Cortical activation during steady and changing visual stimulation

371

EUECTROENCEPItALOGRAPHYAND CLINICAL NEUROPHYSIOLOGY

CORTICAL

ACTIVATION

CHANGING

DURING

VISUAL

STEADY AND

STIMULATION

THOMAS MULHOLLAND AND SYLVIA RUNNALS Perception Laboratory, V. A. Hospital, Bedford, Mass. ( U.S.A ) (Accepted for publication: December 7, 1963)

The orienting reflex is identified by non-specificity with regard to the quality and intensity of the stimulus and selectivity of habituation to various stimulus characteristics with repeated presentation (Sokolov 1963). in this experiment, series of cortical activation responses occurring in response to alternating increments and decrements of illumination were evaluated to test the hypothesis that cortical activation had the same duration and latency regardless of the direction of change of illumination. Series of cortical activation responses were produced with a stimulus-brain response feedback loop (Mulholland and Runnals 1962). A positive feedback loop tends to hold at a maximum or minimum or swing erratically between these two extremes. A negative loop tends to stabilize at some level and exhibit only small variations around it. This difference between positive and negative feedback provides a means for testing the hypothesis that increments and decrements of visual stimulation have opposite effects on cortical activation and deactivation. If increments of illumination caused cortical activation and decrements deactivation, when the occurrence of alpha was associated with decrease of stimulation and the occurrence of activation with an increase, then the loop would hold at a limit of continuing activation or the opposite limit of continuing alpha or erratically swing between these limits. However, if cortical response to increment and decrement of stimulation were an identical nonspecific activation, then the loop configuration described before would behave the same as the reverse configuration, i.e., where alpha was associated with an increase and activation a decrease of stimulation. The response of the loop to

a change of stimulation would be the same regardless of the direction of change. METHOD

Material Fifty-three normal men and women were tested. None of these subjects reported using tranquilizers or sedating medication. All subjects were volunteers and employees of the hospital. Apparatus A stimulus-brain response feedback loop was used (Mulholland and Runnals 1962). Visual stimulation was provided by two 100 W lamps located in the medten plane 8 ft from the subject. During feedback one light was on continuously while the other was on intermittently. The steady light was set at three different levels using a volt. age regulator. The intermittent light had a fixed value. By suitably combining the steady and intermittent light both increments and decrements of illumination could be produced, in Table I the illumination values in foot candles for each combination (A, B and C, see below) of intermittent and steady light ate presented. Since the subject's eyes were always closed, the stimulating light was diffuse, of lower intensity and different color compared to the measured light. When the light was on it did not flicker. TABLE ! Illuminationvaluesin foot candles Condition-group Continuous Continuousplus light alone intermittentlight A

0.10

B

! .6

C

5.0

9.2 10.0 14.1

Electroenceph. clin. Ncurophysiol., 1964, 17:371-375

372

T. MULHOLLANDAND S. RUNNALS

Procedure Subjects were assigned to two groups. One group (N =, 30) during.feedback received an increment of stimulation ~hen alpha occurred and the reverse decrement when cortical activation occurred. This was the "increment" or i-group. The other group ( N = 23) duringfeedback received a decrement of illumination when alpha occurred and the reverse increment when cortical activation occurred. This was the "decrement" or D-group. Within each group, subjects were further divided into grcups A, B and C which received the illumination values shown in Table I. For example, I-group (A) during feedback received an increment from 0.1 to 9.2 ft c. when alpha occurred, and received the reverse decrement when activation occurred. D-group (B) received a decrement from !0.0 t~ 1.6 ft c. when alpha occurred and the reverse increment when activation occurred, etc. The numbers of subjects in each subgroup were: i-group: (A) = 9; (B) = I I ; (C) = 10; Dgroup: (A) ~ 8; (B) = 8; (C) = 7. The sequence of stimulation series was the same for each subject. First, a resting record was obtained. This was followed by the steady visual stimulus, which began with a loud click, it was expected that by providing a situation where activation could begin at a high level and decline under homogeneous conditions, minimum differences between I- and D-groups would occur which would be a baseline against which to con~. pare the results of subsequent conditions. After about 30 alpha and no-alpha events had occurred, feedback stimulation was started using the inter. mittent light (no click) superimposed on the continuing steady light. For the l-group the light was turned ON when alpha occurred and OFF when no-alpha occurred. For the D-group it was turned OFF when alpha occurred and ON when no-alpha occurred. The lower limit of the illumination change was the value of the steady light. After at least 30 alpha and no-alpha events had occurred, feedback ceased and the continuous stimulus alone was presented (no click). After 30 alpha and no-alpha events had occurred, all visual stimulation was removed (loud click) and ten successive alpha and no-alpha events were recorded. Durations of alpha and no-alpha events were

indexed by the durations of ON1 and ON2 responses of the relay which was driven by the occurrence or non-occurrence of alpha. The threshold of relay response in terms of alpha amplitude was adjusted to produce the best following of alpha by the relay for each individual subject. During feedback stimulation the relay ONx produccd a stimulus pulse (positive or negative depending on the loop configuration) having the same duration as the relay ON1; relay ONe produced the reverse stimulus pulse having the same duration as the relay ONe. Measurements were to the nearest O. I sec. The time between onset of alpha and relay ON was about 0.2 sec; the time between onset of no-alpha (activation) and relay OFF was between 0.3 and 0.4 sec. RESULTS

General differences between resting, steady and feedback stimulation FiB. I presents the mean durations of ON1 (alpha) and ONe (no-alpha) events for the various stimulation series and l. and D-groups. Condition-groups A, B, and C were pooled t. For both groups, the onset of steady illumination (with a Io,d ¢!i¢k) caused a decrease of ON1 (alpha) durations and an increase of ONe (no-alpha) durations followed by a decrease of ON2 durations and an increase of ONt durations. A hyperbola was fitted to the ON2 durations; a straight line to the ON1 durations, With the onset of feedback stimulation ONe (no-alpha) durations increased and ONt (alpha) durations decreased. A hyperbolic function approximated the decline of ONe durations during feedback. These functions had constants different from those of the curves fitted to the initial steady illumination results. With the onset of steady stimulation again ONe (no-alpha) durations increased slightly, while ONl (alpha) durations also increased, A hyperbola approximated the successive ONl durations; a straight line, the successive ON1 durax The continuous curves (durations, Y, in sec as a function of serial position, X) were fitted by ttial and error to the average of the !- and D-group results, which provided an approximation to the results at the discrete serial positions. The curves drawn with dashed lines provide a range of :EO,5 sec from the fitted solid curve, The equations for the fitted curves arc included in Fig. 1.

Electroencepk. clin. Neurophysiol., 1964, 17:371-375

373

BEG AND VISUAL STIMULATION

.

REST. CLICK - STEADY STIMULUS ' o--o Z-GROUP

FEEDBACK

CLICKRESTING

STEADY STIMULUS

STIMULUS

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1.8

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I l

I

I I

lad 3 -

0

I I

I

II

I

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I I

I

I

l

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I

l

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I

I

i

i

i

. Y. ,025X ÷ 1.2

Y- .02X + 1.0

. . . .

i

i

i"~iii

ON2

Y=.OO?X ÷ 0.7

I

'

" 1 0 4 -2 2 6 1014 182226

SERIAL

l l l l l l l l l l l l l l

v=.ozx,o.e 0 NI I

|II|

i i i i 1 1 1 1 1 1

i

2 6 I0 14 16222830 2 6 I0 14 1 8 2 2 2 6 3 0 2

POSITION OF EVENT

s I

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6 I0

Fig. I Mean durations of ONj (alpha) and ON= (no-alpha) events for each serial position. D-group is designated by filled circles; 1-group by open circles. The equations are for the fitted curve. The dashed curves provide a range of-t-0.3 sec around the solid average curve,

tions. These functions had different constants than the ones previously described. With the onset of the final "resting" period (with a loud click) a typical, rapidly declining activation was seen.

Differences between i- and D-groups For the condition of feedback stimulation, average ON1 and ONe durations from each sub. jeer were analyzed using analysis of variance. There were no significant differences between land D-groups, nor between levels of illumination. As can be seen in Fig. I there were no overall differences between I- and D-groups. During feedback both groups gave similar results. In Table II, the average durations pooled over 30 events and condition,~ A, B and C are present° ed for I- and D-groups separately. Each D-group mean is based on 2,070 events for stimulating

conditions and 690 events for each resting condition; each l-group mean is based on 2,700 for each stimulating condition and 900 for each resting condition. For these data, ON1 and ONe durations were slightly longer for the D-group compared to the l-group. However, none of these differences was statistically significant. When correction is made for the relay ON and OFF lags relative to alpha occurrence by adding 0.2 sec to ONe durations and subtracting 0.4 sec from ONt durations, the average latency during feedback is 0.4 sec and the average duration is 2.6 sec. Variation between and within individuals was large. The distribution of ON and OFF durations was not normal but resembled a Poisson distribution. These individual variations were lost by averaging and are not represented in the data presented previously. The hyperbolic and linear

TABLE 11 Average durations (sec) of ON1 (alpha) and ON= (no-alpha) events Stimulus series Resting Dick-steady *_ti.m..~,,.~ Feedback stimulus Steady stimulus Cliek-"resting"

D-Group 1.2 I. I 0.9 1.8 !.0

ON1 l-Group 1.4 1.3 0.7 !.5 1.3

Xost , 1.3 1.2 0.8 1.6 1.2

D-Group I.~ 1.6 2.5 1.8 2.2

ONa I-Group

XoN~

1.4 2.0 2.2 2. I 3.1

1.5 1.8 2.4 2.0 2.6

Electroenceph. clin. Neurophysiot., 1964, 17:371-375

T. MULI4OLLAND A N D S. RUNNALS

374

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t

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r"-"l_....f-"~

m,

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i'--'t

l'q

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r'----L_

Fig. 2 Parietal-(xcipital records from six different normal subjects. See text for explanation. Sixty cycle filters were used. Curved line intersecting A shows curvilinearity of pen excursion. Amplitude calibrations are not provided since they were not related in a consistent way with system performance. The threshold for stimulus occurrence in terms of alpha amplitude was adjusted to produce the best following of alpha by the stimulus relay yet keeping response to transients and other frequencies to a minimum. Thus the systeat~iain was not necessarily the same for each subject.

functions presented in Fig. 1 must be considered as empirical fits which are not necessarily repre. sentative of any ¢i;;glcindividual. In Fig. 2, EEGs from six subjects ate preset~ted. On the event marker below each record, the upper level is an increment, the lower, a decre. ment of illumination. In records A and B, alpha produces a decrease (14.1 to 5.0 ft c.) and no-alpha an increase (5.0 to 14.1 ft c.) of illumination. Records C and D were obtained during steady illumination at 1.6 ft c. (C), and 0.10 ft c. (D). In record E, alpha is associated with an increase (0.1 to 9.2 ft c.) and no-alpha with a decrease (9.2 to 0.1 ft c.). F is the same except the increase was 1.6 to 10.0 ft c. and the decrease 10.0to 1.6 ft c.

mination and attention used in this study, a result which might not be generalized to larger increments or more intense stimulation (Cruikshank 1937). During steady stimulation, a series of ONl (alpha) and ONe (no.alpha) events occurred. ON~ (no-alpha) durations exhibited a decrease which was fitted by a hyperbolic function of serial position of the event while ONt (alpha) with a linear function of serial position. The changes in the durations of successiveoccurrences and non-occurrences of EEG alpha, observed and termed by Bagchi (1937) *'intermittent adaptation", are generally similar to the changes of ONz (alpha) and ONe (no-alpha) events recorded during feedback stimulation. This similarity of conical response to both steady, and changing, feedback stimulation sugDISCUSSION gests the hypotheses that the process of activation The resultsshow that the initiationand habi. by steady stimulation may also be a feedback tuation of cortical activation is non-specific for process. Cortical response to steady stimulation the direction of stimulus change and for the in- may alternate between activation and deactivatensity oi"ti,~stimulus. This permits the designa- tion which are linked to inhibition and facilitation of cortical activation by a feedback stimulus tion, respectively, of input to the reticular activatas a component of orienting reflexas defined by ing system forming a servo-loop (Voronin and Soko|ov (1963). The lack of definite differences Sokolov 1960; Hernlndez Pebn 1960). The exterbetween levels of il:umination during feedback nal loop described here could interact with such may reflect the particular combination of illu- an internal loop to accentuate or attenuate proElectroenceph, olin. Neurophysiol,, 1964, 17:371-375

EEG AND VISUALSTIMULATION cesses already occurring in response to continuing stimulation. SUMMARY Cortical activation in response to increments and decrements was evaluated using a stimulusbrain response feedback loop. For one group of subjects an increment o f illumination occurred when a!pha occurred and the reverse decrement when activation occurred. For the other group, a decrement of illumination occurred when alpha occurred and the reverse increment when activation occurred. There was no significant difference between the two groups with regard to latencies and durations o f successive activation responses. During feedback and a prior steady illumination condition, successive group average indices o f alpha and no-alpha durations were approximated by a linear and hyperbolic function, respectively, o f number o f p r i o r alpha and no-alpha events.

375 REFERENCES

BA~II, B. K. The adaptation and variability of response of the human brain rhythm. J. Psychol., 193/, 3: 463485. CRUIK.~'IANK,R. M. Human occipital brain potentials as affected by intensity-duration variables of visual stimulation. J. exo. Ps.vchol.o1937, 21: 625-641. H~ZNANDF,z-P~N, R. Nedrophysiological correlates of habituation and other manifestations of plastic inhibition (internal inhibition). Electroenceph. clin. Neurophy$iol., 1960, Suppl. 13:101-114. MULHOLLAND,T. and RUNNALS,S. Evaluation of attention and alertness with a stimulus-brain feedback loop. Electroenceph. din. Neurophysiol., 1962,14: 847-852. SOKOLOV,E. N. Higher nervous functions: the orienting reflex. Ann. Rev. Physiol., 1963, 25: 545-580. VORONtN,L. G. and SOKOLOV,E. N. Cortical mechanisms of the orienting reflex and its relation to the conditioned reflex. Electroenceph. din. Neurophysiol., 1960, Suppl. 13: 335-346.

Reference: MULHOLLAND,T. and RUNNALS,S. Cortical activation during steady and changing visual stimulation. Electroenceph, din. NeurophysioL , 1964,17: 371-375.