Eeg system

• US 5,678,559 A
• Filed: 01/23/1995
• Issued: 10/21/1997
• Est. Priority Date: 01/23/1995
• Status: Expired due to Fees

• Current Assignee: Recom Managed Systems, Inc.
• Original Assignee: Budimir S. Drakulic
• Inventors: Drakulic, Budimir S.
• Primary Examiner(s): Jastrzab, Jeffrey R.
• Application Number:
  US08/376,405
• Time in Patent Office: 1,002 Days
• Field of Search: 123/731, 123/734, 123/745, 123/639, 123/644, 123/901, 123/902, 123/908, 123/696, 607/139, 364/413.05
• US Class Current: 600/544
• CPC Class Codes: A61B 5/301 providing electrical separation, e.g. by using isolating transformers or optocouplers
• CPC Class Codes: A61B 5/369 Electroencephalography [EEG] devices for psychotechnics A61B5/16
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal
• CPC Class Codes: Y10S 128/902 Biological signal amplifier

Abstract

Electrodes, preferably paired on a patient'"'"'s head, produce signals representing the patient'"'"'s brain waves at one of the paired electrodes and reference signals at the other paired electrode. Pre-amplifiers juxtaposed to the paired electrodes and having a balanced operation even with impedance differences between the paired electrodes produce signals representing the difference in the signals between such electrodes. After filtering to eliminate DC and band limit the upper frequency, the signals from each pre-amplifier pass to a post-amplifier displaced and electrically isolated from the pre-amplifier. The post-amplifier linearly amplifies the pre-amplifier signals and filters the signals at the lower and upper frequencies within a particular frequency range dependent upon the frequency range in which the investigator is interested. The upper and lower limits of the frequency range are dependent upon the frequencies of controlling clock signals. The upper and lower clock frequencies may be varied progressively to determine the characteristics of the signals produced at the individual ones of the electrodes from brain wave shapes at such electrodes. The cut-off characteristics of the pre-amplifier at the upper and lower frequency limits may be varied by adjusting impedance values in the filter. An electroocular system constructed similarly to, and operative in timed relationship with, the electrode encephalographic system indicates whether signals at the electroencephalographic electrodes result from the patient'"'"'s eye movements. An electrocardiographic system constructed similarly to, and operative in timed relationship with, the electroencephalographic system indicates the relationship between the patient'"'"'s brain and heart waveforms.

Claims

1. In combination for obtaining a person'"'"'s electrocardiogram, comprising:

an electrode constructed to be disposed at a particular position on the head of the person'"'"'s head to produce signals at such electrode in accordance with the brainwaves at such position,

a lead extending from the electrode,

pre-amplifier means disposed in juxtaposition to the electrode and connected to the lead and constructed to provide an output signal amplifying the signal at the electrode and to eliminate noise from such signal,

amplifier means responsive to the output signal from the pre-amplifier means for amplifying such signal,

the electrode constituting a first electrode,

a second electrode constructed to be disposed on the patient'"'"'s head,

a third electrode constructed to be disposed on the patient'"'"'s head and paired with the first electrode, the first electrode providing an information signal and the third electrode providing a reference signal,

the pre-amplifier means including first means responsive to the information signal from the first electrode and the reference signal applied from the third electrode for representing information in the brain waves at the position of the first electrode,

a fourth electrode constructed to be disposed on the patient'"'"'s head and paired with the second electrode, the second electrode providing an information signal and the fourth electrode providing a reference signal,

the pre-amplifier means including second means responsive to the information signal from the second electrode and the reference signal applied from the fourth electrode for passing only the portion of the information signal representing information in the brain waves at the position of the second electrode.

2. In a combination as set forth in claim 1,

the pre-amplifier means including a differential amplifier for passing a signal representing only the difference between the information signal and the reference signal.

3. In a combination as set forth in claim 2,

means responsive in the pre-amplifier means to the signal passing from the differential amplifier for preventing the passage of any DC components in such signal.

4. In combination for obtaining a patient'"'"'s electroencephalogram, comprising:

a plurality of electrodes constructed to be disposed at particular positions on the patient'"'"'s head to produce signals at such electrodes in accordance with the brainwaves at such positions, the electrodes being disposed in pairs with one electrode in each pair providing an information signal and the other electrode in each pair providing a reference signal, the reference electrode in each pair being different from the reference electrode in the other pairs,

first means responsive to the information signal and the reference signal in each of the pairs for providing a balanced operation in passing the portion of the information signal representing the brain wave information for such pair only in a first particular range of frequencies,

second means responsive to the signal passed by the first means for the electrodes in each pair for passing only the portion of the information signal different from the reference signal for such pair, and

third means responsive to the signal from the second means for each pair of electrodes for passing only the portion of such signal above a particular frequency for such pair.

5. In a combination as set forth in claim 4,

the first, second and third means being included in a pre-amplifier and the pre-amplifier being juxtaposed to the electrodes in the plurality.

6. In a combination as set forth in claim 5,

fourth means disposed at a position displaced from the pre-amplifier for amplifying the signal from the third means in the pre-amplifier, and

fifth means for isolating the fourth means from the third means to preserve at the fourth means the characteristics of the signal from the third means.

7. In combination for obtaining an electroencephalogram of a person, comprising:

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head for producing signals representing the brainwaves of the person at such electrodes,

pre-amplifier means constructed to be disposed on the patient'"'"'s head and connected to the electrodes and juxtaposed to the electrodes for producing a pre-amplification of the signals at the electrodes,

means disposed in the pre-amplifier means and responsive to the signals at the electrodes for passing substantially only the signals representing the brain waves of the patient, and

post-amplifier means displaced from the pre-amplifier means and operatively coupled to the pre-amplifier means for amplifying the signals from the pre-amplifier means, the pre-amplifier means including means for passing and pre-amplifying the signals from the electrodes substantially only in a range of frequencies between a pre-selected minimal value and a pre-selected maximal value,

the electrodes being disposed in pairs, one electrode in each pair providing an information signal and the other electrode in each pair providing a reference signal, the reference electrode in each pair being different from the reference electrode in the other pairs,

the pre-amplifier means being operative to pass only the brainwave information in each pair of electrodes.

8. In a combination as set forth in claim 7,

the post-amplifier means having an input,

the post-amplifier means including means for isolating the signals produced by the pre-amplifier means from the input to the post-amplifier means to preserve in the post-amplifier means the characteristics of the signals produced in the pre-amplifier means.

9. In a combination as set forth in claim 7,

the pre-amplifier means including means for establishing a ground for the pre-amplifier means,

the post-amplifier means including means for establishing a ground for the post-amplifier means independent of the ground for the pre-amplifier means.

10. In combination for obtaining an electroencephalogram of a person, comprising:

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head for producing signals representing the brainwaves of the person at such electrodes,

pre-amplifier means connected to the electrodes and juxtaposed to the electrodes for producing a pre-amplification of the signals at the electrodes,

means disposed in the pre-amplifier means and responsive to the signals at the electrodes for passing substantially only the signals representing the brain waves of the patient, and

post-amplifier means displaced from the pre-amplifier means and operatively coupled to the pre-amplifier means for amplifying the signals from the pre-amplifier means,

the post-amplifier means including means for providing signals in individual frequency ranges for the signals from different ones of the electrodes in accordance with the frequency range of the brainwave signals at such different ones of such electrodes.

11. In combination for obtaining an electroencephalogram of a person, comprising;

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head for producing signals representing the brainwaves of the person at the electrodes, the electrodes being paired, a first one of the electrodes in each pair providing signals representing brain wave information and a second one of the electrodes in each pair providing a reference, the reference electrode in each pair being different from the reference electrode in the other pairs,

pre-amplifier means constructed to be disposed on the patient'"'"'s head and operatively coupled to the electrodes in each pair for passing in a particular range of frequencies only the signals representing the brainwaves of the person at the first one of the electrodes in each pair, and

post-amplifier means responsive to the signals passed by the pre-amplifier means in the particular range of frequencies for limiting the individual ranges of frequencies for the signals from the different ones of the first electrodes in the pairs in accordance with the frequency characteristics of the brainwaves of the person at such different ones of the first electrodes in the pairs.

12. In a combination as set forth in claim 11,

the pre-amplifier means including means for passing the signals from the different ones of the first electrodes in the pairs in the particular range of frequencies collectively for such electrodes, the pre-amplifier means being constructed to provide a balanced operation on the signals from the electrodes in each pair, and

the post-amplifier means being responsive to the signals passed by the pre-amplifier means in the particular range of frequencies collectively for the first electrodes in the pairs for passing the signals only in the individual ranges of frequencies within such particular range for the different electrodes in the plurality in accordance with the characteristics of the brainwaves at such different ones of the first electrodes in the pairs.

13. In a combination as set forth in claim 12,

means in the pre-amplifier means for establishing a first ground for the pre-amplifier means, and

means in the post-amplifier means for establishing for the post-amplifier means a second ground independent of the first ground.

14. In a combination as set forth in claim 11,

means in the pre-amplifier means for establishing a first ground for the pre-amplifier means, and

means in the post-amplifier means for establishing for the post-amplifier means a second ground independent of the first ground.

15. In combination for obtaining an encephalogram of a person,

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head for producing signals representing the brain waves of the person at such electrodes,

pre-amplifier means constructed to be disposed on the patient'"'"'s head in juxtaposition to the electrodes and connected to the electrodes for passing in a particular range of frequencies the signals produced at the electrodes in representation of the brainwaves of the person, and

post-amplifier means for amplifying the signals from the pre-amplifier means, and

first means in the post-amplifier means for limiting the range of frequencies in the signals in the post-amplifier means for each individual one of the electrodes in accordance with the frequency characteristics of the brain waves at such individual one of the electrodes to provide an optimal amplification by the post-amplifier means of the signals at such individual one of the electrodes.

16. In combination for obtaining an electroencephalogram of a person, comprising:

A plurality of electrodes constructed to be disposed at particular positions on the persons'"'"'s head for producing signals representing the brain waves of the person at such electrodes,

pre-amplifier means connected to the electrodes for passing in a particular range of frequencies the signals produced at the electrodes in representation of the brainwaves of the person,

post-amplifier means for amplifying the signals from the pre-amplifier means, and

first means in the post-amplifier means for limiting the range of frequencies of the signals in the post-amplifier means for each individual one of the electrodes in accordance with the frequency characteristics of the brain waves at such individual one of the electrodes to provide an optimal amplification by the post-amplifier means of the signals at such individual one of the electrodes,

the electrodes in the plurality being paired to provide signals, at a first one of the electrodes in each pair, representing the brainwaves at such first one of the electrodes and to provide reference signals at a second one of the electrodes in such pair, and

the pre-amplifier means being responsive to the signals produced at the first and second electrodes in each pair to pass only the portion of the signals at the first one of electrodes in such pair different from the signals at the second one of the electrodes in such pair.

17. In a combination as set forth in claim 16,

second means in the post-amplifier means for isolating the post-amplifier means from the pre-amplifier means,

the first means in the post-amplifier means limiting the signals from the first one of the electrodes in each of the different pairs to an individual range of frequencies in accordance with the range of frequencies in the brainwaves of the person at such first one of the electrodes,

the pre-amplifier means constructed to be disposed on the person'"'"'s head in juxtaposition to the electrodes.

18. In a combination as set forth in claim 17,

the second means constituting optical means for isolating the post-amplifier means from the pre-amplifier means.

19. In combination for obtaining an electroencephalogram of a person, comprising:

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head for producing signals representing the brain waves of the person at such electrodes,

pre-amplifier means constructed to be disposed on the person'"'"'s head and connected to the electrodes for passing in a particular range of frequencies the signals produced at the electrodes in representation of the brainwaves of the person,

post-amplifier means for amplifying the signals from the pre-amplifier means, and

first means in the post-amplifier means for limiting the frequency range of the signals in the post-amplifier means for each individual one of the electrodes in accordance with the frequency characteristics of the brainwaves at such individual one of the electrodes to provide an optimal amplification by the post-amplifier means of the signals at such individual one of the electrodes, and

second means in the post-amplifier means for isolating the post-amplifier means from the pre-amplifier means.

20. In combination for obtaining an electroencephalogram of a person, comprising:

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head for producing signals representing the brain waves of the person at such electrodes,

pre-amplifier means connected to the electrodes for passing in a particular frequency range the signals produced at the electrodes in representation of the brain waves of the person,

post-amplifier means for amplifying the signals from the pre-amplifier means, and

first means in the post-amplifier means for establishing frequency characteristics in the post-amplifier means for each individual one of the electrodes in accordance with the frequency characteristics of the brain waves at such individual one of the electrodes to provide an optimal amplification by the post-amplifier means of the signals at such individual one of the electrodes,

the first means in the post-amplifier means providing an individual range of frequencies for the signals from each of the different electrodes only in accordance with the individual range of frequencies at such electrodes in the brainwaves of such person.

21. In combination for obtaining a person'"'"'s electroencephalogram, comprising;

a plurality of electrodes constructed to be disposed at particular positions on the persons'"'"'s head to produce signals at such electrodes in accordance with the brainwaves of such person at such positions,

means for amplifying the signals at the electrodes,

low pass filter means operatively coupled to the amplifying means to pass the signals from the amplifying means,

the signals at each of the electrodes having an individual range of frequencies in accordance with the positioning of such electrode on the patient'"'"'s head, and

means for varying the range of frequency response of the low pass filter means at progressive instants of time to determine the characteristics of the signals at such individual ones of the electrodes in accordance with the frequency range of the waveforms at such individual one of the electrodes.

22. In a combination as set forth in claim 21,

the low pass filter means having, at the upper end of the range of frequency response, a cut off where the amplitude response to the signals passing through the low pass filter means decreases with progressive increases in frequency, and

means for varying the cut off response of the low pass filter means.

23. In a combination as set forth in claim 21,

the amplifying means including pre-amplifier means disposed in juxtaposed relationship to the electrodes for providing a pre-amplification of the signals from the electrodes and including post-amplifier means displaced from the electrodes and the pre-amplifier means and responsive to the signals from the pre-amplifying means for amplifying such signals.

24. In a combination as set forth in claim 23,

the electrodes in the plurality being connected in pairs to the pre-amplifying means, a first one of the electrodes in each pair providing the signal indicating the brain waveform at the position of such electrode and the other electrode in each pair providing a reference signal,

the pre-amplifying means being responsive to the signals from the electrodes in each pair to pre-amplify the portion of the signal from the first one of the electrodes in each pair that is different from the reference signal produced by the other one of the electrodes in such pair.

25. In a combination as set forth in claim 23,

means in the amplifier means for isolating the pre-amplifier means from the post-amplifier means while preserving the characteristics in the post-amplifier means of the signals from the pre-amplifier means.

26. In a combination as set forth in claim 23,

the pre-amplifier means having a ground,

means in the post-amplifier means for passing through the post-amplifier means the characteristics of the signals in the pre-amplifier means and for providing a ground in the post-amplifier means independent of the ground in the pre-amplifier means,

the low pass filter means having, at the upper end of the range of frequency response, a cut off where the amplitude response to the signals passing through the low pass filter means decreases with progressive increases in frequency, and

means for varying the cut off response of the low pass filter means,

the electrodes being connected in pairs to the pre-amplifying means, a first one of the electrodes in each pair providing the signal indicating %he brain waveform at the position of such electrode and the other electrode in such pair providing a reference signal, the reference electrode in each pair being different from the reference electrode in the other pairs,

the pre-amplifying means being responsive to the signals from the electrodes in each pair to pre-amplify the portion of the signal from the first one of the electrodes in each pair that is different from the reference signal from the other one of the electrodes in such pair.

27. In combination for obtaining a person'"'"'s electroencephalogram, comprising:

first electrodes constructed to be disposed on the person'"'"'s head for producing first signals indicating the person'"'"'s brainwaves at the positions of the electrodes and having first impedances,

second electrodes constructed to be disposed on the patient'"'"'s head for producing reference signals and having second impedances different from the first impedances,

each of the first electrodes being paired with an individual one of the second electrodes,

first means operative in a balanced mode even with the differences in impedances at the first and second electrodes in each pair for providing a pre-amplification of only the portions of the signal from the first electrode in such pair different from the reference signal at the second electrode in such pair, and

second means for amplifying the signal from the first means for each pair of electrodes in an electrically isolated relationship to the first means for such pair of electrodes.

28. In a combination as set forth in claim 27,

the signal on each of the first electrodes having a particular range of frequencies dependent upon the positioning of such first electrode on the person'"'"'s head, and

third means for amplifying the signal from the second means for each of the first electrodes only in the particular range of frequencies for the signal on such first electrode.

29. In a combination as set forth in claim 27,

the first means being disposed in juxtaposed relationship to the first electrode.

30. In a combination as set forth in claim 27,

a third electrode constructed to be disposed on the patient'"'"'s head for producing a third signal indicating the brainwaves of the person at the position of the electrode and having a third impedance,

the reference signal constituting a first reference signal,

a fourth electrode constructed to be disposed on the patient'"'"'s head for producing a second reference signal having a fourth impedance different from the third impedance,

third means operative in a balanced mode even with the difference in impedance at the third and fourth electrodes for providing a pre-amplification of only the portion of the signal from the third electrode different from the second reference signal, and

fourth means for amplifying the signal from the third means in an electrically isolated relationship to the third means.

31. In combination for obtaining a person'"'"'s electroencephalogram, comprising:

a plurality of electrodes constructed to be disposed in spaced relationship to one another on the person'"'"'s head, the electrodes being paired to define in each pair a first electrode providing an information signal indicating the brainwave of the person at the position of the first electrode and a second electrode providing a reference signal, the second electrode in each pair being different from the second electrode in the other pairs,

a plurality of pre-amplifier means each responsive to the signals from the first and second electrodes in an individual one of the pairs to produce a pre-amplified signal representing the portion of the information signal at the first electrode in the associated pair different from the reference signal at the second electrode in the associated pair, and

a plurality of amplifier means each responsive to the signal from an individual one of the pre-amplifier means for amplifying the pre-amplified signal from the individual one of the pre-amplifier means only in an individual range of frequencies dependent upon the position of the first electrode providing in the associated pair the signal of the person'"'"'s brainwave to the individual one of the pre-amplifier means.

32. In a combination as set forth in claim 31 wherein

the plurality of pre-amplifier means are disposed on the person'"'"'s head in juxtaposed relationship to the electrodes in the plurality.

33. In a combination as set forth in claim 32, comprising:

means responsive in each of the amplifier means to the signal from the associated one of the pre-amplifier means, but in electrically isolated relationship to such pre-amplifier means, to provide a substantially linear amplification of the signal from such pre-amplifier means.

34. In combination for obtaining a person'"'"'s electroencephalogram, comprising:

a plurality of electrodes constructed to be disposed in spaced relationship to one another on the person'"'"'s head, the electrodes being paired to define in each pair a first electrode providing an information signal indicating the brainwave of the person at the position of the first electrode and a second electrode providing a reference signal,

a plurality of pre-amplifier means each responsive to the signals from the first and second electrodes in an individual one of the pairs to produce a pre-amplified signal representing the portion of the information signal at the first electrode in the associated pair different from the reference signal at the second electrode in the associated pair,

a plurality of amplifier means each responsive to the signal from an individual one of the pre-amplifier means for amplifying the pre-amplified signal from the individual one of the pre-amplifier means in an individual range of frequencies dependent upon the position of the first electrode providing in the associated pair the signal of the person'"'"'s brainwave to the individual one of the pre-amplifier means, and

means for providing progressive changes in the frequency range of the signals amplified by the amplifier means in the plurality to obtain an amplification in the signal from each individual one of the amplifier means upon the production of the range of frequencies individual to the signal in such amplifier means.

35. In combination for obtaining a person'"'"'s electroencephalogram, comprising:

an electrode constructed to be disposed at a particular position on the person'"'"'s head to produce signals at such electrode in accordance with the brainwaves at such position,

a lead extending from the electrode,

pre-amplifier means disposed in juxtaposition to the electrode and connected to the lead and constructed to provide an output signal amplifying the signal at the electrode and to eliminate noise from such signal,

amplifier means responsive to the output signal from the pre-amplifier means for amplifying such signal,

the electrode constituting a first electrode and being constructed to be disposed at a first particular position on the person'"'"'s head,

a second electrode constructed to be disposed at a second particular position on the person'"'"'s head near the person'"'"'s eye to produce electroocular signals at such second electrode in accordance with the brainwaves of the person at such position,

the amplifier means constituting first amplifier means, and

second amplifier means responsive to the signal from the second electrode for amplifying such signal, and

means for simultaneously recording the signals from the first and second amplifier means.

36. In a combination as set forth in claim 35,

a third electrode paired with the first electrode to provide a first reference signal,

a fourth electrode paired with the second electrode to provide a second reference signal,

the pre-amplifier means being responsive to the signals on the first and third electrodes to amplify the differences between the signals from the first and third electrodes, and

the second amplifier means being responsive to the signals from the second and fourth electrodes to amplify the differences between the signals from the second and fourth electrodes.

37. In combination for obtaining a patient'"'"'s electroencephalogram, comprising:

a plurality of electrodes constructed to be disposed at particular positions on the patient'"'"'s head to produce signals at such electrodes in accordance with the brainwaves at such positions, the electrodes being disposed in pairs with one electrode in each pair providing an information signal and the other electrode in each pair providing a reference signal,

first means responsive to the information signal and the reference signal in a particular one of the pairs for providing a balanced operation in passing the information signal only in a first particular range of frequencies,

second means responsive to the signal passed by the first means for passing only the portion of the information signal different from the reference signal,

third means responsive to the signal from the second means for passing only the portion of such signal above a particular frequency,

the reference signal constituting a first reference signal,

at least a second pair of electrodes constructed to be disposed on the person'"'"'s head near the person'"'"'s eyes to produce electrooculogram signals indicating movements of the person'"'"'s eyes and to produce a second reference signal different from the first reference signal, and

fourth means responsive to the signals from the second pair of electrodes for producing the portion of the electroencephalogram signals different from the second reference signal.

38. In a combination as set forth in claim 37,

means for simultaneously recording the signals from the third means and the fourth means for purposes of comparison of such signals to eliminate the effects of eye movements from the signals from the third means.

39. In a combination as set forth in claim 38,

the pre-amplifier means including means for passing and pre-amplifying the signals from the electrodes substantially only in a range of frequencies between a pre-selected minimal value and a pre-selected maximal value, and

the post-amplifier means having an input,

the post-amplifier means including means for isolating the signals produced by the pre-amplifier means from the input to the post-amplifier means to preserve in the post-amplifier means the characteristics of the signals produced in the pre-amplifier means,

the pre-amplifier means including means for establishing a ground for the pre-amplifier means,

the post-amplifier means including means for establishing a ground for the post-amplifier means independent of the ground for the pre-amplifier means.

40. In combination for obtaining an electroencephalogram of a person, comprising;

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head for producing signals representing the brainwaves of the person at the electrodes,

pre-amplifier means operatively coupled to the electrodes for passing in a particular range of frequencies only the signals representing the brainwaves of the person at different ones of the electrodes in the plurality, and

post-amplifier means responsive to the signals passed by the pre-amplifier means in the particular range of frequencies for passing the signals in individual ranges of frequencies for the different ones of the electrodes in the plurality in accordance with the characteristics of the brainwaves of the person at such different ones of the electrodes,

an additional electrode constructed to be disposed at a particular position on the person'"'"'s head near the person'"'"'s eye for producing signals representing the electrooculogram of the person, and

amplifier means responsive to the signals from the additional electrode for producing amplifications of such signals.

41. In a combination as set forth in claim 40,

means for simultaneously recording the signals from the post-amplifier means and the amplifier means.

42. In a combination as set forth in claim 40,

means in the pre-amplifier means for establishing a first ground for the pre-amplifier means,

means in the post-amplifier means for establishing for the post-amplifier means a second ground independent of the first ground, and

means in the amplifier means for establishing for the amplifier means a third ground independent of the first and second grounds.

43. In a combination as set forth in claim 41,

means in the pre-amplifier means for establishing a first ground for the pre-amplifier means,

means in the post-amplifier means for establishing for the post-amplifier means a second ground independent of the first ground, and

means in the amplifier means for establishing for the amplifier means a third ground independent of the first and second grounds,

the pre-amplifier means including means for passing the signals from the different ones of the electrodes in the particular range of frequencies collectively for such electrodes, and

the post-amplifier means being responsive to the signals passed by the pre-amplifier means in the particular range of frequencies for passing the signals in the individual ranges of frequencies within such particular range for the different electrodes in accordance with the characteristics of the brainwaves at such different ones of the electrodes.

44. In combination for obtaining an electroencephalogram of a person, comprising:

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head for producing signals representing the brain waves of the person at such electrodes,

pre-amplifier means connected to the electrodes for passing the signals produced at the electrodes in representation of the brain waves of the person,

post-amplifier means for amplifying the signals from the pre-amplifier means,

first means in the post-amplifier means for establishing characteristics in the post-amplifier means for each individual one of the electrodes in accordance with the characteristics of the brain waves at such individual one of the electrodes to provide an optimal amplification by the post-amplifier means of the signals at such individual one of the electrodes,

an additional electrode constructed to be disposed at a particular position on the person'"'"'s head near the person'"'"'s eye for producing signals representing the electrooculogram of the person, and

amplifier means responsive to the signals from the additional electrode for producing amplifications of such signals.

45. In a combination as set forth in claim 44,

means for simultaneously recording the signals from the post-amplifier and the amplifier means.

46. In combination for obtaining an electroencephalogram of a person, comprising:

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head for producing signals representing the brain waves of the person at such electrodes,

pre-amplifier means connected to the electrodes for passing the signals produced at the electrodes in representation of the brainwaves of the person,

post-amplifier means for amplifying the signals from the pre-amplifier means,

first means in the post-amplifier means for establishing characteristics in the post-amplifier means for each individual one of the electrodes in accordance with the characteristics of the brain waves at such individual one of the electrodes to provide an optimal amplification by the post-amplifier means of the signals at such individual one of the electrodes,

second means in the post-amplifier means for isolating the post-amplifier means from the pre-amplifier means,

an additional electrode constructed to be disposed at a particular position on the person'"'"'s head near the person'"'"'s eye for producing signals representing the electrooculogram of the person, and

amplifier means responsive to the signals from the additional electrode for producing an amplification of such signals.

47. In a combination as set forth in claims 46,

means for simultaneously recording the signals from the post-amplifier means and the amplifier means,

the second means constituting optical means.

48. In combination for obtaining a person'"'"'s electroencephalogram, comprising;

a plurality of electrodes constructed to be disposed at particular positions on the persons'"'"'s head to produce signals at such electrodes in accordance with the brainwaves of such person at such positions,

means for amplifying the signals at the electrodes,

low pass filter means operatively coupled to the amplifying means to pass the signals from the amplifying means,

the signals at each of the electrodes having an individual range of frequencies in accordance with the positioning of such electrode on the patient'"'"'s head,

means for varying the range of frequency response of the low pass filter means at progressive instants of time to determine the characteristics of the signals at such individual ones of the electrodes in accordance with the frequency range of the waveforms at such individual one of the electrodes,

an additional electrode constructed to be disposed at a particular position on the person'"'"'s head to produce at such additional electrode signals representing electrooculograms of the movements of the person'"'"'s eyes, and

means for amplifying the signals at the additional electrode,

the varying means being operative to vary the response of the additional amplifying means at the progressive instants of time to determine the characteristics of the signals at such individual electrode.

49. In a combination as set forth in claim 48,

means for simultaneously recording at each progressive instant of time the signals produced by the amplifying means for the signals at the electrodes and the amplifying means for the signals at the additional electrodes.

50. In a combination as set forth in claim 48,

the electrodes in the plurality being connected in pairs to the pre-amplifying means, a first one of the electrodes in each pair providing the signal indicating the brain waveform at the position of such electrode and the other electrode in each pair providing a reference signal,

the pre-amplifying means being responsive to the signals from the electrodes in each pair to pre-amplify the portion of the signal from the first one of the electrodes in each pair that is different from the reference signal at the other electrode in such pair.

51. In a combination as set forth in claim 49,

a plurality of electrodes constructed to be disposed at particular positions on the person'"'"'s head to produce signals at such electrodes in accordance with the brainwaves of such person at such positions,

means for amplifying the signals at the electrodes,

low pass filter means operatively coupled to the amplifying means to pass the signals from the amplifying means,

the signals at each of the electrodes having an individual range of frequencies in accordance with the positioning of such electrode on the patient'"'"'s head,

means for varying the range of frequency response of the low pass filter means at progressive instants of time to determine the characteristics of the signals at each individual ones of the electrodes in accordance with the frequency range of the waveforms at such individual one of the electrodes,

the additional electrode being paired with a further electrode whereby the further electrode provides a reference signal.

52. In combination for obtaining a person'"'"'s electroencephalogram, comprising:

a first electrode constructed to be disposed on the person'"'"'s head for producing a first signal indicating the person'"'"'s brainwaves at the position of the electrode and having a first impedance,

a second electrode constructed to be disposed on the patient'"'"'s head for producing a reference signal having a second impedance different from the first impedance,

first means operative in a balanced mode even with the differences in impedance at the first and second electrodes for providing a pre-amplification of only the portions of the signal from the first electrode different from the reference signal,

second means for amplifying the signal from the first means in an electrically isolated relationship to the first means,

the signal on the first electrode having a particular range of frequencies dependent upon the positioning of the first electrode on the person'"'"'s head,

third means for amplifying the signal from the second means in the particular range of frequencies,

the particular range of frequencies constituting a first particular range,

a second electrode constructed to be disposed on the person'"'"'s head for producing a second signal indicating the movements of the person'"'"'s eyes,

the signal on the second electrode having a second particular range of frequencies dependent upon the positioning of the second electrode, and

fourth means for amplifying the signal from the second electrode in the second particular range of frequencies.