American electroencephalographic society

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Electroenccphalography and Clinical Neurophysiolog 3, 1975, 3,~': 542 556 Elsevier Scientific Publishing Company, Amsterdam Printed in The Netherlands

SOCIETY

PROCEEDINGS

A M E R I C A N E L E C T R O E N C E P H A L O G R A P H I C SOCIETY Seattle. Washington. July 25 27, 1974 Pro,qram Chairman:

D R . G . E. CHATRIAN

l)~rision o~ EEG and Clinical Neuroph.rsiolo~ly, NN283 l_:niversil), Hospital, SB-I O, Seattle, f l a s h 98195 ( U.S. 4 ,

Timing of averaged movement potentials and articulatory events: An EEG, EMG and cineradiographic study.---G. Zimmermann, J. R. Knott, M. Mendel and D. Keuhn (Iowa City, Iowa). An electrocortical correlate of speech, described by M c A d a m and Whitaker, could be of significant clinical value. The adequacy of their methodology was questioned by Morrell and Huntington. The present authors felt that neither group sufficiently explored the possibility that some articulatory activity preceded the so-called "speech readiness potential'" Gerbrandt et al. recently reported that muscle action often preceded averaged movement potentials which had been hitherto thought to represent the initiation of upper motor neuron firing, The present study investigated the relationships between slow cerebral potentials, articulatory movement, and articulatory muscle action in 6 normal speakers, using EEG. E M G and high speed cineradiographic recording techniques. Events described in each recording were measured from the onset of voicing measured by a laryngeal microphone, these being velar movement, lip movement, jaw movement, onset of muscle activity in the superior orhicularis and DC potentials measured bilaterally from the scalp over Broca's area, its contralateral homologue and the vertex. Electrophysiological and cineradiographic data, separately recorded, were backaveraged from voice onset a n d superimposed. Our results show that palatal activity preceded voice onset by 200-400 msec, and motor potential by 100 msec. This is earlier than the brain potentials described by others.

2. Slow positive shifts during sustained motor activity in humans.--D. A. Otto and V. A. Benignus (Chapel Hill, N. C.). Kornhiiber and Deecke (1965) and others have reported a positive shift associated with the onset of movement. This waveform has usually been attributed to peripheral reafference, though the evidence is inconclusive. Otto and Leifer (1972) reported a prolonged positive shift, maximal postcentrally, during a 1 sec holding response without external cues. This positive shift could reflect reafference or a central

timing mechanism associated with estimating the temporal interval. This study was undertaken to distinguish between central timing and reafferent hypotheses. Slow potential changes during hand d y n a m o m e t e r pressing at force levels of 10, 25 and 50 "~ m a x i m u m for 1.3 and 5 sec intervals were investigated. Recordings were obtained at C3, C4, P3 and P4 with amplifiers modified to provide a 5 sec time constant. Signal averages were triggered from E M G onset recorded over the brachioradialis muscle of the responding arm. A negative shift was observed during time estimation without response, consistent with M c A d a m (1966). When sustained pressing was terminated by a stimulus (i.e.. response without time estimation) no consistent positive or negative shift was observed. Prolonged positive shifts were observed during non-cued pressing, although the amplitude and duration of the waveforms did not vary consistently with either the length or force of press.

3. The CNV in cases of hemispheric vascular lesions.J. Cohen (Chicago, Ill.). Forty patients who had suffered from hemispheric vascular lesions were tested for normality of the EEG, evoked potentials to auditory and visual stimuli and the contingent negative variation (CNV). A PDP-12 computer was used to analyze the data on- and off-line for average cerebral potentials and frequency analysis. Retests were done on 10 patients after intervals of 6 m o n t h s to 1 y e a r Thirty-six patients had been diagnosed as having left hemisphere lesions and were m a rehabilitation program for speech therapy. The EEGs were abnormal in over half of the patients, but the CNV was impaired in four-fifths of the group, generally being reduced on the side of the lesion. Either visual or auditory evoked potentials were also reduced in half of the patients, with more loss on the side of the lesion. We found that the CNV is a more sensitive indicator of cerebral cortical damage than the EEG, since in m a n y cases of C N V asymmetry and abnormality, the EEG was normal. There is a highly significant relationship between the CNV and speech improvement, and it can be seen from the retest data that the C N V is a good prognostic indicator for rehabilitation progress.

543

AMERICAN EEG SOCIETY 4. Responses of the human brain to electrical stimulation of tooth pulp.--G. E. Chatrian, R. C. Canfield, T. A. Knauss and E. Lettich (Seattle, Wash.). The pulp of individual teeth of 23 normal adult volunteers was stimulated with monophasic square pulses of 0.5 msec duration and 1.5 mA intensity delivered aperiodically at intervals of 2.54.9 sec via pairs of electrodes implanted in dentine. Typical tooth pulp-evoked potentials (TPEPs) were composed of two concurrent sequences of events. One, seen maximally over midline areas, characteristically consisted of four successive waves of alternating polarity, the first being negative relative to a suitable reference. The peak latencies of the third component were within the range of the negative "vertex wave" occurring in response to stimulation of most sensory systems. Another wave sequence consisted of one or two negative potentials which developed over the lower portion of the postcentral regions. Appropriate maneuvers demonstrated that TPEPs were not myogenic. Following mandibular block anesthesia, TPEPs could no longer be elicited from stimulation of the lower teeth. To the extent that TPEPs represent objective, quantifiable, non-verbal concomitants of central events associated with the perception of pain, they hold promise as a method of investigating acute experimental pain in man. Supported by U.S. Public Health Service Grant DE 03485. 5. Akinesia evaluated by amplitude reduction of somatic evoked responses. Its importance in prognosis of Parkinsonian patients treated by stereotaxic neurosurgery.-M. Velasco and F. Velaseo (Mexico, D.F., Mexico). Present report deals with changes in somatic evoked responses (SERs) and response velocity (RV) found after surgical treatment of 14 Parkinsonian patients with prominent unilateral tremor. Prior to operation 6 of these patients showed rigidity (detected by reduction in lineal movement velocity and increased spinal H reflex excitability) and 4 showed akinesia (detected by reduction in both RV and P5a SER component). In all patients, unilateral lesions circumscribed to the prelemniscal radiations were made by means of a leucotome oriented by the method of proportional reduction of human diencephalon (Velasco et al. 1973, 1974). Results were as follows: 1. Tremor was abolished and spasticity diminished in all patients after surgery. 2. Patients with no evidence of akinesia prior to surgery showed no significant changes in RV and P5a SER component with no additional sensory or motor deficits after surgery. 3. Patients with akinesia prior to surgery showed a further reduction in RV and P5a SER component after surgery. Other clinical signs of akinesia then became evident (slowness of movement, difficulties in station, oculomotor disturbances and alteration in vigilance). These results indicate that perceptual disorders of akinetic patients may be aggravated by surgical procedures. Therefore, preoperative detection of incipient akinesia by RV and SER determination has an important value in prognosis of candidates for stereotaxic neurosurgery. 6. Comparison of single and multiple peripheral nerve stimulation on the human spinal evoked potential.--R. Q.

Cracco and J. B. Cracco

(Brooklyn, N.Y.).

Summated evoked potentials to left or right peroneal nerve stimulation have been recorded from surface electrodes placed over the lumbar, thoracic and cervical spine of infants, children and adults. These responses progressively increase in latency rostrally and are thought to arise in the dorsal roots of the cauda equina and in spinal cord afferent pathways. It seems that this method might have application in some patients with spinal cord pathology. However, a major limitatation lies in the small size of these potentials, particularly in recordings over the rostral spinal cord. Evoked potentials to left or right peroneal nerve stimulation recorded in bipolar leads over the lumbar, thoracic and cervical spine were compared with similarly recorded responses to stimulation of multiple lower extremity peripheral nerves. Appropriate stimulus delays were employed with multiple nerve stimulation so that volleys arrived simultaneously over the lumbar spine. Responses to multiple nerve stimulation were similar in configuration but greater in amplitude and better defined at all recording locations than corresponding potentials evoked by single nerve stimulation. This was true for normal children, adults and a few patients with spinal cord pathology. 7. A physiological model for homologous displacement with paired rostral-caudal stimuli.--R. Cohn (Washington, D.C.). In rostra|-caudal double simultaneous tactile stimulation it is frequently observed that patients with decreased senticncy displace the caudal stimulus to the contralateral homologous rostral area of stimulation. A physiological model for this clinical phenomenon is presented. When various peripheral nerves are repetitivelystimulated and the summated evoked cortical responses (SECRs) are recorded bilaterally from homologous head regions the greater amplitude of response occurs on the contralateral hemisphere, but a contemporaneous similarly contoured pattern is produced ipsilaterally. Using small electrodes arrayed along the rolandic fissure to include differentially the face-hand and leg areas it is observed that the greatest amplitude of SECR is over the face-hand disposition. It has been demonstrated that amplitude, and not time of arrival, is the major determinant of perception in rostralcaudal applied paired stimuli: also with simultaneous ipsilateral stimuli the pattern of either the rostrally, or caudally, stimulated nerve dominated the resultant SECR contours. Thus the bilateral SECRs and the increased amplitude of response over the the face-hand area suggest that the rostral displacement is the result of a competition in which the contralateral "caudal" cortical activity suffers a deleterious interaction, and the ipsilatcral, ordinarily subliminal stimulus, reaches threshold. 8. Human auditory evoked sustained potentials.--T. W. Picton and D. L. Woods (La Julia, Calif.L An auditory stimulus will evoke from the human brain not only an onset vertex potential (N1-Pz) but also a negative baseline shift lasting the duration of the stimulus the "sus-

544 rained potenlial" (SP). Scalp distribution studies revealed that this auditory SP is maximally recorded from vertex and frontal head regions, being slightly more anterior than either the N j or P2 components. The scalpdistribution was independent of the ear stimulated, and there was no reversal of polarity across the Sylvian fissure. When tones lasting I sec were presented every 3 sec the intensity function of the SP was similar to that of the vertex potential although the SP t~as approximately one-half the amplitude of the baseline to N ~ measurement. The SP was. however, more resistant to decreasing interstimulus interval than was the vertex potential: when the interval was decreased from l0 to I sec the SP was decreased by 40 o, but the N, component by 80 ,,,. Both the vertex potential and the SP were smaller to higber frequency tonal stimuli, even when the tones were of equal loudness. The SP was clearly recordable during sleep, therefore suggesting that it is different from the contingent negative variation (CNV). Paying attention to the duration of repeating tone bursts in order to detect an occasional lone of long duration significantly increased the amplitude of the SP. However. it is diffictdt to determine whether this reprc,,ents an actual enhancement of the audflor3 SP or the concomitant generation of an attention-related stow potential such as the C N V

9. Averaged auditory-evoked potentials in normal children from 10 days to 3 years of age.--A. B. Barnet, E. S. Ohlrich, I. P. Weiss and B. L. Shanks (Washington,

D.C.). fhc averaged auditory evoked [:ECi potentials (AEPs) of 140 normal children from I0 days to 3 years of age tested during nat ural sleep were compared to investigate maturational changes and to provide normative data for the AEPs. Sets of 100 clicks of moderate intensity were presented to the sublects who were divided into 14 groups according to age. The AEP (I sec post-stimulus) was obtained using an electrode at the vertex referred to combined mastoids. Several major AEP waves displayed statistically significant overall decreases in latency and increases in amplitude with age, with the rate of change differing lor the various components. The latency of P2, for example, decreased from 217 msec at 15 days of age to 153 msec at 3 years, while N2 decreased from 483 to 325 msec in the same period. P2 N2 :tmplitude showed a corresponding increase from 24 to V. The morphology of the AEP also changed, reflecting a case in negativity at N I and the growing prominence of ~l~c late positive c o m p o n e n t P3. The utility of the AEP for diagnosis will be discussed, especially with respect to the variability of responses which were obtained in this study for normal children.

10. Evoked potential augmenting and reducing in psychiatric patients.--V. Milstein, J. G. Small, 1. F. Small and P. Sharpley (Indianapolis, Ind.). Several studies have related the amplitude/intensity slope of the visual evoked potential (VEP) to personality variables. Some investigators have found that this measure differentiates psychiatric patients and normal controls. Moreover, it has been reported recently that bipolar and unipolar

s o t i E f Y I'Rt)CEEI)IN(iS ['ornls o[ nlanic depres>,lVe disca~,c' a r e characterized h\ augmenting and reducing respectively These neurophysiological attributes may predict response to treatment with lithium and other drugs m such patients. Taken together, these observations could be interpreted to mean that there arc different kinds of CNS processing of sensory inputs m xarious mental illnesses, ttowever, the relative contribution of centrally cs peripherally mediated events to these phenomena has nol yet been clarified, For example, the influence of pupil size and potentials arising from corneo-retinal fields and orbital musculature needs to be examined before implicating mechanisms involving higher CNS ['unctions. We examined the amplitude/intensity slope of VEPs in more than 80 hospitalized psychiatric patients with various diagnoses. Averaged responses were elicited using four different intensities of light stimulation, before and after dilation of the pupils. Activity from midline occipital and ccnlral scalp placements and from periorbital areas wa~ averaged simultaneously Inspection of the data revealed that augmenting or reducing could depend upon which placement and peak amplitude was examined, both in the same and different patients. Further, averaged activity from the orbital areas likely contributed to the scalp response Additional data relating augmenting and reducing to psychiatnc diagnosis and drug treatment will be reported and the possible mechanisms underlying these phenomena will be discussed

I I. Cortical evoked potentials (CEPs) in agenesis of the corpus callosum.--Y. Matsumiya, C. T. Lombroso and G. Erba (Boston, Mass.). In 8 children and 2 adults with radiologicall3 proven agenesis of the corpus callosum, we observed a characteristic anolnaly in the long latency response to somatosensory. auditory, and visual stimuli while the short latency components were relatively intact. All subjects were symptomatic. namely with mental retardation or seizures or both: 7 ~ere on medication and 3 were not. Although these variables may account for some distortion of evoked potential waveform, all patients consistently exhibited extreme attenuation or absence of the vertex positive component which normally peaks at about 200 msec. This abnormality was most prominent for the somatosensory and least for the visual evoked potentials. These subjects may represent models to clarify the role played by the corpus callosum in various components ot h u m a n CEPs. For example, we found that long latency ipsilateral somalosensory responses were present in all cases. l h u s , these ipsilateral components were independent ,~l callosal transmission, contrary to some of the current interpretations. With the reservations imposed by the possible presence o f alternative pathways and the likelihood of other associated anomalies, these findings are reported because of their con sistency in spite of many variables including age, seizures and medications.

12. Flash-evoked potentials in migraine.--C. MacLean, 1. Cordaro, O. Appenzeller and J. M. Rhodes (Albuquerque, n.~1.).

AMERICAN EEG SOCIETY The electrical responses of the cortex to flashes presented to the eyes were recorded in 8 migrainous patients and 5 nonmigrainous controls. Four migrainous patients had classic migraine. All patients except 1 were tested both during a migrainous attack and during a headache-free interval. During the visual aura the hemisphere contralateral to the field defect showed suppression of the first 3 components of the visual evoked responses. In 2 of these patients, asymmetries were noted during headache-free intervals also. Patients with common migraine could not be differentiated from controls either during an attack or while headache-free. A computer program using an auto-regressive technique on resting records appears to achieve the same level of differentiation. However, the differentiation is based on a bandwidth measure with little effect seen from phase or mean frequency. It appears that either of these methods or a combined procedure might be useful in identifying patients with classic migraines and perhaps in monitoring the efficacy of headache remedies.

13. Effects of prophylactically administered dipheoylhydantoin on the development of chronic cobalt-induced epilepsy in the cat.--R. L. Rapport, II and G. A. Ojemann (Seattle, Wash.). Changes in several parameters of cobalt-induced experimental epilepsy in cats possibly related to diphenylhydantoin (DPH) prophylaxis were studied. These included behavioral manifestations of epilepsy, the onset and duration o f abnormal EEG discharges in focus and homotopic sensory-motor cortex, and alterations in sodium-potassium activated adenosine triphosphatase (ATP-ase)---an enzyme felt to be related to neuronal monovalent cation transport--in these same areas. The distribution of DPH in serum, cortex and cerebellum as a function of time following multiple dosing was also examined. Sham operated animals served as controls for both treated and untreated groups. The EEGs o f cobalt-implanted untreated cats showed paroxysms not present in records of animals started on DPH 4 h post-implantation or in control EEGs. The untreated animals also showed an increase in levels of ATP-ase which was significantly different from both treated and control cats between 8 and 28 days post-implantation. The increase in enzyme seemed to follow the appearance of EEG epileptic paroxysms during the maturation o f the focus. These findings suggest that DPH treatment prevents the appearance of both EEG and certain biochemical changes which accompany the epileptic process in this model. Furthermore, the EEGs and enzyme levels remained normal in animals which were treated with DPH for 4 weeks and then withdrawn.

14. Effect of electrical cerebeHar stimulation upon amygdaloid seizure and photosensitive seizure in subhuman primates.-J. A. Wada, T. Osawa and I. Cooper (Vancouver, B. C., Canada). Eight to 10 electrodes were implanted in the anterior surface of the cerebellum of both Senegalese baboon, Papio papio, and Rhesus monkey. Stimulation o f the cerebellum with different parameters varying from 20 to 200 c/sec and 3 to 11

545 V produced overt neurological manifestations such as generalized hypotonia, tilting o f head position, unmistakable calming effect as well as coarse tremor. There was a distinct tendency for these induced behavioral manifestations to become less prominent with prolonged stimulation so far lasting up to 11 h. Such electrical stimulation had no identifiable effect upon the electroclinical features of the well established amygdaloid kindled convulsion. Possible effects o f such stimulation upon amygdaloid kindling processes as well as photogenic seizure susceptibility are being examined at the present time.

15. Spontaneous recurrent generalized seizure state induced by daily amygdaloid stimulation in Senegalese baboon, Papio papio.-- J. A. Wada, T. Osawa and E. Jung (Vancouver, B. C., Canada). I n our previous amygdaloid kindling study in cats we reported the occurrence of recurrent generalized spontaneous seizures (Epilepsia (Amst.) in press), In this study the right amygdala of 4 Senegalese baboons, Papio papio, was chosen as the site of electrical stimulation with 200-2000 pA. 60 c/see sine waves delivered for 1 sec, once a day, 7 days a week. These animals were weakly photosensitive and had not manifested spontaneous seizures during 3 years o f observation prior to this study. The stimulation began 1 month after the implantation of 50-70 electrodes at various brain sites. All animals showed progress through a stage o f seizure development where the electroclinical manifestations were bilateral but asymmetrical. Presumably the same stage o f seizure development was reached in kindled rhesus monkeys (Goddard et al. 1969). However, our baboons have further progressed to the final stage of seizure development in which the electroclinical manifestations become bilaterally synchronous and symmetrical. In addition, 2 kindled baboons developed recurrent spontaneous seizures. Detailed examination of the spontaneous electroclinical seizures showed no focal or asymmetric features. This is in contrast to the spontaneous seizures in kindled cats in which the pattern of focal onset and march of ictal events were identical to or mirror images of the kindled seizures. We believe that the findings in Papio papio reflect a unique predisposition of this species toward primary generalized epilepsy. Detailed chronological study of electroclinical seizure development in presumably non-predisposed rhesus monkey is in progress for the purpose of comparison.

16. Evidence for cortical independence in experimental petit mal epilepsy.--S. C. Lange, G. W. Fowler and R. M. Julien (lrvine, Calif.). Studies on male and female cats were conducted using cortical application o f conjugated estrogen (CE) in order to further delineate the site of estrogen-induced 3/see spike-and-wave activity. 2 ~o CE was topically applied to intact and chronically isolated cerebral cortex and also injected into n. centrum medianum (CM) of the thalamus and into ventral and dorsal hippocampi. Injection of CE into subcortical structures produced generalized epileptiform activity characterized by intermittent bursts of high voltage polyspike complexes at 8-12/sec. Subcortical injection failed to elicit 3/see spike-and-

54(3 wave discharges. Unilateral application of CE to intact frontal cortex resulted in a generalized 3/see spike-and-wave pattern recordable in CM. Topical application of CE on intact frontal cortex with simultaneous CE injection into CM resulted in production of two independent seizure patterns occurring simultaneously: 3/sec spike-and-wave discharges originating from the cortex and 8-12/see polyspike pattern recorded in thalamus. Chronically isolated slabs of suprasylvian cortex were prepared in 5 animals. Topical application of CE to these slabs resulted in a 3/see spike-andwave pattern restricted to the isolated tissue. These studies reveal that CE initiates a 3/sec spike-and-wave pattern in cerebral cortex which may be recorded subcortically but participation of subcortical structures in CE induced 3/see spike-and-wave discharges appears to be unnecessary. Supported by U.S.Public Health Service Grant NS-09835 and by the Rebecca Payne Livingston Foundation. 17. Experimental models of "centrencephalic" epilepsy. EEG and multiple unit recordings.--E. Rodin, H. Kitano, S. Wasson and M. Rodin (Detroit, Mich.). Previous work from our laboratory has shown that m the cat, primary generalized tonic-clonic seizures produced by bemegride (Megimide) or pentylenetetrazol (Metrazol) originate in the lower brainstem rather than cortex or thalamus. The study was now expanded to include bicucullin a presumed inhibitor of G A B A - - a n d parenterai penicillin G, a model of petit mal epilepsy. Clinically, bicucullin produced myoclonic jerking, excitation and tonic-clonic seizures. The EEG suggested a cortical or thalamic onset, but the multiple unit record showed a pontine origin of the discharges. This finding agrees with the previous Metrazol Megimide data. Intramuscular penicillin produced a drowsy animal with only mild myoclonic twitching. The EEG showed at that time 1 to 2 sec episodes of 3-5/see spike-and-wave activity, most marked in cortex and thalamus. The multiple unit records showed distinct bursting type activity in these structures, but the bursts were not produced primarily by an excitatory, but by an inhibitory phenomenon. The pons remained uninvolved during these episodes. The findings suggest that the pathophysiologic mechanisms of generalized epilepsy should not be discussed under one term, be it "centrencephalic'" or "'cortico-reticular'L because different neurophysiological mechanisms appear to be involved in the various forms of that condition. 18. ExtraceHolur and intracellular electrography of spinal cord seizures.--E. Lothman and C. Somjen (Durham, N.C.). Convulsive activity was produced in spinal cords of unanesthetized, decapitated cat preparations by topical or intravenous penicillin. Electrical activity was recorded from skeletal muscle, peripheral nerves, dorsal and ventral roots, cord dorsum, and spinal gray matter, with both intra- and extracellular leads. Convulsive activity, whether occurring spontaneously or provoked by mild sensory stimuli, resembled the seizure patterns seen in epileptic forebrain. Accordingly, the activity may be classified as interictal and ictal, and the ictal subdivided into tonic and clonic (4--6/see) phases.

St )('IETY PRt)('EEI)[N(IS In non-paralyzed preparations, interictal events were marked by myoclonic jerks while tonic ictal events were associated with generalized muscular contractions lasting for several seconds. During clonic phases bursts of excitation produced phasic movements at a rhythm of 4- 6/sec. Afferent connections with periphery are not necessary for generation of either interictal or tonic clonic ictal events. Within the lumbosacral region the paroxysmal activity is synchronous among several segments. Convulsive activity is consistently associated with depolarizations of approximately 10 mV and multiple actio~ potential generation in motoneuronal somata, while the participation of interneurons in the convulsive activity is not obligatory. Even though concomitants of seizure activity are seen in dorsal roots and on the cord dorsum (Lothman and Somjen 1973), it appears that penicillin-induced spinal cord seizures originate and remain centered in ventral gray matter Supported by U. S. Public Health Service Grant NS 05330 and the Epilepsy Foundation of America. 19. Membrane changes in experimentally induced epileptic behavior.---T. Williamson and W. E. Crill (Seattle, Wash.). Although it is clear that in experimentally induced epilepsy there are changes in the synchronization and effect of synaptic inputs to single cells, indirect evidence suggests that there may also be alterations in the membrane ionic currents of single cells. To study this possibility in detail we have examined the effects of the convulsant drug pentylenetetetrazol (PTZ) on neurons of the isolated circumesophageal ganglia of Archidoris using current and voltage clamp techniques. Single cells were impaled with two microelectrodes, one for recording membrane potential and the other for passing current. When the perfusate contained 110 140 mM PTZ, spontaneous episodic prolonged depolarizations with superimposed high frequency spikes appeared within 5 10 min. This response could be evoked by intracellular stimulation and occurred with cell bodies isolated from their synaptic inputs by a ligature. Thus the responses seemed to occur independently of synaptic input. Voltage clamping before and after the application of PTZ revealed that PTZ caused a 5 10 mV reduction in resting potential associated with a decrease in leakage conductance by 33%. There was a substantial decrease in the steady state potassium conductance and a decrease in the transient outward current associated with depolarizations around the resting potential {the A current of Connor and Stevens). In order to determine the significance o fthese cond uctance changes in a relationship to the epileptic-like behavior, the response of the cell to an injected current pulse was calculated using the voltage and time dependent conductances measured under the voltage clamp experiments. The relationship of these calculated responses to the observed responses to current stimulation will be discussed. Supported by U.S.Public Heatlth Service Grant NS 07987 20. Stereotyped doublet and burst firing patterns in neurons or normal lateral cuneate nucleus: Evidence for a normal substrate for epileptic burst responses.-- E. H. Calvin and J. D. Loeser (Seattle, Wash.).

AMERICAN EEG SOCIETY Large depolarizing waves of synaptic origin (e.g., the paroxysmal depolarizing shift) may drive a normal neuron's depolarization-to-firing rate conversion mechanism to high firing rates. There is another normal mechanism which produces short interspike intervals: a depolarizing hump following a normal spike large enough to elicit an extra spike, thereby giving rise to a doublet firing pattern. These extra spikes sometimes generate additional extra spikes in a regenerative cycle, producing a high-frequency, stereotyped burst. Extracellular recordings from the cat lateral cuneate nucleus (LCN) often show cells which spontaneously discharge in doublets. In a given cell, these doublets show quite invariant timing, e.g., 0.8 _+0.1 msec between the spikes of the doublet. Additional spikes with a similar invariant interspike interval may be seen in some cells, e.g., triplets, bursts. When the receptive field of the cell is explored by natural stimulation, the doublet/burst firing pattern often suddenly disappears, i.e., the doublet/burst pattern seems to characterize only the low-level spontaneous activity of the cell. This is strikingly analogous to the doublets observed in spinal motoneurons (where the underlying depolarizing humps after spikes have been studied intracellularly) which occur only near the minimum rhythmic firing rates and which disappear as the depolarizing drive on the cell is increased. The stereotyped bursts of chronic epileptic foci seem analogous to the doublets/bursts in LCN ; we propose that "epileptic neurons" have augmented a normally latent regenerative firing mode. 21. Strychnine effects on excitatory synaptic transmission.-W. Raabe, E. Benassi, H. Dichter and G. F. Ayala (Minneapolis, Minn., and Genoa, Italy).

The effects of strychnine on excitatory synaptic transmission were investigated at the giant synapse of the squid stellate ganglion. Pre- and postsynaptic potentials were recorded by microelectrodes inserted into the pre- and postsynaptic axons close to the synapse. A third electrode, in the postsynaptic axon, permitted displacement of the transmembrane potential to obtain excitatory postsynaptic potentials (EPSPs) without superimposed action potentials. Strychnine (0.5 mM) had reversible effects on action potentials and the EPSP. The amplitude and after-hyperpolarization ofpre- and postsynaptic action potentials were decreased. In contrast, the amplitude of the EPSP was increased. Normally in this preparation the amplitude of the EPSP is directly related to the size of the presynaptic action potential. These observations point to a specific action of strychnine on mechanisms of excitatory synaptic transmission or on the subsynaptic membrane which results in increased EPSPs, even when simultaneously presynaptic action potentials are decreased. If strychnine has a similar action on EPSPs of the mammalian cortex, its epileptogenic effect, after topical application, could be partially based on increased excitatory synaptic coupling. 22. Intracellular recordings of rat caudate neurons with iontophoretic application of GABA and glycine.---G. Bernardi, V. Floris, M. G. Marciani and C. Morocutti (Rome, Italy).

lntracellular recordings of the effects of GABA and glycine

547 on caudate neurons of succinylcholine-immobilized rats were obtained. GABA and glycine were applied iontophoretically through electrodes with an inter-tip distance between recording and ejecting electrodes ranging from 50 to 100#. GABA (5~50 nA) hyperpolarized more than 9 0 ~ of tested neurons and decreased their membrane resistance as measured by current pulses. The "spontaneous" and evoked firing rate was blocked and the amplitude of EPSP-IPSP sequences evoked by cortical and endopeduncular stimulation clearly decreased. When the membrane was hyperpolarized by the injection of inward current, the iontophoretic application of GABA produced depolarization. Glycine blocked the firing rate of 40 ~ of neurons at doses 2~8 times higher than GABA. Glycine also hyperpolarized the cell and decreased the membrane resistance. Bicuculline (100-200 nA) antagonized the effect of GABA and glycine without blocking evoked IPSPs. Picrotoxin had similar effects but its action was less powerful than that of bicuculline. 23. The effect of tricyclic antidepressants on cortical inhibitory pathways.--G. H. Fromm and J. D. Glass (Pittsburgh, Pa.).

The corticofugal inhibition of afferent activity in the spinal trigeminal nucleus of cats is depressed by trimethadione (Tridione) and ethosuximide (Zarontin), and also by imipramine (Tofranil). A clinical trial showed that imipramine also is effective against petit real and minor motor seizures in some patients, thus confirming the validity of our experimental model for investigating the mechanisms involved in the production and control of petit mal seizures. We have now found that desipramine (Pertofrane) does not depress the corticofugal inhibition of the trigeminal nucleus of cats and that amitryptilene (Elavil) does so rather weakly. Although these drugs are chemically related to imipramine, one of them (desipramine) has a more marked adrenergic effect and the other (amitryptilene) has a more marked anticholinergic effect. In subsequent experiments, we found that the cortical inhibition of the trigeminal nucleus was significantly decreased when the anticholinergic drug procyclidine (Kemadrin) was injected at the same time as the desipramine, even though procyclidine by itself was even less effective than amitryptilene. These results suggest that the corticofugal inhibition in our experimental model is mediated by a cholinergic pathway which is itself subject to adrenergic inhibitory influences. 24. Sensitivity of brain tissue to intrinsic and-environmental oscillating electric flelds.--W. R. Adey (Los Angeles, Calif.).

Studies from this laboratory have shown altered behavior and neurophysiological responses and modified neurochemistry in weak environmental electric fields oscillating at EEG frequencies, and in weak VHF fields amplitude-modulated at similar EEG frequencies. Environmental electric fields (2.5-10 V/M at 7 c/see shorten subjective time estimates in monkeys and gradually increment hippocampal EEG activity around 7 c/see (Gavalas et al. 1970). Weak VHF radio fields (147 Me/see, 0.8 roW/era 2) amplitude-modulated at frequencies of EEG rhythm "signatures" in cat cortical and sub-

548 cortical structures increase occurrence of " s i g n a t u r e s ' a~ conditional responses and act as contingent reinforcers (Bawin et al. 1973). Intracerebral electric gradients so induced are many orders of magnitude less than postsynaptic gradients of 1 kV/cm. Increased efflux of *~Ca -~' and 3H-GABA follows electrical stimulation at t'-t:(i amplitudes (20.-50 mV/cm) that would produce only 2.5 /~V across a synaptic terminal (Kaczmarek and Adey 1974). There is a sharp "'tuning curve" for 4~(a~, efflux from isolated chick brain exposed to VHF fields (as above) only at modulation frequencies from 10 to 25 c/sec (Bawin et al. 1974). A hierarchical model of excitation is suggested. with initial cooperative binding and release of Ca as a longitudinal membrane interaction. Intrinsic EEG electric fields may relate to a "'second signaling s y s t e m " Supported by NSF Grant GB-27740 and U.S. Air Force Contract F44620-70-C-0017.

25. Mechanism of pathological slow waves.--(;. J. Ball and P. Gloor (Montreal, Queb., Canada). Single cell unit activity, surface and laminar EEGs were recorded from the suprasylvian gyrus of cats whose EEGs portrayed either generalized delta waves as a result of a mesencephalic reticular lesion or focal delta waves as a result of a white matter thermocoagulation lesion. Computer techniques of averaging the EEG showed that: ( 1) units were highly correlated with the positive phase o f a diphasic surface positive-negative average wave the duration of which depended upon the dominant frequency of the EEG; (2) units ceased to fire during the negative portion of the average delta wave: and (3) the slow waves showed phase inversion below a cortical depth of Itm. As unit activity correlated so highly with delta waves it was concluded that these are of neuronal origin, The dipole hypothesis applied to the laminar profiles of these slow waves suggested that pyramidal cells of the V cortical layer are the main generators of the delta waves. Thermocoagulation of the cortex or topical application of silver nitrate did not produce slow waves. Thus it was concluded that delta waves are a result of some form of deafferentation of the cortex~

26. EEG as an indicator of response to brain tumor chemotherapy.-& Spire, J. Renandin and A. S. Gevins (San Francisco and Los Angeles, Calif.). A longitudinal study of the EEGs ol28 patients with clinical and pathological evidence (open brain biopsy in most cases, post-mortem in some) of a brain tumor (glioblastoma in 25 cases, metastatic in 3) was performed in the attempt to determine the usefulness of the EEG correlation with the clinical response (neurological examination). The EEG, brain scan, and clinical examinations were compared every 6 weeks. The tests were all performed before a new course of steroids and chemotherapy was given. A total of 94 standardized EEGs was recorded leaving 66 EEGs for comparative purposes. These EEGs were all visually interpreted and arbitrarily classified (as for the brain scans) as better, worse or unehanoed on the basis of the extension/ amplitude of the slow wave patterns and/or the appearance

St)( 'IEIY PROCEEDIN(;S of cpilept~c activity. For some patients, the EEG evolution of the t u m o r was tracked using multi-channel auto-spectral and coherence analysis Fhe results, displayed on pseudothree-dimensional graphs of amplitude, frequency, and timc will be presented. Multiple step-wise regression analysis was applied to the computer-analyzed cases and will be discussed. In 65 % (43 of the 66 records), the EEG corresponded to the clinical observation. In 15 instances the EEG showed regression or progression, but the clinical examination was unchanged. However. in 6 of these instances the EEG was discriminative in indicating the trend of clinical evolution It would seem therefore that the EEG may be useful m determining brain tumor chemotherapy effectiveness.

27. The multiparameter numerographic somnogram.--K. Hanson, R, G. Bickford and M. Kalichman (La Jolla, Calif.). The utility of a compressed graphic display which combines spectral EEG with line length data representing electrooculogram and electromyogram has been demonstrated (San Diego Biomedical Symposium, t974). To provide wider clinical utility for this technique the following capabilities have been added: (1) Plotting of evoked potential contours at intervals in a column beside the spectrum. (2) Display o1 additional parameters, ECG (beat interval), respiration (breath interval) and body movement. (3) Providing numerical data on the above parameters outputted on a teletype with line spacing that corresponds in time to the graphic data. By joining the teletype and plotter strip charts a combined simultaneous spectral and numerical plot is obtained. The numerical plot data can be chosen to suit the particula~ clinical problem under review. (4) Simple algorithmb dependent on the numerical values generated can be developed to classify automatically such phenomena such as sleep stages. More importantly for clinical application, the numerical data can be used to develop criteria for separating active, passive, transient and waking stage activity in newborn and premature infants. In this study interaction indices indicating the degree of cardiopulmonary interaction during apnea are computed. These data have significance for studies of the sudden infant death syndrome. Supported by U.S.Public Health Service Grant NS 08962.

28. Determination of cionazepam effect on EEG by compressed spectral arrays (CSAs).--B. L. Ehrenberg, J. K. Penry, S. Sato and F. E. Dreifuss (Bethesda, Md. and CharIottesville, Va.). Clonazepam was administered to 8 children. 7 14 years of age, with recurrent absence (petit mal) seizures during a controlled double-blind study. Clonazepam doses ranged from 1.0 to 4.5 mg (0,023 0,093 mg/kg) daily. In 3 patients. absence seizures had failed to respond to a trial of ethosuximide. and phenobarbital was continued in 3 patients to prevent the recurrence of generalized toni~clonic seizures. Eight-channel referential and bipolar EEGs were taken before administration of clonazepam and after treatment for 4 days and again after 8 and 17 weeks. Each E E G was simultaneously recorded on magnetic tape and the CSAs (Bickford) were subsequently derived by a PDP- 12 minicomputer.

AMERICAN EEG SOCIETY Half of the children showed marked ( > 100 %) increases in activity at 14-24.9 c/see over pretreatment values, as measured by the average power spectral density or by the percentage of beta activity time (peak power histogram). These 4 patients all received clonazepam doses greater than 0.04 mg/kg. Theta activity (4-7.9 c/sec) was unchanged or diminished in all patients. These findings will be discussed in relation to the serum clonazepam levels as well as their persistence over the 17-week study period. Excessive beta activity was described in the routine EEG report of only 1 of the 4 patients who had an increase on CSA. 29. Time varying effects of diazepam and phenobarbital on spectral composition and rate of spiking in the spontaneom EEG of the limbic system and cortex in man.--J. P. Lieb, A. Siccardi, M. A. B. Brazier and P. H. Crandall (Los Angeles, Calif., and Genoa, Italy). Studies comparing the effects of diazepam and phenobarbital on the spontaneous EEG of the limbic system and cortex have been carried out in 11 patients with intractable temporal lobe epilepsy in whom electrodes had been implanted stereotactically and left in place for a period of 3-4 weeks for diagnostic purposes with a view to therapeutic surgery. Recordings were taken from several deep sites including the amygdala, hippocampus and hippocampal gyrus as well as from dural leads. Spectral arrays computed from 5 min time periods preceding, during, and following i.v. injection of the anticonvulsants indicated that: (1) while both drugs affected the cortex, diazepam (20 mg) had much more marked effects over a wider range of frequencies (especially in frontal cortex) than did phenobarbital (130 mg); (2) subcortically, only diazepam affected spontaneous activity; (3) drug effects were evident in the spectral arrays as early as 1 min following the start of injection. Visual and automated counts of spiking activity indicated that: (1) diazepam rapidly suppressed spiking during the course of injection in non-epileptogenic sites but tended to activate transiently spiking in epileptogenic sites; (2) i.v. phenobarbital produced only mild spike suppression; (3) following 3 and 6 days of p.o. diazepam (20-40 mg), there was a tendency for spike suppression only in non-epileptogenic sites. These data further indicate that only some proportion of the drug-produced changes in spectral activity can be attributed to changes in spiking activity. Supported by grants from Hoffmann la Roche and from NINDS (NS 11379). 30. A method of improving the estimation of spectra.--D. O. Walter (Los Angeles, Calif.). When short-epoch spectra are combined so as to yield an estimate of the "true" spectrum over a longer epoch, one usually averages the logarithms of the spectral intensities from the short-term spectra. Unexpectedly, the process of averaging may not give the most accurate available estimate of that "true" spectrum; for, just as the error variance in estimating an event related potential such as an evoked potential can often be reduced by Wiener filtering in the frequency domain (Walter, Marseilles Congress; Nogawa et al. ibid.), so also the error variance of an estimated long-

549 term spectrum can be reduced by Wiener "liftering", using what is nowadays sometimes called the "quefrency" domain. This error reduction procedure can be applied to many kinds of spectral estimation; the work which motivated it was the statistical comparisons of spectral intensities from symmetric placements over the hemispheres of patients, performed by Rosadini et al. (Conference on Computer EEG Analysis, Frankfurt, in press). They used a standard varianceratio or F test, which involved calculation of variances between repeated spectral estimates in a single channel, at each frequency. Wiener liftering should reduce those variances, and thus give a more definitive test of spectral differcncc~, 31. Combatting the eye motion artifact in spectral analysis.-D. R. Skuce, J. Gotman P. Gloor (Montreal, Queb., Canada). The problem of eye motion artifact is a serious one for spectral analysis in the frontal region, since the large delta component in the spectrum is hard to distinguish from true pathological slow waves. About 2 years experience has been accumulated using such spectra, and various means for dealing with eye motion have been investigated. The first consists in estimating the smoothness with which the delta spectrum falls off with increasing frequency, a characteristic of eye motion spectra not shared by pathological slow waves. The second method consists in recording on the computer the vertical and horizontal EOG along with the EEG. Various fractions of both components are subtracted from frontal channels before the analysis is performed, That fraction giving a minimum delta energy is then used during analysis to compensate partially each frontal channel. The third method was to experiment with various methods for holding the eyes, including plasticine, foam rubber and sand bags fitted to the eyes. The degree of improvement was assessed with spectral analysis. The use of at least the last two methods shows promise of reducing the artifact problem to acceptable levels during spectral analysis. 32. Heuristic algorithms for the analysis of sharp transient EEG waveforms.--A. S. Gevins, C, L. Yeager and S. L. Diamond (San Francisco, Calif.). While spectral analysis is useful for characterizing EEG background activity, it deemphasizes clinically important features including fast, sharp transient waveforms (spikes). The transient analysis algorithms to be discussed are incorporated in an mteractwe, real time spectral analysis and display minicomputer system. A moving average of the second derivative is used to isolate waveforms which are sharp with respect to the background activity. Candidate waveforms are then subjected to a sequential series of tests, modeling the methods of clinical EEG. If the sum of the weighted scores exceeds a preset, but variable threshold, a sharp transient event is reported. The test heuristics are: coincidence of sharp transients on adjacent electrodes; excessively low or high rate of

550 recurrence: surface-negative polarity for monopolar montages or location of phase reversals for bipolar montages: association with a wave of low curvature: and likeness to previously detected sharp transients. A patient's clinical history is used to set automatically moving average lengths. recurrence rate and surt:ace spread thresholds, as an aid in discarding artifacts. Feedback from the operator is used to adjust decision thresholds in real time to improve performance. Detection can be made to emulate individual clinicians by adjusting the weight given to each of the heuristic criteria in the final committee vote. Supported by U.S.Public Health Service Grant NS 10471.

33. The detection of surface EgG correlates of deep brain spiking in schizophrenic patients using matched digital filters.--B. Saltzberg and R. G. Heath (New Orleans. La.). in earlier studies on n o n - h u m a n primates (Saltzberg e t a / . 1971), it was discovered that a complex but consistent characteristic surface EEG wave shape occurred in synchrony with deep spikes recorded from implanted electrodes. This wave shape formed the basis for the design of a digital filter that was capable of detecting the presence of deep spiking from the monkey's surface EEG recordings alone. In our current studies we are evaluating the performance of a variety of digital filters. Their characteristics were estimated by analyzing the surface EEG of a patient whose deep recordings exhibited abnormal spiking activity. Using clues such as the transient wave shape of surface EEG activity when deep spikes are present, and the power spectrum of background activity, we are designing digital filters to study the effectiveness of detecting the incidence and amount of spikecorrelated surface EEG activity. Differences in the total n umber of such spike-correlated events are being studied as a basis for discriminating the EEGs of schizophrenics and normals. At the time of the writing of this abstract. 3 schizophrenic patients and 2 age-matched normal subjects have been evaluated using appropriate digital filter designs applied to 4 EEG channels. Our initial findings showed that spike-correlated activity in the schizophrenic patients produced 1.5 3 times as many surface spike-correlated events than were obtained from the normal controls.

34. Spatio-temporal characteristics of the 3/sec spike-andwave.--& R. Daube and B. F. Westmoreland (Rochester, Minn.). The potential fields of the scalp EEG during epileptiform discharges in 9 patients with petit mal seizures were studied using a technique of simulated, three-dimensional display. Filmed representations of the temporal fluctuations of the potential fields were obtained using a computer system which sampled 16 channels of EEG at 200 samples/see, generated an oscilloscope picture of each set of samples, and photographed them as sequential frames of 16 m m film. The waves and the spikes were found to be two spatially distinct activities. The wave was a regular, symmetrical, bisynchronous, initially positive fluctuation of voltage that arises in the posterior frontal region and shifts symmetrically anteriorly during its development. The spikes arise locally either on the midline or over one hemisphere as brief localized

s( ~('It fY PRO('EEDINGS reductions m positivit$. Iheir pattern of development i~ variable and they may shill either to the opposite hemisphere or anteriorly. However, in 2 patients the spike component of the spike-and-wave always originated at the site o f an inter-burst focal spike discharge Fhe spatio-temporal pattern of the 3 sec spike-and-~ a~ c suggests that its most important feature is the slow ,save component which terminates with a variable pattern of rapid fluctuations which are seen on the rouline t"EG as the spike component of the spike-and-wave.

35. Atypical EEG findings in subacute sclerosing paneneephalitis.--O. N. Markand and J. G. Panszi (Indianapolis, Ind.). EEG in subacute sclerosmg panencephalitis (SSPE) is xery often unique and almost pathognomonic (Radermecker 1949: Cobb and Hill 1950). In typical cases the EEG show:, stereotyped high voltage slow wave complexes which occur with a lair degree of periodicity throughout the tracing. usually occurring once every 4 15 sec. EEGs of 27 proven cases of SSPE seen in the last 8 year,,. were reviewed. In addition to the characteristic periodic complexes, the following atypical or less well known EF(; findings were seen: {11 I\~cal or asymmetric periodic coinplexes: (2) electrodecremental periods lk~llowing periodic complexes: (3) occurrence of rhylhmic delta activity between periodic complexes; (4) paroxysms of bilaterally synchronous spike-and-wave activity: (5) spikes, sharp waves or "'triphasic" waves over the frontal areas: and (6) focal abnormalities, such as spike or slo~ wave l\~ci Periodic events occnr in a wide variety of pathological processes and cases of SSPE may show several atypical findings, However, when the clinical context, results of measles antibody titers in serum and CSF and the charac teristic evolution of serial E EGs are taken into consideration. diagnosis of SSPE can be estahlished without brain biopsy

36. "Alpha'Mike EEG in coma after cardiac arrest.--S. Chokrover~ (Chicago, ill.). Apparently wakeful EE¢; pattern is known to occur in association with a comalose behavioral state m pontinc dysfllnction. Recently, a somewhat similar pattern, but with certain differences in topography and reactivity, has been described in comatose patients lk~llowing cardio-pulmonary l~.tilure (Sharbrough eta/. 1974). In 5 comatose patients EE(} demonstrated rhythmic, diffusely distributed, mostly nonreactive activities of alpha IYequency 24.96 h after cardiac arrest. Three patients died 2 5 days later. One palienl regained consciousness but expired after 2 months and the only survivor was left ~ith a mild dementia. EEG of one patient demonstrated spindle-hke activities in addition to the alpha-like rhythm while m another definite signs ol reactivity were observed. EE(is of ;3 patients with ventral pontine syndrome were contrasted with the above and both similarities and differences were noted. Recognition and further study of this EEG pattern in comatose patient~ following cardio-respiralory arrest is important from prognostic and pathogenetic points of view and, therefore, m till such patients daily recordmg of F,f!Gs should be performed for several days.

AMERICAN EEG SOCIETY 37. Alpha-pattern coma in high voltage electrical injury.-A. B. Grindal and C. Suter (Richmond, Va.). Two cases are reported in which reversible deep coma subsequent to high voltage electrical injury occurred in association with an alpha pattern in the EEG. This EEG pattern differs from the alpha rhythm of the normal waking patient by its diffuse distribution and its unresponsiveness to a variety of stimuli. The term "Alpha Pattern Coma" is introduced to designate the occurrence of this EEG pattern in the comatose patient. Similar EEGs have been reported previously in comatose patients. The literature on this subject is reviewed and shows that this type of EEG record has occurred primarily in association with irreversible brainstem lesions. The EEG in the present cases initially demonstrated activity of alpha frequency which occurred in a generalized distribution and was unresponsive to stimulation. During the early stages of recovery an increased incidence of theta and delta activity was observed. The recovery records contained a low voltage alpha rhythm which responded to photic stimulation. The possible modes of pathogenesis are discussed. The authors conclude that such examples of alphapattern coma might be detected more frequently in comatose patients who survive if these patients were studied earlier in their clinical course with EEG. 38. Pattern-sensitive epilepsy and spatial frequency channels in the human visual system .--M. J. Soso (Seattle, Wash.) Pattern-sensitive epilepsy (PSE) is a seizure disorder precipitated by visual patterns, particularly stripes. Investigations of human visual pattern perception (Graham and Nachmias 1971; Stromeyer and Julesz 1972) indicate the existence of sensory "channels" responsive to stripes. These channels are "tuned" to particular stripe widths (spatial frequencies) and are conjectured to participate in a Fourier-like analysis of the visual field by decomposing visual forms into elementary constituents (sinusoidal gratings). The role of these channels in PSE has been examined by Fourier analyzing patterns inducing EEG discharges in a pattern-sensitive patient (Chatrian et al. 1970). Epileptogenic patterns proved to have simple properties in the spatial frequency domain: (1) fundamental harmonics of 5-10 cycles/degree ; and (2) a critical phase and amplitude relation between the fundamental and the third harmonic. Since pattern epileptogenicity appeared dependent upon simple spatial frequency domain properties (narrow range of fundamental frequencies; phase and amplitude relations of harmonics) these results are considered consistent with a role for independent spatial frequency channels in the mechanisms of PSE. Supported by U.S. Public Health Service Grants NS 11563 and FR-37. 39. Photosensitivity in slow-wave sleep.--S. Sato, F. E. Dreifuss and J. K. Penry (Charlottesville, Va. and Bethesda, Md.). Following previous studies of the effects of sleep on spike-

551 and-waves in absence seizures, photosensitive discharges were studied in 4 patients, including identical twins, during various sleep stages. Sensitivity to stimuli at all frequencies and intensities was minimal during slow wave (Stages 3 and 4) sleep though photic driving was still discerned at times. Because of augmentation of visual evoked potentials in Papio papio using paired stimuli at 40 msec intervals (Naquet), trains of double stimuli were given. This mode was found effective in triggering polyspike responses during NREM sleep at 6-8 flashes/see with fash intervals of 40-60 msec. The morphology of the discharges was similar to that in spontaneous NREM sleep but the discharges were stimulus bound and did not lead to post-stimulation spike-and-waves frequently seen in the waking and REM sleep states. Increase in evoked potentials in photosensitivity has previously been shown. This is discussed in terms of comparison of the visual excitability cycle awake and asleep using paired flashes. The specificity of the stimulus modality is discussed in terms of the physiology of sleep. 40. Metamorphopsia--clinical and EEG study.--F. Morrell and D. Bergen (Chicago, III.). Two patients with unusual ictal alterations in visual perception were studied. In one patient convulsions began 16 months after surgical drainage of a left occipital abscess. Seizures were initiated by a perceptual illusion consisting of extreme vertical elongation of objects, especially lighted ones, e.9., light bulbs, mirrors, chandeliers, confined to the right visual field. Illusions were correlated with characteristic left occipital epileptiform discharges. Five years later the patient developed a second distinctive visual perceptual illusion, that of micropsia, clearly referred to the left visual field. The two illusions never occurred simultaneously but sometimes followed one another in rapid succession. EEG revealed independent right occipital epiteptiform activity temporally correlated with the illusion and suggesting that the latter was a consequence of secondary epileptogenesis. In contrast, a second patient presented with an aura of "dimming of vision" which initially gave rise to diagnostic confusion. Stereotaxic electrode exploration disclosed the initiating site to be the cingulate gyrus; stimulation reproduced the aura and also produced strong pupillary dilatation. In this instance the perceptual illusion was based entirely upon a peripheral mechanism rather than upon a disturbance in higher order visual integration. Such a possibility should be kept in mind in the interpretation of ictal visual symptomatology. 41. The concept of a seizure gating mechanism in epilepsy.-R. G. Bickford (La Jolla, Calif.). Evidence from multiple sources requires a third process intervening between input and output of the seizure mechanism. This "seizure gating system" (SGS) modulates the conversion of an EEG discharge into the varied components of a seizure. A disproportion between EEG discharge and seizure manifestation can be observed in: (1) identical twins

552

St )('IFTY PROCEEDIN(]S

where both members have spike-and-wave discharges but one only manifests an associated seizure: (2) matched spike-and-wave discharges from a patient which may, or may not, be associated with "'absence': (3) patients in whom successful anticonvulsant treatment is associated with an unchanged or deteriorated EEG recording (20-40!}, of patients under treatment); (4) patients undergoing successful treatment for seizures by cerebetlar stimulation via an implanted prosthesis (Cooper); (5) chloralose epileptic cat model in which the cortical discharge can be dissociated from the myoclonus by cerebellar stimulation (Myers). The existence of a gating mechanism is implied in c o m m o n terminology "'electrographic or larval" seizures. Great care is needed in the use of the term "'seizure discharge" in both animal and" h u m a n situations, otherwise serious confusion results. The anatomic substrate for inhibitory functions subsumed under the "'SGS'" can be conjectured as existing at multiple neuraxis levels (subcortex. caudate, cerebellum. ,-eticular system and spinal cord). Supported by U. S. Public Health Service Grant NS 08962. 42. The EEG in Menke's syndrome.--R. Lewis and P. Moe (Denver, Colo.).

Leshner, J. A.

Menke's kinky hair syndrome is a multi-system degenerative disorder associated with very low levels of blood copper and copper oxidase. Inheritance follows a sex-linked recessive pattern. Protkmnd central nervous system involvement is seen, characterized clinically by hypotonia, psychomotor retardation, seizures, and focal neurologic findings. CNS changes are probably due to abnormalities in cerebral blood vessels and impairment of mitochondrial cytochrome oxidative system. Serial EEGs on an infant male with this syndrome beginning at 4 m o n t h s showed an initial pattern of focal and generalized spikes and spike-and-waves occurring against a slow background. These gradually progressed to electrical status epilepticus with frequent clinical seizures, despite parenteral copper therapy. The nature of the EEG abnormalities probably reflects the underlying widespread, multifocal degeneration of cortex and white matter. The EEG may provide useful information in Menke's syndrome. By the time the full-blown E E G pattern has evolved, however, severe and irreversible brain damage has occurred. A literature review of the clinical, biochemical and EEG findings and the experimental treatment of this disease with parenteral copper, will be presented, 43. The EEG during monitoring and control of intracranial pressure in Reye's syndrome.--R. P. Tucker, G. W. Kindt, J. Waldman, C. Kohl and J. Baublis (Ann Arbor, Mich.). Aoki and I.ombroso established the EEG as an important prognostic aid in Reye's syndrome. They classified EEGs into six groups. EEGs which fell into their grade 3 had about 50",, chance of survival. Only one patient who had on admission a grade 4 E EG or worse survived in a vegetative state. During the recent influenza epidemic, 13 patients with Reye's syndrome have been treated in this hospital since February of 1974. Of the first 10 patients, none with a grade 4 EEG or worse survived despite peritoneal dialysis, exchange transfusions and vigorous anti-edema therapy. There were 5

deaths in this group of 10 The last 3 patients had subdural pressure lnonitoring ill addition to other therapy, l w o of these patients survived. including one whose initial 3 I!EGs ~ere grade 4. Both had minimal neurologic deficits. All 3 had positive spikes in their EEGs during coma. a pattern not noted in the EE(is o[ the 2 survivors on recovery. EEGs were monitored throughout the course of their treatment. It is felt that continuous monitoring of mtracranial pressure may be important in the management of Reye's syndrome. 44. EEG aspects of different methods of obstetrical delivery in newborn infants.--C. Cristian and R. April (Roosevelt Island, N. Y.). Some methods of delivery 'a~c potentially more traumatic lo the infant cranium than others. Therefore, 66 normal, fulb term inl:ants delivered b~ different rnethods (Caesarian. forceps, vacuum extraction, and spontaneous) were studied electroencephalographically between 10 and 40 m m after birth to look for significant correlations. We will describe a specially constructed set of 8 lead-tin electrodes held in place by special bands, designed to minimize pressure on the cranium. Follow-up tracings were made on 20 of the infants at intervals up to 1 years of age. During the initial and follow-up periods clinical observations of psychological and physical development were normal Non-parametric statistical analysis of the data failed t~, reveal a significant difference from random distribution between 5 graded categories of EE(i frequency patterns and either the method of delivery or the age of the parents Floweret, analysis of broader categories of EEG frequency patterns (slowest rs. l:aslest) in those delivered by Caesarian rs. forceps methods was significant at P < 0 . 0 5 . Faster frequencies were seen after Caesarian: slower, alter forceps deliveries. Similarly. analysis of these broader EEG categories showed a significant difference (P<0.0005) between mean ages of parents of newborns will) faster and slower I:FG palterns 45. Clinical correlations with EEGs recorded 20 years after head injury.--R. R. Young and W. H. Timberlake (Boston, Mass.). I'ilis study deals with EEGs recorded h-om 200 U.S. veterans who were examined 16 22 years after injury in the Korean War. The injury involved the head in 159 but was restricted to other parts of the body in 41 controls. From the control group, 37;41 records are normal. 2 borderline and 2 abnormal In tile head injured group, normalization of the EEG had occurred in most instances despite I he persistence of neurological disability. The records are now either: (I) normal {64,159); (2) borderline (34) because of minor asymmetric,, oF normal activity a n d o r infrequent low voltage thela activity (which appears significant only upon correlation with the site of injury): or (3) abnormal {61 ). Even in this last group, the localized irregular slow activity was usually of lms amplitude 10 30HV in 33 and 30 5 0 H V i n 1 0 . 1 n 1 0 p a t i e n k however, higher amplitude irregular non-paroxysmal slox~ activity persisted at the site of injury and was associated with

AMERICAN EEG SOCIETY clinical seizures in 9 cases. On the other hand, seizures were present in only 3 of 8 patients whose records contained spike or sharp wave activity. In our material, the presence at the site of the original lesion, 20 years after injury, of non-paroxysmal irregular slow activity greater than 50 #V in amplitude is highly correlated with seizures. Several other EEG~zlinical correlations will be discussed. Supported by the J. A. Hartford Foundation, Inc.

46. EEG characteristics of solitary intracranial lesions in relationship to anatomic location.--R. S. Rhee, E. S. Goldensohn and R. C. Kim (New York, N. Y.). Twenty-six solitary discrete lesions, predominantly neoplastic, from 756 consecutive brain autopsies and 9 of 100 consecutive surgically excised convexity meningiomas were studied, in an attempt to develop a correlation with EEG findings. In the autopsy material, distances between the nearest margin of each lesion and the cortical positions underlying each electrode were measured according to Jasper's schema for the relationship between scalp electrode placement and underlying cortex. The lesions were divided into 6 groups according to the sites of anatomic involvement : (1) cortex (meningiomas); (2) white matter; (3) cortex and white matter; (4) subeortical gray matter and adjacent white matter; (5) cortex, white matter and subcortical gray matter; (6) brainstem. The EEG characteristics of each group will be presented. A m o n g the features to be discussed will be the high incidence of polymorphic arrhythmic delta activity associated with lesions predominantly involving white matter, the high incidence of irritative features associated with lesions exclusively involving white matter, and the relatively greater incidence of unilateral or bilateral supplantation of alpha r h y t h m by slower waves in association with vascular lesions as opposed to neoplasms. Some aspects of effects upon the EEG of lesion size will also be discussed.

47. The use of succinylcholine in the determination of electrocerebral silenee.~C. Suter (Richmond, Va.). A review of over 600 EEG recordings done in the course of a study of c o m a and cerebral death showed that muscle artifact was the most difficult problem encountered in determination of electrocerebral silence. During the first part of the study when :succinylcholine was used rarely nearly 10% of the records were considered unsatisfactory for determination of electrocerebral silence usually because of muscle artifact. Often this was due to "'low amplitude fast activity". During the latter part of the study succinylcholine was used frequently and the n u m b e r of records unsuitable for determination o f electrocerebral silence was reduced to I or 2%, Also the "low amplitude fast activity" nearly always turned out to be muscle artifact abolished by use of succinylcholine. The dangers and possible adverse effects of succinylcholine and other muscle relaxants are reviewed and proper precautions for their use outlined. A case of cardiac standstill during the rapid injection of succinylcholine is reported. Nevertheless, it is concluded that succinylcholine used properly is the most useful agent for elimination of muscle

553 artifact and in m a n y cases essential to determination as to whether a record shows EEG activity or electrocerebral silence.

48. Pseudoperiodic lateralized epileptiform discharges (PLEDs) in chronic neurological patients.--R. April and C. Cristian (Roosevelt Island, N.Y.). Five patients are reported with P L E D s in repeated E E G recordings 8-36 m o n t h s after an acute cerebral insult. P L E D s are described in detail -amplitude, duration, localization, background activity, relation to state of consciousness and provocation procedures. Some tracings included recording from nasopharyngeal electrodes. Clinical-anatomical correlation is presented. Our observations reveal certain important differences from those made by other workers (Chatrian et al. 1964, 1964; M a r k a n d and Daly 1971 ; Schwartz et al. 1973), who emphasized the rapid evolution of PLEDs with focal clinical seizures. These features were not seen in our patients. Possible mechanisms for PLEDs are discussed. Finally, it is hypothesized that the exclusively unilateral representation of P L E D s might be one sign of disconnection from the contralateral cortex. Because severe, unimproved aphasia was seen in 4 of our patients, the possible functional significance of the above hypothesis is discussed from the following points of view: first, in theoretical terms of recovery of function in aphasia; second, in relation to the observation that in one of our patients administration of diphenylhydantoin was associated with disappearance of P L E D s and improvement in general behavior, but no improvement in language function.

49. Status epUepticus.--G. G. Celesia

(Madison, Wisc.).

Status epilepticus occurred in 52 of 1,835 patients representing a prevalence of 2.8 %. Its relative frequency increased in adult life. Status epilepticus is defined as a seizure lasting at least l h or one repeated often enough to produce a fixed enduring epileptic state o f at least I h duration. Various forms of status epilepticus were observed: the most frequent was grand mal status either generalized from the beginning or with focal onset and secondary generalization. Next in frequency was focal status epilepticus. Absence status manifested as a twilight or stuporous status was seen in 4 patients. One patient had psychomotor status. Status epilepticus is often symptomatic of a massive destructive process in the central nervous system. Despite modern treatment status epilepticus still remains a dangerous condition having a high mortality rate. EEGs during and following status epilepticus are most useful in distinguishing between idiopathic and symptomatic status epilepticus. A persistent slow EEG focus is most often indicative of a destructive brain lesion. The EEG is indispensable in the diagnosis of absence and psychomotor status.

50. Clinical correlations with children's EEG showing unusually slow barbiturate-induced beta activity.--J. A. Zeese and F. Torres (Minneapolis, Minn.).

5.54 Sleep EEGs on children sedated with Seconal usuall} shm~ prominent beta activity in the 20 25 c/sec range During a period of one year approximately 110 E EGs were taken from children sedated with Seconal. Ten of these records were ,Iriking because they showed prominent beta activit 3 with a lower frequency than the rest (14 20 c:sec). Physical examL nations on all showed evidence of significanl dill'use, severe brain dysfunction of a congenital or degenerative type. often ~ith microcephaly or chromosomal abnormalities. The clinical status of these children will be compared with those showing beta activity from Seconal in the usual range, and diagnostic and prognostic possibilities of the pattern ~q" slower frequency drug effect will be discussed. 51. Activation of focal delta abnormality with methohexital and other anesthetic agents.---P. L. Hansotia, F. ~ . Sharbrough and J. Berendes (Marshfield, Wisc. and Rochester, Minn.). Previous studies have demonstrated the value of sodium methohexital (Brevital)-induced narcosis for activation of both focal and generalized epileptiform discharges This report will deal with a less known phenomenon of activation of both l\mal and delta abnormality, both ~ith Brevital and other anesthetic agents. 350 cases were studied with Brevital narcosis at Marshrield. Wisconsin. 22 patients showed l\~,cal deha slowing during induction of anesthesia and all showed recovery from lh e focal delta abnormality on awaken ing from t he procedure. Of these, one had an astrocytoma while most others showed atrophic lesions 200 cases undergoing carotid endarterectomy at Rochester, Minnesota. were studied with EEGs during induction ~ ith Pentothal and during maintenance with Halothane and nitrous oxide 15 of these cases, who were free of significant focal abnormality during their waking trace, showed a persistent delta focus throughout induction and maintenance of anesthesia. This delta focus disappeared at the termination of the procedure. The delta focus was on the side of a previous ixchernic attack, although, al the time of the procedure, only 6 cases had a residual neurological deficit. In conclusion, we feel that activation oflk)cal delta abnormality dnring anesthesia is an additional advantage to using Brevital as an activating technique. $2. Positive occipital sharp transients of sleep: relationships to nocturnal sleep cycle in man. V. Vignaendra, R. L. Matthews and G. E. Chatrian (Seattle, Wash.). Positive occipital sharp transients of sleep (POSTS) are detected over the occipital regions of some healthy human sul2jects (Gibbs and Gibbs 1952}. Striking similarities in ~aveform. polarity and topography exist between these potentials (POSTS) and the lambda waves (LWs) occurring in ~saking subjects intent at visually exploring an illuminated patterned field Overnight polygraphic recordings were perlormed on (~ ~ubjects who had no significant findings on neurological examination and normal diurnal waking and sleep EEGs. POSTS were numerous during N R E M sleep and occurred more frequentl?, during Stages 2 and 3 than 1 and 4: howexer.

S( )( t e l Y PROCEEI,HN(;-S Ihex were absent ,)r vcrx rare during REM sleep, lhcsc findings suggest that P()STS arc most unlikely to be related to oculomotor activil; and nr visual dream imagery. Wc propose that these events ma~ indicate some form of inl'o~ • marion "'playback" occurring during N R E M sleep in cortical visual areas. The purpose ~1"this postulated playback might be to re-examine lhe vast amount of visual material collected during the day perhaps sorling analyzing and compressing novel, relevanl dam ik~r longqerm memor> storage while simultaneously reieeting redundant a n d o ~ irrelevant information. ,~3. rhe EEG in patients with vertebrobasilar insufficienc~ and dementia.--V. M. Rivera (Houston, Texas). Vertebrobasilar [nsufficienc~ i V BI )is the most c o m m o n form of chronic arteriosclerotic cerebrovascular disease. Dementia with predominant memory deficits can be developed as a resuh of chronic and episodic ischemia in the areas irrigated by the posterior circulation, namely the medial portion of the temporal lobes, limbic system, mammillary bodies, parietal and occipital cortices l!FiGs of I10 patients ailh VBI and dementia uere reviewed. Selection of these patients was done prospectively with stric! clinical and angiographic criteria m order to achieve the study of cases with symptoms, neurological deficits and dementia basically attributable to VB[. Presence of dementia in every patient was confirmed and graded using a battery of nine psychological tests Most of these patients had EE(}s with normal characteristics although bitemporal slowing was not u n c o m m o n and unilateral focal abnormalities associated with abnormally s l o w background rhyfilm aere also fl)und A predominant pattern was not identified. local abnormalities did not correlate with neurological findings and they probably represented associated hemispheric lesions in the carotid-anterior or middle cerebral ~rteries distributions Fhere a a s no l E G correlation with severity of dementia and neurnlogical deflcfls 54. Receptors in focal reflex myoclonus.---(L (L Sutton ,Jr. (Baltimore, Md.). Marsden el al. (1973) seek to extend the traditional view ol the muscle stretch reflex to include a transcortical pathwa', and imply that muscle stretch is the essential stimulus for the jerks in certain patients with myoclonus epilepsy In a patient with focal reflex myoclonus, a large somatosensory evoked response (SER) and a long loop C reflex recorded from finger flexor muscles could be evoked bv stimulation of the right median nerve, at the wrist or digits. Moreover. exlension of the index finger and electrical stimulation of the middle finger of the right hand were alternately performed while recording the SER and C reflex. I'o eliminate the contribution of muscle afferents ot the flexm digitorum sublimis and profundus, an infant blood pressure cuff was inflated at the wrist to produce pressure block of nerves to the right hand I'his produced gradual attenuation and eventual disappearance ~f the SER and C reflex to Ix3lh electrical stimulation and extension of the fingers Therefore. muscle stretch does not significantly contribute to the SFR and long Ic,op C reflex

AMERICAN EEG SOCIETY The relative contribution of touch or pressure, and joint receptors to the SER and C reflex was also assessed. 55. Correlation of the aura and behavioral sequence with the electrical activity recorded by depth electrodes from the hippocampus of patients with seizure disorders.---G. O. Walsh (Los Angeles, Calif.). In patients with medically refractory seizure disorders electrodes are implanted in appropriate areas of the depths of the brain to determine if there is a single focus from which the patients" seizures arise. In patients with temporal lobe seizures a correlation was made between the build up of rapid spike discharges signifying the start of the clinical seizure and the patients' aura. It was found that if the seizure discharge was confined to one area o f the hippocampus, the patient did not have an aura. If the discharge spread to other areas on the ipsilateral side, the patient experienced the aura. When the discharge spread bilaterally, the patient manifested the actual psychomotor seizure. Simultaneous recording of the patient's clinical seizure and the EEGs recorded from both surface and depth will be illustrated by film or video tape. Supported by a grant to Dr. P. H. Crandall from NINDS.

555 hallmarks of microelectrode recordings from single neurons in epileptic foci of both humans and animal models. The relationship between these bursts and the EEG interictal spike, recorded locally by the microelectrode, or from surface o f overlying cortex has been examined in recordings from human epileptic loci. Relationships were also sought between interictal bursts from nearby cells when action potentials from several neurons had been simultaneously recorded by the tungsten microelectrodes. The degree of synchrony between interictal bursts from adjacent cells, and between bursts and either the local or cortical EEG spike varied greatly in epileptic loci of different patients. In the majority of patients synchrony has been uncommon; interictal bursts do not occur in any fixed relations.hip to the local or cortical EEG spike. But in a few patients a high degree of synchrony between bursts and local EEG spikes has been recorded. Foci in these patients demonstrated unusually frequent spontaneous seizures. Synchrony between bursts may be important in the transition from interictal to ictal events in man; synchrony between bursts and local EEG spikes may also be involved in this transition.

56. Thresholds for after-discharge and evoked potentials in patients with temporal lobe epilepsy.--D. G. Cherlow, A. M. Dymond, E. A. Serafetinides, R. D. Walter and P. H. Crandall (Los Angeles, Calif.).

58. Metabolic and electrophysiologic mechanisms in the initiation and termination of enflurane-induced seizures in man and cats.--K. J. Burchiel, J. J. Stnekard, R. R. Myers, N. T. Smith, R. K. Calverly and R. G. Bickford (La Jolla, Calif.).

Depth electrodes have been implanted into the brain of patients with medically uncontrolled temporal lobe epilepsy in order to determine their suitability for surgical treatment. As part of the diagnostic procedure, each of these electrodes is stimulated electrically. The records of the stimulation sessions for 30 patients were examined for threshold levels of evoked potential and after-discharge production. Comparisons were made between anatomical sites, the resected r e r s u s non-resected temporal lobes, and types of pathology found in the resected specimen. Patients with hippocampal sclerosis had higher thresholds in structures on the resected side, and an explanation of this using a deafferented model of epileptic tissue is proffered. The patients without hippocampal sclerosis differed in that they showed no differences in evoked potentials or afterdischarge thresholds between the resected and non-resected side. Also, on the non-resected side of patients with hippocampal sclerosis, the hippocampus had a higher threshold for after-discharge production than did the hippocampal gyrus. This was not the case for patients with sclerotic pathology, a fact suggestive of bilateral damage in this group. Additionally, for all patients, the amygdala had a much higher threshold for after-discharge production than either the hippocampus or hippocampal gyrus. Supported by a grant to Dr. P. H. Crandall from NINDS.

In a study of the neurophysiologic and metabolic effects of deep enflurane anesthesia in 10 healthy volunteer patients, grand mal seizure patterns were precipitated by auditory, visual, or tactile stimulation at brain-equilibrated end-tidal concentrations of 3-6 ~/o. The minimum epileptogenic concentration was approximately 1 °/~ lower (than that at normocarbia) when the PaCO2 was 20 mm Hg, and 1°~, higher when PaCO2 was 60 mm Hg. These findings were reproduced in cats and with depth recording it was seen that the seizure activity originated in the amygdala and spread rapidly to neocortex. Administration of scopolamine increased the incidence of spontaneous seizures at epileptogenic concentrations of enflurane, as well as the manifestations of myoclonus and tonic~lonic movements during the electrographic seizures; this effect was reversible with physostigmine. Fast sinusoidal activity (20-55 c/sec) originating in the limbic system and propagating predominantly to VL of thalamus and neocortex was consistently associated with termination of the electrographic and clinical seizures. The effects of enflurane seizures on cerebral arteriovenous oxygen difference in humans and the experimental animals will be discussed as will the results of 16-channel ECoGs to determine the origin of the enflurane spike-andwaves.

57. Human epileptic foci--search for synehrony between bursting activity of single neurons and local and surface EEG spikes.---G. A. Ojemann, W. H. Calvin and A. A. Ward Jr. (Seattle, Wash.).

59. Effects of aminophylline on the EEG and seizure thresholds of the rat.--J. Walker, R. Friedman, P. Goodman and E. Lewin (Denver, Colo.).

High frequency bursts of action potentials are the interictal

Intravenous aminophylline is commonly used for the treatment of acute asthmatic attacks. Unfortunately, convulsions

556 occasionally occur following its use (Lancet. 1973). Accordingly, we have looked at the effects of aminophylline on the EEG and electroshock and pentylenetetrazol seizure thresholds ol the rat. Aminophylline given by tail vein infusion produced severe tonic convulsions and death at an average dose of 3 6 9 + 6 6 mg,kg. Equivalent doses given intraperitonealty were associated with the gradual development of low-voltage fast activity, followed by repetitive spike activity, convulsions, and death 2 ~, h later. When given intraperitoneally in a non-convulsi~ e dose ( 150 mg/kg) there is a significant lowermg of electroshock and pentylenetetrazol seizure thresholds. which is maximal about 20 min after the injection of aminophylline. Previous work in our laboratory has shown that aminophylline applied directly to ral cortex is epileptogenic. a s are other agents which increase cortical cyclic A M P This study supports the clinical suspicion that aminophylline is capable of producing seizures in susceptible individuals. Studies are in progress, using the rat model, to determine \~hich anticonvulsants are most effective in blocking aminophylline seizures

>;tR'IETY PROCEEDINGS 60. Peripheral and central input to postcentral cortex cells during active movements.--M. J. Soso and E. E. Fetz (Seattle, Wash.). Parietal EEG potentials preceding a c m c movement (l)eeckc e t a / , 1969) suggest that postcentral "'~ensory'" cortex cells may discharge prior Io active movement. In 7 rhesus monkeys. we recorded postcentral unit activity and biceps atld triceps E M G activity during active flexion and extension of the contralateral elbow a ilh the forearm in a hinged cast. Responses of 67 cells were averaged over 70 cycles ol flexion and extension. Sixty units laud receptive fields on lhe contralateral arm (24 with cmaneous fields and 36 responsive to deep tissue stim u l a t i o n ) 7 were not classifiable. One-third of the cells began firing I00 msec or more betbre agonisl F M G activity (mean onsel latenc~ of all units: 32 msec belk~rc biceps E M G and 77 msec bel;~re h-iceps E M G : range: 340 msec before to 280 msec afler agonist EMG onsetl. Early discharge was observed m all types of units independent of modalfly or receptixe field location. E M G activity ol nonagonisl muscles (hand. shoulder, axial) usually fc,llowed but never preceded by more ihan 60 msec the agonisl EM(; activily Thus. activity of postcentral cells preceding peri pheral discharge suggesls a central mptn 1o these cells during lctive movernenls. Supported by I..S.l'~ublic Heaflh Service Grants RR 0016¢, ~md NS 11027