means, re¬ sponsive to said amplified and digitized input activity signals, for digitally filtering said input activity signals to provide said substantially noise-free form of said input activity signals.

34. An apparatus for displaying a topographi¬ cal map of brain electrical activity of a patient's head comprising: input means for supplying an input signal responsive to a user input; a plurality of electrode sensors disposed on the patient's head for providing input activity signals responsive to said brain elec¬ trical activity; processing means responsive to said input activity signals for providing an amplified and digitized form of said input activity signals; means responsive to said input signal for storing a predeter¬ mined condition; threshold means responsive to said amplified and digitized input activity signals for com- paring said predetermined condition with said input activity signals and for enabling measurement and storage of said amplified and digitized input activity signals in said means for storing responsive to measuring attainment of said predetermined condition; computer means for pro- viding a video output responsive to said amplified and digitized input activity signals; and means for display¬ ing said topographical map of said brain electrical activity responsive to said video output.

35. An apparatus for displaying a topographi- cal map of brain electrical activity sensed by a plu¬ rality of electrode sensors disposed on a patient's head, wherein said electrode sensors provide an associated plurality of input activity signals having a noise signal associated therewith, said apparatus comprising: proc- essing means responsive to said input activity signals for providing an amplified and digitized form of said input activity signals; analyzer means responsive to said amplified and digitized input activity signals for pro¬ viding a reduced form of said input activity signal, including means for analyzing and attenuating said noise signal accompanying said amplified and digitized input activity signals; computer means for providing a video output responsive to said reduced input activity signals; and means for displaying said topographical maps of said brain electrical activity responsive to said video ^"out¬ put.

36. The apparatus as defined in Claim 35 wherein said analyzer means comprises: multiplexer means responsive to said input activity signal for distributing a plurality of said input activity signals; memory means having a plurality of memory locations responsive to said input activity signals for accumulating in said memory locations said input activity signals for selected time periods; and subtraction means responsive to said input activity signals for selectively subtracting said input activity signals in predetermined ones of said memory locations from said input activity signals in the remain- der _. of said memory locations, said subtraction means characterizing said noise signal accompanying said input activity signals.

37. The apparatus as defined in Claim 36 wherein said memory means comprises two of said memory locations, said noise signal characterized by subtraction from one another of said input activity signals in said two memory locations.

38. An apparatus for displaying a topograph¬ ical map of brain electrical activity sensed by a plural- ity of electrode sensors disposed on a patient's head, wherein said electrode sensors provide an associated plurality of input activity signals, said apparatus com¬ prising: processing means responsive to said input activity signals for providing an amplified and digitized form of said plurality of input activity signals; thres¬ hold means responsive to said amplified and digitized input activity signals for comparing a predetermined condition with said input activity signals and for enabling measurement and storage of said amplified and digitized input activity signals responsive to measuring attainment of said predetermined condition; means for storing said amplified and digitized input activity sig¬ nals responsive to enablement by said threshold means; computer means for providing a video output responsive to said amplified and digitized input activity signals; and means for displaying said topographical maps of said brain electrical activity responsive to said video out¬ put.

39. The apparatus as defined in Claim 38 wherein said predetermined condition comprises a prede¬ termined amplitude level, said threshold means comprising means for sensing an amplitude of said input activity signals and for comparing said amplitude with said prede- termined amplitude level.

40. The apparatus as defined in Claim 38 wherein said predetermined condition comprises a prede¬ termined differential amplitude level, said threshold means comprising means for determining said differential amplitude of said input activity signals and for compar¬ ing said differential amplitude with said predetermined differential amplitude level.

41. The apparatus as defined in Claim 38 wherein said predetermined condition comprises a prede¬ termined frequency level, said threshold means comprising means for determining a frequency of said input activity signals and for comparing said frequency with said prede¬ termined frequency level.

42. An apparatus for displaying a topographi¬ cal map of brain electrical activity having a feature of interest therein and sensed by a plurality of electrode sensors disposed on a patient's head, each of said plu¬ rality of electrode sensors adapted to provide a plu- rality of input activity signals and each said electrode sensor selectable as an active and a reference electrode sensor, said apparatus comprising: processing means responsive to said input activity signals for providing an amplified and digitized form of said plurality of input activity signals; memory means for storing said amplified and digitized form of said input activity sig¬ nals; montage means responsive to said stored input activity signals for carrying out an iterative analysis of said amplified and digitized input activity signals for identification of said feature of interest, said iterative analysis comprising selection of at least one said active electrode sensor and at least one said refer¬ ence electrode sensor from said plurality of electrode sensors, forming a difference input activity signal by subtraction of said stored input activity signal for said active electrode sensor from said stored input activity signal associated with said reference electrode sensor, storing said difference input activity signals and out- putting said stored difference input activity signals; computer means for providing a video output responsive to said stored difference input activity signals; means for displaying said topographical map of brain electrical 5 activity responsive to said video output; and recycle means for returning to said iterative analysis to gen¬ erate a new set of said difference input activity signals corresponding to selection of a new one of said active and said reference electrode sensors and continuing said ° iterative analysis and displaying said topographical maps until completion of said identification of said feature of interest.

43. An apparatus for displaying a topographi¬ cal map of EEG brain electrical activity having a feature 5 of interest in at least one of a plurality of frequency bands characteristic of a patient, comprising: a plural¬ ity of electrode sensors disposed on the head of the patient for measuring EEG input activity signals at each of said plurality of electrode sensors; processing means 0 responsive to said EEG input activity signals for provid¬ ing an amplified and digitized form of said EEG input activity signals; memory means for storing said amplified and digitized form of said EEG input activity signals; montage means responsive to said stored EEG input activity signals for carrying out an iterative analysis of said EEG amplified and digitized input activity sig¬ nals for identification of said feature of interest, said iterative analysis comprising selection of at least one active and at least one reference electrode sensor from among said plurality of electrode sensors, forming an EEG difference input activity signal by subtraction of said EEG input activity signal for said active electrode sen¬ sor from said EEG input activity signal for said reference electrode sensor, storing said EEG difference input activity signals in said memory means and output- ting said stored EEG difference input activity signals; means for sampling said stored EEG difference input activity signals at predetermined intervals to provide a sampled form of said EEG difference input activity sig_¬ nals; means responsive to said stored difference input activity signals for performing a Fourier transformation of said sampled form of said EEG difference input activity signals to provide a frequency band energy out¬ put characteristic of the energy for each of said plu¬ rality of frequency bands; means for displaying said topographical map responsive to said frequency band energy output; and recycle means for returning to said montage means to carry out said iterative analysis by generating a new set of said EEG difference input activity signals corresponding to selection of a new one of said active and said reference electrode sensors and continuing said iterative analysis and displaying said topographic maps until completion of said identification of said feature of interest.

44. A method for sensing brain electrical activity from a plurality of patients comprising the steps of: measuring by a plurality of remote means, brain electrical activity data representative of each of said patient's brain electrical activity; constructing an interpolated form of said brain electrical activity data; generating a video output responsive to said interpolated form of said brairϊ electrical activity data; and generat- ing a topographical map video presentation of said patient's brain electrical activity responsive to said video output.

45. A method for performing in one testing period a cognitive test on a patient having a plurality of electrode sensors disposed on the patient's head, comprising the steps of: applying a predetermined pat¬ tern of mixed stimuli to said patient to generate a set of associated input activity signals responsive to each of said mixed stimuli; sensing said set of associated input activity signals by computer means; sorting by said computer means into different respective memory locations said set of associated input activity signals, each said memory location depending upon the nature of said stimulus associated with said set of input activity sig¬ nals; and analyzing said sorted input activity signals using said computer means.

46. An apparatus for displaying a topographi- cal map of brain electrical activity of a patient, com¬ prising: sensor means disposed on a patient's head for providing input activity signals responsive to said brain electrical activity; processing means responsive to said input activity signals for providing an amplified and digitized form of said input activity signals; means for providing a video output responsive to said amplified and digitized input activity signals, said video output in¬ cluding a set of interpolated input activity signals for positions between the locations of said sensor means, said interpolated input activity signals generated line- by-line and displayed while a next line is being generated; and means for displaying said^" topographical map of said brain electrical activity responsive to said video output.

47. The apparatus as defined in Claim 46 wherein said sensor means comprises a plurality of elec¬ trode sensors.

48. The apparatus as defined in Claim 46 wherein said set of interpolated input activity signals are generated from linear weighted appropriate pairs of said amplified and digitized input activity signals.

49. The apparatus as defined in Claim 46 fur¬ ther comprising means for providing statistically aver¬ aged values for said input activity signals responsive to said amplified and digitized input activity signals.

50. The apparatus as defined in Claim 49 wherein said means for providing averaged values com¬ prises a computer having a random access memory.

51. The apparatus as defined in Claim 46 fur- ther including color code means for displaying alongside said topographical maps a predetermined set of colors displayable on said topographical maps, each of said colors representing an associated fixed relative value within a selected closed data set of said input activity signals.

52. The apparatus as defined in Claim 51 wherein said color code means alongside each said topo- graphical map includes at least said colors being dis¬ played on each said topographical map associated with said color code means.

53. The apparatus as defined in Claim 46 wherein said means for displaying includes a display processing unit having a display memory which can be updated for display of selected ones of said lines of said topographical maps responsive to said input activity signal.

54. The apparatus as defined in Claim 46 wherein said topographic maps are constructed from pixels having a plurality of distinguishable colors, wherein each of said colors is selectively comprised of one unique color and of at least two unique colors mixed in a predetermined manner among near neighbors of said pixels.

55. An apparatus for displaying a topographi¬ cal map of brain electrical activity sensed by a plu¬ rality of electrode sensors disposed on a patient's head, wherein said electrode sensors provide an associated plurality of i-nput activity signals, said apparatus com- prising: processing means for providing an amplified and digitized form of said plurality of input activity sig¬ nals; computer means for providing a video output re¬ sponsive to said plurality of amplified and digitized input activity signals; means for displaying said topo- graphical maps of said brain electrical activity respon¬ sive to said video output; and color code means for dis¬ playing near each of said topographical maps a predeter¬ mined set of colors displayable on an associated one of said topographical maps, each of said colors representing an associated fixed relative value within a selected closed data set of said input activity signals.

56. The apparatus as defined in Claim 55 wherein said computer means includes computer software responsive to said amplified and digitized input activity signals for generating a set of interpolated input acti¬ vity signals for positions between the locations of said plurality of sensors.

57. The apparatus as in Claim 55 further char¬ acterized in that said interpolated input activity sig¬ nals can be generated line-by-line, wherein display of each line is provided while a next line is being gene¬ rated.

58. The apparatus as defined in Claim 55 wherein said predetermined set of colors is positionable along a portion of said topographical map.

59. The apparatus as defined in Claim 55 wherein said predetermined set of colors is positionable on the display along at least one of a vertical scale and a horizontal scale.

60. The apparatus as defined in Claim 55 wherein said video output includes a set of interpolated input activity signals for positions between the loca- tions of said plurality of electrode sensors.

61. The apparatus as defined in Claim 55 fur¬ ther including input means for supplying an input signal responsive to a user input and indicator means connected to be responsive to said input signal for actuating selected software programs.

62. The apparatus as defined in Claim 61 wherein said indicator means can select a line on said topographical map and can actuate said computer means to display amplitudes of said input activity signals along said line.

63. The apparatus as defined in Claim 61 fur¬ ther comprising map magnifying means responsive to said input signal for selectively enlarging a predetermined portion of said topographical map for display.

64. An apparatus for displaying a plurality of topographical maps of brain electrical activity sensed by a plurality of electrode sensors disposed on a patient's head, wherein said sensors provide an associated plural- ity of input activity signals responsive to said brain electrical activity, said apparatus comprising: process¬ ing means connected to be responsive to said input activity signal for providing an amplified and digitized form of said input activity signals; means for providing a video output responsive to said amplified and digitized input activity signals, said video output including a set of interpolated input activity signals for positions between the locations of said plurality of sensors and said interpolated input activity signals can be generated and displayed line-by-line while a next line is being generated by said means for providing a video output; and means for displaying simultaneously a display of a plurality of said topographical maps of said brain elec- trical activity responsive to said video output.

65. The apparatus as defined in Claim 64 wherein said plurality of topographical maps comprises a plurality of different selectable states of said brain electrical activity.

66. The apparatus as defined in Claim 65 wherein said different selectable states comprise an evoked potential response, an integrated time segment of evoked potential response and a Fourier transform of EEG input activity signals.

67. An apparatus for displaying topographical maps of brain electrical activity of a patient's head comprising: a plurality of electrode sensors disposed on said patient's head, said sensors providing an associated plurality of input activity signals in response to said brain electrical activity; processing means connected to be responsive to said input activity signals for provid¬ ing an amplified and digitized form of said input activity signals; means for providing a video output responsive to said plurality of amplified and digitized input activity signals; input means for supplying an input signal responsive to a user input; and means for displaying said topographical maps of said brain elec¬ trical activity responsive to said video output, said display means including display processing means having a display memory which can be updated for display of selected lines of said topographical maps responsive to said input activity signal.

68. The apparatus as defined in Claim 67 wherein said means for providing a video output comprises logic means responsive to computer software programs for providing said video output responsive to said amplified and digitized input activity signals.

69. The apparatus as defined in Claim 67 wherein said video output includes a set of interpolated input activity signals for positions between the loca¬ tions of said plurality of sensors, wherein said interpo¬ lated input activity signals can be generated and dis- played line-by-line while a next line is being generated.

70. The apparatus as defined in Claim.,67 fur¬ ther including color code means for displaying near each of said topographical maps at least a portion of a pre¬ determined set of colors, each of said colors appearing on an associated one of said topographical maps and each of said colors having an associated fixed relative value within a selected closed data set of said input activity signals.

71. The apparatus as defined in Claim 70 wherein said predetermined set of colors is arrangeable for display alongside a portion of said topographical map.

72. The apparatus as defined in Claim 70 wherein said predetermined set of colors is arrangeable for display along at least one of a vertical scale and a horizontal scale.

73. The apparatus as defined in Claim 67 fur¬ ther characterized in that said display includes at least one evoked potential response waveform plotted near each of said topographical maps, each said waveform character¬ istic of an amplitude and time response for a selected location on said topographical map.

74. An apparatus for displaying a topographi- cal map of EEG brain electrical activity in a plurality of frequency bands of a patient, comprising: a plurality of electrode sensors disposed on a patient's head for measuring EEG input activity signals at each of said plurality of electrode sensors; processing means con¬ nected to be responsive to said input activity signals for providing an amplified and digitized form of said input activity signals; means for sampling said EEG input activity signals at predetermined intervals responsive to said input activity signals to provide sampled forms of said EEG input activity signals; means for performing a Fourier transform of said sampled forms of EEG input activity signals responsive thereto to provide a fre¬ quency band energy output characteristic of the energy in each of said plurality of frequency bands; display means for displaying said topographical map .responsive to said frequency band energy output; and color code means for displaying near each said topographical map a predeter¬ mined set of colors displayable on said topographical map, each of said colors representing an associated fixed relative value within a selected closed set of said topo¬ graphical maps.

75. The apparatus as defined in Claim 74 fur¬ ther including computer means responsive to said EEG input activity signals for generating a set of interpola¬ ted EEG input activity signals for positions between the locations of said plurality of sensors, said interpolated EEG input activity signals generated line-by-line and displayed while a next line is being generated by said computer means.

76. The apparatus as defined in Claim 74 wherein said predetermined set of colors is arrangeable for display alongside a portion of said topographical map.

77. The apparatus as defined in Claim 74 fur¬ ther including a display of at least one EEG curve plot¬ ted near each said topographical map, each said EEG curve characteristic of the amplitude within each said fre- quency band .

78. The apparatus as defined in claim 77 wherein said display of EEG curves can be color coded by positioning selected color coded segments along the fre- quency axis of said EEG curve, each of said color coded segments associated with a preselected one of said fre¬ quency bands.