Elec~oencephalography and Clinical Neurophysiology, 1978, 45:731--739

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© Elsevier/North-Holland Scientific Publishers, Ltd.

VISUAL E V O K E D P O T E N T I A L IN MAN: E A R L Y O S C I L L A T O R Y P O T E N T I A L S i ROGER Q. CRACCO and JOAN B. CRACCO Department of Neurology, State University of New York, Downstate Medical Center, Brooklyn, N. Y. 11203 (U.S.A.)

(Accepted for publication: May 2, 1978)

Short latency au d i t or y and somatosensory averaged evoked potentials which arise in subcortical areas have been recorded from the human scalp (Jewett et al. 1970; Cracco and Cracco 1976). Similar potentials evoked by visual stimulation have n o t been described in man. In animals, however, a series of short latency visual evoked oscillatory potentials have been recorded from the optic nerve, tract, lateral geniculate body, optic radiation and visual co r tex ( D o t y and Kimura 1963; D o t y et al. 1964; Hughes 1964; Steinberg 1966; Steriade 1967, 1969). In this communication similar scalp-recorded evoked potentials in man are described.

Methods and materials Observations were made on 15 normal volunteer subjects (5 male, 10 female) ranging in age from 18 to 45 years. Recordings were p e r f o r m e d with subjects seated in a comfortable reclining chair or lying supine on a bed in a dimly lit r o om . Bright light flashes (duration 10 psec) were delivered to bot h eyes by a Grass PS22 photic stimulator (intensity setting 16) which was placed 20 cm in f r o n t of the subject's nasion. In all but the

1 This investigation was supported by Research Grant NS12039 from the National Institutes of Health, U.S. Public Health Service. A preliminary report of these results was presented at the annual meeting of the American Electroencephalographic Society in Miami, Fla., June 24, 1977.

first 6 subjects studied, recordings were perf o r m e d with the stroboscope enclosed in a double-walled foam rubber air insulated encasement to minimize audible lamp click. Flashes were usually delivered at a rate of 2/sec but rates of 5/sec and 7.5/sec were also used. Control recordings in which no light stimulus was delivered were also perform ed. In these experiments the lamp was covered with a light opaque cardboard disc. Recordings were perform ed with t he subject awake and with eyes closed. Recording electrodes (6 mm diameter tin discs) were attached to the scalp with collodion and filled with conductive jelly. Elect rode impedance was maintained between 1500 and 3000 ~2. In all subjects these were placed along the midline usually at the FPz, Fz, Cz, Pz and Oz placements of the International 10--20 system. Recording electrodes were similarly attached to the left or right ear and, in 4 subjects, to the dorsum of the left or right hand. Scalp-ear reference recordings were p e r f o r m e d in all subjects. Scalp-hand reference recordings were obtained in 4 subjects. Additionally, in 4 subjects, bipolar recordings were obtained from electrodes placed below and at the o u t e r canthus of one eye and ear reference recordings were obtained from electrodes placed over the posterior mid and lower neck. In 3 subjects the effect of differences in light intensity and the effect of m o n o c u l a r versus binocular stimulation on the evoked response recorded in scalp midline (FPz to Oz) ear reference leads was investigated. In these

732 subjects responses recorded with Grass PS22 photic stimulator intensity settings of 4 and 16 were obtained and compared and the response evoked by stimulating the left and right eye independently was com pa r ed with the response obtained with binocular stimulation. A light opaque cloth was placed over the unstimulated eye. In 3 subjects the scalp distribution of the evoked response was investigated. Recording electrodes were attached at all standard scalp placements of the International 10--20 system except Ts and T6 and left or right ear reference recordings were obtained. Left and right ear recordings referenced to one shoulder or to the dorsum of one hand were also performed. In 3 subjects the effect of muscle tension on the scalp recorded response was studied in an a t t e m p t to differentiate cerebral activity from evoked myogenic responses (phot o m o t o r response) (Bickford et al. 1964). In these subjects scalp midline recording electrodes (FPz to Oz) were applied and ear reference recordings were performed. Tension was applied to the neck extensors by applying 10 lb to the back of the head in a forward direction by a plastic loop and pulley arrangem e n t to which the weight was applied. In separate experiments tension was applied to the frontalis muscles by recording while the subject was asked to wrinkle his forehead. Responses recorded during muscle tensing maneuvers were compared with responses obtained when the subject was relaxed. Potentials were judged to be myogenic if they were recorded only with muscle tension or were markedly augmented by it (Cracco and Bickford 1968). Input from 4 leads at a time was summated by a c o m p u t e r and written out by an X-Y p l o t t e r 2. Routinely, 1024- - 2048 responses were summated. Analysis times of 60--120 msec were used but attention was focused on potentials occurring within the first 60 msec. ~IDetai~ of the instrumentation used can be obtained by writing to the authors.

R.Q. CRACCO, J.B. CRACCO The frequency response of the recording apparatus was usually 100--2500 c/sec (--3 dB) but in 3 subjects responses were also obtained with a frequency band-width of 1--2500 c/sec. The c o m p u t e r horizontal sampling time was 60--120 psec per point with 256 points on each of 4 channels. The sampling time on each channel was 240--480 psec (digitizing frequency 4167--2084 c/sec). Two or 3 recordings were superimposed to differentiate time-locked from random activity and to demonstrate the reliability of the observations.

Results The evoked response to bright light flash stimulation consisted of a series of potentials which were usually oscillatory in configuration. These potentials were distributed widely over the scalp (Fig. 1). The onset latency of the response recorded over anterior frontal regions ranged between 9 and 17 msec and the peak latency of the first potential ranged between 11 and 21 msec. The oscillations persisted for up to 90 msec after the stimulus. Over central-parietal-occipital regions the onset latency ranged between 13 and 24 msec and the peak latency of the first potential ranged between 15 and 27 msec. The oscillations persisted for over 100 msec after the stimulus in some subjects. The frequency of these oscillations were usually 100--160 c/sec over anterior head regions and 80--170 c/sec over posterior head regions. The durations of the later wavelets recorded over posterior head regions were greater than those of the earlier oscillations in some subjects. These potentials showed considerable variability in configuration and amplitude both within and across subjects. However consistent responses were obtained in each subject during a single recording session. Scalp-ear reference and scalp-hand reference leads yielded similar potentials except that in two subjects studied early in the investigation a biphasic potential with peak

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Fig. 1. Scalp distribution of the early visual evoked oscillatory potentials recorded in left ear reference leads. Two averaged responses are superimposed in each trace. Oscillatory potentials are apparent at each scalp recording location. They are more prominent in midline and parasagittal leads than in temporal leads. At FP z the first potential is negative and peaks at 14 msec (N14). This is followed by P18, N2z, P24, N28, P33, N36, P39, N42 and Pso potentials. In the Oz lead, P21, N2 s, P30, N34, P39, N4s, Ps 2 and Ns s potentials are prominent (subject E.P.).

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msec. 0 60 0 60 Fig. 2. Left traces show scalp midline left ear reference recordings of the response to bright light stimulation. Right traces were obtained when the photic stimulating lamp was masked with a light opaque cardboard disc. Two recordings are superimposed in each trace. A small upward deflection peaking at 15 msec followed by a poorly defined downward deflection is apparent in the traces performed when no light stimulus was delivered (subject D.S.).

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R.(Q. CRACC, O, J.B. CRACCO

latencies of about 15 and 20 msec was recorded in scalp-ear leads. This component was n o t apparent in scalp-hand leads but was recorded in ear-hand leads and in control recordings where no light flash stimulus was delivered (Fig. 2). This response was interpreted as being the auditory evoked post auricular response recorded by the ear electrode (Bickford et al. 1964; Streletz et al. 1977), the auditory stimulus being the 'click' generated by the gas discharge of the photic stimulator. This potential was not observed in any subject when the photic stimulator 'click' was diminished by encasing the stroboscope. Control recordings where no light stimulus was delivered and ear-hand leads otherwise yielded no response. The oscillatory potentials were widely dis-

tributed over the scalp and were observed at all scalp recording locations (Fig. 1). They were always greater i~ amplitude at midline and parasagittal recording locations than in temporal leads. The first few oscillatory potentials were similar in amplitude in central parietal and occipital leads and were lower in amplitude than subsequent potentials. In some subjects the subsequent oscillations were similar in amplitude at central, parietal and occipital recording locations while in others they were more prominent in occipital leads. The potentials recorded in anterior frontal leads were often greater in amplitude than they were at other scalp recording locations. Similar potentials were recorded from a bipolar lead which linked a site below an eye to the outer canthus.

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Fig. 3. Comparison of the response evoked by monocular and binocular stimulation. Two recordings are superimposed i n each trace. With m o n o c u l a r stimulation the response amplitude is smaller (subject N.C.).

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Fig. 4. E f f e c t o f d i f f e r e n t low linear f r e q u e n c y filters o n t h e e v o k e d p o t e n t i a l s r e c o r d e d in left ear r e f e r e n c e leads. T w o r e c o r d i n g s are s u p e r i m p o s e d in each trace. T h e small o s c i l l a t o r y p o t e n t i a l s seen at FPz w i t h a low f r e q u e n c y filter s e t t i n g o f 1 0 0 c/sec are a p p a r e n t as p o o r l y d e f i n e d i n f l e c t i o n s s u p e r i m p o s e d o n t h e slow E R G waves s e e n in r e c o r d i n g s perf o r m e d w i t h a s e t t i n g o f 1 c/sec. T h e slower p o t e n tials r e c o r d e d at O z in r e c o r d i n g s p e r f o r m e d w i t h a filter s e t t i n g o f 1 c/sec are n o t a p p a r e n t w i t h a s e t t i n g o f 1 0 0 c/sec {subject A.M.).

Monocular stimulation elicited potentials which were usually about half the amplitude of potentials evoked by binocular stimulation (Fig. 3). In some subjects certain components were not apparent with monocular stimulation. A similar reduction in response amplitude was observed when the stimulus intensity was reduced. With low frequency filter settings of 1 c/sec, the occipital oscillatory potentials were superimposed on slower potentials which were n o t evident when recordings were performed with the 100 c/sec low frequency setting. Oscillatory potentials at anterior frontal locations were often obscured at low frequency settings of 1 c/sec where they appeared as peaks or inflections superimposed on the large slow potentials of the electroretinogram which have been described by Allison et al. (1977} (Fig. 4}.

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0 60 ms~ 0 '6o Fig. 5. E f f e c t o f m u s c l e t e n s i o n o n o s c i l l a t o r y p o t e n tials r e c o r d e d in scalp m i d l i n e left ear r e f e r e n c e leads. T h r e e recordings are s u p e r i m p o s e d in each trace. T e n s i o n in t h e n e c k e x t e n s o r s does n o t signific a n t l y alter t h e response. T e n s i o n in t h e f r o n t a l i s muscles elicits r a n d o m m y o g e n i c activity a n d a t i m e l o c k e d e v o k e d p o t e n t i a l at FP z w i t h a p e a k l a t e n c y o f 48 m s e c {bracket) w h i c h is n o t a p p a r e n t w h e n t h e s u b j e c t is relaxed ( t o p traces, s u b j e c t B.S.; b o t t o m traces, s u b j e c t B.V.).

The oscillatory potentials recorded from posterior scalp locations were n o t recorded from electrodes placed at posterior nuchal locations and these potentials were n o t significantly altered in experiments where tension was applied to the neck extensors (Fig. 5). Potentials recorded at anterior frontal locations were n o t enhanced when tension was applied to the frontalis muscles but a potential with a peak latency of about 50 msec was recorded in one subject when tension was applied to the frontalis muscles which was n o t evident in recordings performed when the subject was relaxed (Fig. 5). This potential observed only with muscle tension was judged to be myogenic in origin.

736 Discussion

In cats, the evoked response in visual cortex to electrical stimulation of the optic tract consists of a series of 4 positive potentials each about 1 msec long (1000 c/sec) followed by longer negative and positive potentials (Bishop and Clare 1951, 1952, 1953; Malis and Kruger 1956), The first two potentials are thought to arise in two different fiber groups in the optic radiations having different conduction velocities. The subsequent potentials are believed to reflect mainly intracortical postsynaptic activity. In the monkey, only two primary positive deflections occur (Doty et al. 1964). A series of short latency oscillatory potentials, similar to those observed in this study, have been recorded following bright light flash stimulation from the optic nerve, tract, lateral geniculate body, optic radiation and visual cortex of cats and primates (Granit 1933; Doty and Kimura 1963; Hughes 1964; Steinberg 1966; Steriade 1967, 1969). In monkeys, the optic tract response begins as early as 10 msec after the stimulus and has a frequency of about 100--150 c/sec (Doty and Kimura 1963; Doty et al. 1964; Steinberg 1966). The latency of the geniculate response is 3 - 6 msec longer than the tract response and is similar to the latency of the response recorded over the optic radiations and visual cortex which ranges between 16 and 30 msec (Doty et al. 1964; Hughes 1964). In monkeys, the frequency of the oscillations over optic radiations and striate cortex is very variable but averages about 130 c/sec and 180 c/sec, respectively (Doty et al. 1964; Hughes 1964). Over striate cortex these potentials are more prominent in monkeys than in cats. In man, the visual evoked potential to flash stimulation has been recorded by many investigators and found to have variable wave form characteristics. This variability reflects differences in stimulating and recording technique and differences in dark adaptation. In midline occipital-parietal leads, Ciganek (1961 ) reported that the onset latency of the

R.~. CRACCO, J.B. CRACCO response was about 28 msec. Responses occurring in the first 80 msec consisted of occipital negative, positive and negative components with peak latencies of about 39, 53 and 73 msec which he thought arose in the visual cortex. After 250 msec the response was characterized by slow oscillatory potentials with a frequency of about 10 c/sec which are thought to be related to the alpha rhythm. Cobb and Dawson (1960), recording with bipolar leads over posterior head regions, reported an onset latency of 20--22 msec with occipital positive, negative and positNe potentials peaking at about 28, 40 and 65 msec, respectively. These investigators also found 100 c/sec oscillatory potentials superimposed on slower potentials but these oscillations were not apparent within the first 50 msec of the response. Similar oscillatory potentials whose latency ranged from about 35 to 90 msec were recorded from posterior scalp leads and from striate cortex by Vaughan and Hull (1965) and Vaughan (1966). Allison et al. (1977), in scalp ear reference leads, recorded early positive, negative, positive, negative and positive potentials peaking at about 40, 55, 60, 70 and 80 msec which they thought were cortical in origin. These investigators also recorded a series of oscillatory potentials, similar to those reported here, from occipital leads whose latency ranged between 60 and 100 msec. In the present study stimulating and recording methods thought to be optimal for recording the early oscillatory potentials recorded over the optic system of animals were employed. Bright flashes at rapid stimulus rates were employed since these responses are strongly enhanced in animals with sustained light adaptation which is produced by the rapid repetition rate of the stimulus (Steinberg 1966). The slower evoked potentials were filtered so that the fast oscillatory potentials would be more clearly defined and m a n y responses were summated so that small potentials could be detected. Responses recorded over anterior frontal regions and from leads around the eye con-

SHORT LATENCY VISUAL EVOKED POTENTIALS IN MAN

sisted of a series of oscillatory potentials with a frequency of a b o u t 100--160 c/sec which began a b o u t 12 msec after the stimulus and persisted for up to 90 msec. The source of these potentials is uncertain. These potentials were not significantly affected by tension in the frontalis muscles which suggests they are n o t evoked myogenic responses arising in the frontalis muscles. Additionally, the latencies of the earlier of these potentials were less than those of p h o t o m o t o r responses (Bickford 1964). Allison et al. (1977) have recorded negative, positive, positive and negative potentials with peak latencies of a b o u t 20 msec, 50 msec, 65 msec and 80 msec from leads around the eye which they identified as the electroretinogram (ERG) a wave, x wave, b wave and after-potential, respectively. Although these ERG c o m p o n e n t s probably contribute to the response recorded over anterior frontal regions in the present study, they cannot be the primary source of these potentials because their latency and wave form characteristics are different. Using similar stimulating methods, well defined oscillatory potentials with similar latency and wave form characteristics to those recorded over anterior frontal regions in the present study have been recorded from the optic nerve and tract of animals (Doty and Kimura 1963; D o t y et al. 1964; Steinberg 1966). Oscillatory potentials which are similar in latency and wave form have also been recorded from the ERG of animals and man (Granit 1933; Cobb and Morton 1953; Cobb and Dawson 1960; Y o k o y a m a et al. 1964). These ERG oscillatory potentials are thought to be generated by the membranes of the inner plexiform layer of the retina involving the axon terminals of the bipolar cells, the processes of the amacrine cells and the dendrites of the ganglion cells (Ogden 1973). However, under the conditions of sustained light adaptation used in this study, Steinberg (1966) found that the optic nerve and tract response recorded in cats was maximal b u t the ERG oscillatory potentials were attenuated and were n o t consistently recorded in

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different preparations. Additionally, the prolonged duration of the oscillatory potentials recorded over anterior head regions in a few subjects is characteristic of the oscillatory potentials recorded from the optic nerve and tract in animals b u t is greater than the duration of ERG oscillatory potentials recorded in animals and man (Cobb and Morton 1953; Y o k o y a m a et al. 1963; D o t y and Kimura 1963; D o t y et al. 1964). Therefore, on the basis of present available information, it is probable that the oscillatory potentials recorded over anterior frontal regions arise, at least in part, in anterior optic pathways including the optic nerve and tracts. The ERG probably also contributes to this response. The earlier oscillatory potentials recorded over posterior head regions were similar in amplitude over central, parietal and occipital regions b u t the later potentials were more prominent over occipital regions in some subjects. This distribution is n o t consistent with an origin in the ERG. These potentials were n o t enhanced by muscle tension and were not recorded over the neck. These observations suggest that these potentials are n o t myogenic in origin ( p h o t o m o t o r response). The fact that these potentials were n o t recorded when the light flash was masked and were markedly attenuated with monocular stimulation and with decreased stimulus intensity make it unlikely that these potentials were due to non-physiological artifact. Their short onset latency of 13--24 msec and their frequency of a b o u t 100 c/sec is similar to the visual evoked oscillatory potentials recorded from the lateral geniculate b o d y , optic radiation and cortex of animals. It seems likely that these potentials arise in these structures. The mechanism which underlies the genesis of these oscillatory potentials is uncertain. It is possible that they reflect a series of components which arise in sequential neural elements. However, in animals, the oscillatory potentials of the optic tract population response are represented at the unit level b y grouped discharges of retinal ganglion cells

738 whose inter-group p e r i o d is identical to t h a t o f the p o p u l a t i o n response (Crapper and Noell 1963; D o t y and K i m u r a 1 9 6 3 ; Yokoy a m a e t al. 1964; Steinberg 1966). This suggests t h a t the optic nerve and t r a c t p o p u l a t i o n response is p r o d u c e d by the s y n c h r o n o u s discharge o f ganglion cells. These oscillatory p o t e n t i a l s are t h o u g h t to be p r o p a g a t e d to cortical s t r u c t u r e s ( D o t y et al. 1964). Corticothalamo-cortical, intraretinal, intrathalamic and intracortical circuits and the afterdischarge o f cortical n e u r o n s , m e m b r a n e oscillations and dendrite-cell b o d y circuits have all been implicated in the genesis o f the oscillat o r y potentials r e c o r d e d over visual c o r t e x {Chang 1 9 5 0 ; Clare and Bishop 1955; Crapper and Noell 1 9 6 0 ; D o t y and G r i m m 1962; Hughes 1964). T h e significance of these potentials is questionable. T h e y m a y be an e p i p h e n o m e n o n w i t h o u t f u n c t i o n a l significance. H o w e v e r , it is possible t h a t these wavelets carry c o d e d inform a t i o n which is of value to the r e s p o n d i n g organism or t h e y m a y be involved in setting the state o f general excitability o f the visual system.

R.Q. CRACCO, J.B. CRACCO R~sum~

Potentiels dvoquds visuels chez potentiels oscillatoires prdcoces

l'homme:

Les p o t e n t i e l s dvoqu6s visuels de c o u r t e latence ~ des stimulations de lumi~re brillante oscillatoire o n t ~t~ enregistr~s sur le scalp chez 15 sujets adultes n o r m a u x . Les latences de d 6 b u t de ces p o t e n t i e l s enregistr~s sur les r~gions frontales ant~rieures et sur les r~gions post6rieures s o n t r e s p e c t i v e m e n t de 9--17 msec et 1 3 - - 2 4 msec. La f r 5 q u e n c e des oscillations est d ' e n v i r o n 100 c/sec. Ces p o t e n t i e l s o n t une large distribution sur le scalp mais pr~d o m i n e n t au niveau de localisations d'enregistrements m~dianes et parasagittales. C o m m e les potentieIs similaires enregistrds chez l'animal, il semble que ces p o t e n t i e l s p r e n n e n t naissance dans les s t r u c t u r e s visuelles sous-corticales et corticales. Les auteurs d i s c u t e n t le m~canisme sous-jacent fi la prod u c t i o n de ces p o t e n t i e l s et leur signification f o n c t i o n n e l l e possible.

References

Summary S h o r t l a t e n c y visual e v o k e d oscillatory potentials to bright light stimulation were r e c o r d e d f r o m the scalp o f 15 n o r m a l h u m a n adult subjects. T h e o n s e t latencies of these potentials r e c o r d e d over a n t e r i o r f r o n t a l and p o s t e r i o r scalp regions were 9 - - 1 7 msec and 1 3 - - 2 4 msec, respectively. T h e f r e q u e n c y o f the oscillations was a b o u t 100 c/sec. These p o t e n t i a l s were widespread in their distribution over the scalp b u t were m o s t p r o m i n e n t at midline and parasagittal r e c o r d i n g locations. Like similar potentials r e c o r d e d in animals, it seems t h a t these p o t e n t i a l s arise in b o t h subcortical and cortical visual structures. T h e m e c h a n i s m u n d e r l y i n g the g e n e r a t i o n o f these p o t e n t i a l s and their possible f u n c t i o n a l significance are discussed.

Allison, T., Matsumiya, Y., Goff, G.D. and Goff, W.R. The scalp topography of human visual evoked potentials. Electroeneeph. olin. Neurophysiol., 1977, 42: 185--197. Bickford, R.G. Properties of the photomotor response system. Electroeneeph. olin. Neurophysiol., 1964: 17: 456. Bickford, R.G., Jaeobson, J.L. and Cody, D.T. Nature of average evoked potentials to sound and other stimuli in man. Ann. N.Y. Acad Sci., 1964, 112: 204--223. Bishop, G.H. and Clare, M.H. Radiation path from geniculate to optic cortex in cat. J. Neurophysiol., 1951, 14: 497--505. Bishop, G.H. and Clare, M.H. Sites of origin of electric potentials in striate cortex. J. Neurophysiol., 1952, 15: 201--220. Bishop, G.H. and Clare, M.H. Response of cortex to direct electrical stimuli applied at different depths. J. Neurophysiol., 1953, 16: 1--19. Chang, H.T. The repetitive discharges of corticothalamic reverberating circuits. J. Neurophysiol., 1950, 13: 235--257. Ciganek, L. The EEG response (evoked potential) to

SHOI~T LATENCY VISUAL EVOKED POTENTIALS IN MAN light stimulus in man. Electroenceph. clin. Neurophysiol., 1961, 13: 165--172. Clare, M.H. and Bishop, G.H. Dendritic circuits: the properties of cortical paths involving dendrites. Amer. J. Psychiat., 1955, 111: 818--825. Cobb, W.A. and Dawson, G.D. The latency and form in man of the occipital potentials evoked by bright flashes. J. Physiol. (Lond.), 1960, 152: 108--121. Cobb, W.A. and Morton, H.B. A new c o m p o n e n t of the human electroretinogram. J. Physiol. (Lond.), 1953, 123: 36--37P. Cracco, R.Q. and Bickford, R.G. Somatomotor and somatosensory evoked responses: median nerve stimulation in man. Arch. Neurol. (Chic.), 1968, 18: 52--68. Cracco, R.Q. and Cracco, J.B. Somatosensory evoked potential in man: far field potentials. Electroenceph. clin. Neurophysiol., 1976, 41: 460--466. Crapper, D.R. and Noell, W.K. Retinal responses to direct electrical stimulation. Physiologist, 1960, 3: 42P. Crapper, D.R. and Noell, W.K. Retinal excitation and inhibition from direct electrical stimulation. J. Neurophysiol., 1963, 26: 924--947. Doty, R.W. and Grimm, F.R. Cortical responses to local electrical stimulation of retina. Exp. Neurol., 1962, 5: 319--334. Doty, R.W. and Kimura, D.S. Oscillatory potentials in the visual system of cats and monkeys. J. Physiol. (Lond.), 1963, 168: 205--218. Doty, R.W., Kimura, D.S. and Mogenson, G.J. Photically and electrically elicited responses in the central visual system of the squirrel monkey. Exp. Neurol., 1964, 10: 19--51. Granit, R. The components of the retinal action potential and their relation to the discharge in the optic nerve. J. Physiol. (Lond.), 1933, 77: 207-240. Hughes, J.R. Responses from the visual cortex of

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unanesthetized monkeys. Int. Rev. Neurobiol., 1964, 7: 99--152. Jewett, D.L., Romano, M.N. and Williston, J.S. Human auditory evoked potentials: possible brain stem components detected on the scalp. Science, 1970, 167: 1517--1518. Malis, L.I. and Kruger, L. Multiple response and excitability of cats visual cortex. J. Neurophysiol., 1956, 19: 172--186. Ogden, T.E. The oscillatory waves of the primate electroretinogram. Vision Res., 1973, 13: 1059-1074. Steinberg, R.H. Oscillatory activity in optic tract of cat and light adaptation. J. Neurophysiol., 1966, 29 : 139--156. Steriade, M. Effets potentiateurs sp4cifiques de l'illumination continue sur les r~ponses ~voqu~es au niveau du cortex visuel par des stimuli p~riph~riques et centraux. In: A.M. Monnier (Ed.), Actualit4s Neurophysiologiques, Vol. 7. Masson, Paris, 1967: 109--139. Steriade, M. Physiologie des Voies et des Centres Visuels. Masson, Paris, 1969. Streletz, L.J., Katz, L., Hohenberger, M. and Cracco, R.Q. Scalp recorded auditory evoked potentials and sonomotor responses: an evaluation of components and recording techniques. Electroenceph. clin. Neurophysiol., 1977, 43: 192--206. Vaughan, H.G. The perceptual and physiologic significance of visual evoked responses recorded from the scalp in man. In: Clinical Electroretinography (Suppl. Vision Res.). Pergamon Press, Oxford, 1966: 203--223. Vaughan, H.G. and Hull, R.C. Functional relation between stimulus intensity and photically evoked cerebral responses in man. Nature (Lond.), 1965, 206: 720--722. Yokoyama, M., Kazumasa, K. and Yoshimasa, N. The oscillatory potential in the retina and optic nerve of rabbit. Mie med. J., 1964, 13 : 109--122.

Visual evoked potential in man: early oscillatory potentials.

Elec~oencephalography and Clinical Neurophysiology, 1978, 45:731--739 731 © Elsevier/North-Holland Scientific Publishers, Ltd. VISUAL E V O K E D P...
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