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USE OF LINC-8 FOR EEG DATA REDUCTION

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USE ÓF LINC-8 FOR EEG DATA REDUCTION

Background

Interpretation of EEG Waveforms for information relating to subject state has been an area of long interest to people outside ui the reurophysiological field. A dozen years ago, Norbert Wiener conducted investigations of brain records. He sought to apply to EEG interpretation, some of the statistical communicatioa theory developed by his circle at MIT. This theory has been set forth by Y. W. Lee.' In 1954 Dr. Weiner was particularly interested in "a nominal 10 cps clock pulse" which he hypothesized, formed the basic timing for serial re-ordering of the brain processing organization; he noted state differences associated with this part of the spectrurn in different subjects.

Detailed specific statistical reduction techniques are laid out by Dr. The by Dr.

former attacks reduction in a classical statistical approach, dealing with power spectral estimates. phase functions, zutocovariance and cross covariance functions, transfer functions, ccherency, etc, He uses these descritora to determine significant factors associated with EEG responses. A large number of variablea can be treated simultaneously.

The lattes attacks the problem principally from a "period analysis" standpoint. The basic waveform is clipped and zerocrossover intervals are scrutinized. Similarly, the fizst and second derivatives are processed for clipped periods. The investigator utilizes all three of these on the same time base to examine the spectrum for state evaluation.

The references also give summaries of other recent techniques applied to EEG analysis.

I is intended here to present the results of a modest study caz-ied cut on a\_set of data furnished through the courtesy of Drs. Wor educational purposes. The subject was

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recorded, in three states, on 1/4", 2 track, FM tape run at 7 1/2"/sec as follows:

(at) Drowsy 5 min. (a-2) I kcps tone 5 min. (b-2) 11 (b1) Alpha (cl) Light sleep and Alpha (c-2) 1

Editing and Reduction

The tape was played into the A/D channels of the LINC-a for editing, using the SCOPE-8 program. The three 5 minute samples were examined for gross characteristics, Comments were as iollows:

(a) Drowsy: 30-60 second amplitude (long term) modulation was noted to be present in addition to the 7-10 cps dominant component band.

(b) Alpha: more extreme excursion; less pronounced long term modulation; pronounced short term modulation or beating.

(c) Light Sleep: less pronounced excursions.

. The data was visually edited again and a run made to store the data. This is given in the column'labelled Run I of Table I. It was attempted to recover representative samples of high, intermediate and low signal power. Block storage numnbers are shown.

Next the stored data was examined for spectral content using the program FRQANA; acope camera pictures were taken for comparison in matrix form for significant differences in the various states.

Repeats of data taking was next performed in Runs Ⅱ and Il. Run III was sampled at a lower rate; this gives a longer sample interval.

Next, selected blocks were differentiated once and stored in lccations corresponding to start point l00 ( 000 waveform sample, l00 first derivative, etc.)

0

-2.

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It was feasible to make certain preliminary evaluations of the data at this point. These were:

I. Signal content for discrimination between states was highest for the high points of the long term modulation.

2. A finer frequency resolution was (1/2 cps) more relevant than tho 1 cps resolution. 1

Finaliy a set of runs were made for oscilloscope pictures to show the below format:

1. sampled waveform

2. frequency analysis of (1)

3. first derivative of (1) J。225-

4. frequency analysis of (3)

Results and Conclusions

Figures 1, 2, and 3 show three representative outputs which appeared tentatively as "typical":

1. Drowsy: this is sample 060, 160 of the data, taken at a high point. The waveform is shown at the top: its spectrum is immediately below shown out to 32 cps. A dominant spike shows up at 9 cps; a plateau from 8-13 cps is present, A "characteristic" bump showed up in the.region 14-20 cps.

2. Alpha: this is sample 062, 162; a reduction of the hump at 14-20 cps was noted. A bifurcation or "forking" appeared in the alpha region at the depression at 9 cps. This would explain the beating or short term modulatiou,

3. Light Sleep and Alpha: this is sample 072,172; predominance of the alpha tones is noted with a general shift in energy to the lower end of the spectrum.

For all three samples the first derivative spectrum shows up as expected; namely, the "bluing" of the spectrum by applying a derivative function.

It would appear that a parametric study of BW, frequency. accenting functions (S, S", ete.), examination of phase relation-

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ships, reduction techniques, and other processing would be meaningful, This might permit the design of 1 real time EEG analyzer which would not require a high level of training for operation,

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1. MIT Report A 18I, Y. W. Lee

2.

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ORIGINNC SAHPLE.

SPECTRUN0-22 CPS FIRST DERIW

SPECTRUHOE3ZCPS

DROWSY. STATE E SEC SAMPLE0-32cn.

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IN B 962 2 J

ORIG SAMPLEZ SEC

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FIRST DFRV.

SPECTU032CP.