American encephalographic society: 32nd annual meeting

Electroencephalography and Clinical Neurophysiology, 1980, 49: 1P--15P

1P

© E l s e v i e r / N o r t h - H o l l a n d Scientific Publishers, Ltd.

Society Proceedings AMERICAN ENCEPHALOGRAPHIC SOCIETY: 32nd ANNUAL MEETING San Francisco, S e p t e m b e r 4--9, 1978

Programme Director: Dr. J. E N G E L Room 1250, Reed Neurological Research Center, University of California, Los Angeles, Calif. 90024 (U.S.A.)

1. The a m b u l a t o r y cassette recorder: its role in the EEG work-up o f patients with focal epilepsy. -J.R. Ives and J.F. Woods (Montreal, Canada) In an earlier publication, the cassette had been r e c o m m e n d e d for use with p r o b l e m s associated with generalized epilepsy or differential diagnosis. However, w h e n used with c o m p l e t e appreciation of its i n h e r e n t limitations and then only as an adjunct to the E E G work-up of epileptic patients (prolonged sleep, sphenoidal recordings and cable-telemetry seizure m o n i t o r i n g ) the cassette can provide i n f o r m a t i o n relevant to the diagnosis of focal epilepsy which is n o t otherwise available. In a group of 50 focal epileptic patients, only 18% had their seizures d o c u m e n t e d by extensive conventional E E G procedures. 32 o f these patients were also investigated by cable-telemetry seizure m o n i t o r i n g system so that n o w 40% of the patients had their seizures fully recorded. H o w e v e r , by m o n i t o r i n g this group of 50 patients with the cassette f r o m 1 to 9 days, 80% had their s p o n t a n e o u s seizure recorded. The role of the 4-channel cassette as an adjunct to c o n v e n t i o n a l and cable-telemetry E E G as well as comparison b e t w e e n seizures r e c o r d e d by the 3 different media will be s h o w n and discussed.

2. Quantitative m e a s u r e m e n t s o f e p i l e p t i c spike morp h o l o g y in t h e h u m a n surface EEG. - - J. G o t m a n and P. G l o o r (Montreal, Canada)

A previously d e v e l o p e d m e t h o d of a u t o m a t i c recognition and q u a n t i f i c a t i o n of interictal epileptic activity was used to measure m o r p h o l o g i c a l characteristics o f spikes or sharp waves (SSWs). Each SSW was divided into first and second half-wave. T h e amplitude, duration, and slope near the apex, were measured for each half-wave; values were averaged over all SSWs of a channel. Statistical comparisons determ i n e d the m o r p h o l o g i c a l a s y m m e t r y of SSWs for that channel, with respect to the three measures. 150 bipolar channels f r o m 28 patients were analyzed (a

channel was analyzed w h e n at least 10 SSWs were detected). In m o s t channels we f o u n d the e x p e c t e d asymmetry in a m p l i t u d e (85%) and duration (73%), the seco n d half-wave being significantly larger and longer than the first. The reverse was never f o u n d (remaining cases s h o w e d no significant a s y m m e t r y ) . Slope asymm e t r y was significant in 30% o f channels. S o m e w h a t u n e x p e c t e d l y , the second slope was the highest in 80% of these cases. This was c o n f i r m e d by close e x a m i n a t i o n of the EEG. In 13 recordings showing SSWs in b o t h hemispheres but a lateralized main epileptic focus, slope a s y m m e t r y was significantly m o r e f r e q u e n t on the side of the focus (37%) than on the contralateral side (17%). No such difference existed for a m p l i t u d e and duration.

3. The clinical correlates o f m u l t i p l e spike loci. - Jean M.B. Moure and P. K e l l a w a y ( H o u s t o n , Texas) Three h u n d r e d and seventy-four children with multiple spike loci, aged 2 m o n t h s to 16 years, have been studied. Seizures were present in 79% of the patients. O f these, 45.9% had generalized tonic-clonic and 34.6% had simple, partial seizures. Mental retardation was evident in 43.6% of all cases. F o r t y perc e n t of the retarded patients and 81% o f the nonr e t a r d e d patients had o n s e t of their seizures in the first year of life. F o r t y - n i n e of the patients had seizures which were hard to control. The m u l t i p l e spike foci were first r e c o r d e d b e t w e e n the ages of f o u r and eight years in 64% of the patients. Longitudinal studies showed a trend for b o t h the m u l t i p l e spike foci and the seizures to disappear with time. In a small group of cases, seizures persisted for m a n y years. E E G s p e r f o r m e d on 129 patients prior to the demonstration of the m u l t i p l e spike foci s h o w e d single spike foci in 54.3% of the cases and h y p s a r r h y t h m i a in 6.9%. 14.4% of the 374 patients did n o t have seizures

2P and were not retarded. The majority of these had been referred for EEGs because of learning and/or behavior problems. Identification of etiological factors responsible f o r production of multiple spike foci could not be made in 48% of cases.and in the other 52%, the evidence was often circumstantial.

4. Blood induced e p i l e p t o g e n e s i s : e f f e c t s o f various blood components. -- E. Hammond, R.E. Ramsay, H. Villareal and B.J. Wilder (Gainesville, Fla.) A model for post-traumatic epilepsy was previously proposed in which 25 pl of homologous blood was injected into the cortex of cats. A very active spike discharge developed after 6 months. The present experiment was carried out to substantiate and extend these findings. Whole blood, packed RBC, ferric chloride, ferrous chloride, methemoglobin, ferratin, fibrinogen, hemin, water, cottonoid, or platinum was injected or inserted into the parietal cortex of guinea pigs (seven animals in each group). One group underwent sham operation. Histology was obtained on each group at 3--5 months and 7--8 months after lesioning. All but the sham group initially showed intermittent slow waves focal to the area of the lesion. After 2--3 months, the EEG in the water, platinum, and co t to n o id groups returned to normal, while in the other groups, the slow wave activity became higher voltage and occurred in short runs with sharp waves and occasional spikes admixed; all recorded from the area of the lesion. No difference was found between the groups in the time of onset or in the morphology of the discharges. In this study, the epileptogenic response was related to the tissue reaction elicited and does not specifically support the previous hypothesis that iron was the epileptogenic component.

5. Analysis of asynchronous neuronal interactions in acute epileptogenic foci produced by topical penicillin in r a t St c o r t e x . - - R . N . H a r n e r and O.M. Sgro (Philadelphia, Pa.) Single unit recordings have documented high frequency bursts in extracellular recording and intense depolarization in intracellular recording from neurons in experimental epileptogenic foci. A general tendency toward 'synchronization' in the population of epileptogenic neurons has been inferred from the temporal relationship of such findings to the inter-ictal spike recorded from the overlying cortical surface. The present study provides information concerning interaction between extracellular units detected with a linear array of 4 insulated tungsten microelectrodes,

SOCIETY PROCEEDINGS spaced at 100 pro, during pentobarbital anesthesia, before and after topical penicillin. High resolution (1 msec/12 ram) polygraphic replay from FM taperecorded data and latency histograms computed by a PDP-8E showed few interactions between adjacent units before penicillin. Afterwards, one-way connections appeared between units 100--300 ~tm apart with latencies of 0.5--5.5 msec. There were no synchronous units. The present findings suggest the importance of long-loop and/or polysynaptic connections between nearby neurons in the penicillin focus. Extension of this model will provide further insights into the circuitry of normal and epileptogenic 'synchronization' in the cortex.

6. Identification of epileptogenic loci during e n f l u r a n e a n e s t h e s i a . - - R.R. Myers and H.M. Shapiro (La Jolla, Calif.) Electrocorticographic (ECoG) and depth recordings have previously demonstrated the epileptogenic nature of surgical concentrations of the volatile anesthetic enflurane. We contrasted EEG activity-with local cerebral glucose uptake ([14C]2-deoxyglucose autoradiography) in 23 brain structures in order to identify the epileptogenic foci. Autoradiograms were obtained from sectioned rat brain following a 30-rain period of steady-state anesthesia at 1, 1.5, or 2 MAC enflurane. Pseudo-epileptiform ECoGs were obtained at 1 MAC. At 1.5 MAC, the ECoG displayed frank epileptiform activity with large amplitude spike-wave complexes; repetitive auditory stimulation occasionally precipitated grandmal seizures. At 2 MAC, spikes were less frequent and could not be repetitively driven. At 1 MAC enflurane, regional cerebral metabolism was depressed approximately 30% from the awake controls. However, metabolism in the dentate gyrus and other subcortical structures in the limbic brain was increased. At 1.5 MAC we observed increased metabolism in the hippocampus, habenula, habenulointerpeduncular tract and interpeduncular nucleus and a lack of significant decrease in entorhinal cortex, medial thalamus, hypothalamus and pineal. Metabolism in all other structures was significantly depressed (P < 0.05) compared to awake values. At 2 MAC, metabolism was decreased in all structures. We conclude that the low-seizure threshold hippocampus and related structures associated with the limbic system and its pathways are the epileptogenic foci for seizures induced with enflurane in the rat.

Supported by the Veteran's Administration.

AMERICAN EEG SOCIETY 7. Effects of cooling and lesions of the inferior thalamic peduncle (ITP) on spindles, recruiting responses and the epileptic discharges of generalized penicillin epilepsy in the cat. -- P. Gloor and A. Pellegrini (Montreal, Canada) Earlier experiments had demonstrated a close relationship between spindles appearing in the EEG of normal cats and the epileptic bursts in cats having received a large intramuscular dose of penicillin. It has been postulated that the ITP is the main thalamic outflow of thalamocortical volleys inducing spindles and recruiting responses. Inactivation of this pathway by cooling or its actual destruction by a lesion should thus abolish spindles and recruiting responses in the normal cat, and epileptic bursts in the penicillinized cat. Cooling the ITP actually produced these expected effects. However, actual destruction of the ITP did not abolish spindles or recruiting responses in normal cats, nor did it eliminate the epileptic bursts in penicillinized cats. It was hypothesized that cooling eliminated spindles and epileptic bursts through indirect activation of the desynchronizing midbrain reticular system, probably through the release of preoptically mediated inhibition of that system by concomitant cooling of the preoptic thermoregulatory area in the vicinity of the ITP. This hypothesis was supported by the observation that neither spindles, nor epileptic bursts could be abolished by ITP cooling after a bilateral lesion in the midbrain reticular formation had been made.

8. Changes in sleep EEG spectral densities with seizure reduction following EEG feedback training in poorly controlled epileptics. -- M.B. Sterman and M.N. Shouse (Los Angeles, Calif.) This study examined the sleep EEG effects of EEG feedback training in a group of 8 poorly controlled seizure patients. After baseline polygraphic sleep recordings, patients were initiated on a double or triple crossover design. Training was based on the simultaneous detection of two central cortical (C3--T3) EEG frequency bands (6--9 Hz and either 12--15 or 18--23 Hz), with reward provided for the occurrence of trains of one in the absence of the other. The design consisted of successive 3 m o n t h periods of training, with reward contingencies reversed after each. All-night sleep EEG recordings were obtained prior to each reversal. Three 10 minute samples of stage 2 sleep EEG data were subjected to an analysis which quantified spectral density in sequential 3 Hz bands from 0 to 19 Hz. Significant seizure reductions were registered by 7 of the 8 patients. In all instances seizure reductions were accompanied by either a decrease in abnormal low frequency activity ( 0 - 7

3P Hz), an increase in deficient middle frequency activity (8--15 Hz), or both. Contingency specific seizure reductions were accompanied by contingency specific EEG changes. These findings indicate that therapeutic changes in seizure incidence following EEG feedback training are associated with significant normalization trends in the sleep EEG. Supported by the Veterans Administration.

9. Wakefulness-sleep modulation of the electrical activity of VPL thalamic nucleus in humans. -- M. Velasco, F. Velasco, C. Cepeda and H. Mufioz (Mexico, D.F., Mexico) Spontaneous and evoked EEG and multiple unit activities were recorded from the VPL thalamic nucleus of a series of patients with intentional and postural tremors, through chronically implanted flexible stainless steel electrodes (diameter 0.0095 in.) used for target localization in the surgical treatment of tremor. VPL nucleus (v.c.i., v.c.e., v.c.p.c.e.) showed peculiar rhythmic (3/sec) EEG activity formed by high amplitude (500--750 pV) sharp waves (similar to the scalp V waves) during paradoxical sleep (PS). These sharp waves appeared isolated during slow wave sleep II and progressively increased in number through slow wave sleep III--IV phases reaching maximum and formed continuous and intermittent patterns during both tonic and phasic PS. This VPL rhythm was accompanied by increased local multiple unit activity and decreased amplitude of late somatic evoked potentials, and showed no temporal relation to the ocular movements or myoclonic jerks of PS. The same rhythm, although with smaller amplitude, was found in nucleus centro medianum thalami (Ce) but was absent in other thalamic (V.o.a., V.o.p., d.o., z.o.) and subthalamic (z.i., Sth., s.n.) structures and scalp regions. Although the physiological significance of VPL rhythm is not known we believed it may be associated with a thalamic mechanism regulating propioceptive sensory-motor integration.

10. The EEG in deep midline lesions. -- N. Schaul, P. Gloor and J. Gotman (Philadelphia, Pa.; Montreal, Canada) To determine the effect of deep midline lesions on the EEG we studied 154 patients with well defined diencephalic, mesencephalic and posterior fossa lesions. Attention was paid to changes in background activity, bilateral paroxysmal slow wave disturbances, and focal abnormalities. Clinical features such as lesion location, state of consciousness, intracranial

4P pressure, and chronicity of the disease process were evaluated. The data were analyzed using computer sorting and the chi square test. The results indicated considerable overlap of EEG abnormalities in lesions from different subcortical sites. Focal abnormalities were relatively specific suggesting a diencephalic lesion. Background activity disturbances were correlated with diencephalic, rostral brain stem, cerebellar lesions, an altered state of consciousness, acute disease processes and increased intracranial pressure. Bilateral paroxysmal slow wave disturbances were the least specific abnormality. There was no value in separating polymorphic from m o n o m o r p h i c or delta from theta paroxysmal slow wave abnormalities. These findings suggest that the diagnostic significance of bilateral paroxysmal slow wave disturbances has been overemphasized in the past. There was no specific feature in this series that helps to clearly distinguish the EEG pattern in deep midline lesions from that seen with diffuse cortical and subcortical encephalopathies.

11. The EEG in a case of complete, isolated, bflataral thalamic d e g e n e r a t i o n . -- S.K. Choi, K.H. Chiappa and R.R. Young ( B o s t o n , Mass.) A 60-year-old previously healthy man died after a 7week illness characterized by dementia, stupor, impaired ocular motility, and myoclonic jerking; all laboratory investigations were normal including a pneumo-encephalogram and bilateral carotid arteriograms, except for a progressive rise of spinal fluid protein. Detailed light microscope examination showed abnormalities confined almost entirely to the thalamus, bilaterally, with extensive destructive lesions of all nuclei of those structures, characterized by neuronal loss, spongy vacuolization of the tissue, astrocytosis, and a hyperplastic and necrotizing angiopathy. (Detailed clinical and neuropathologic features of this case have been previously published by DeGirolami, Haas and Richardson (J. Neurol. Sci., 22 (1974) 197--210.) Two EEGs were done 4 weeks before death and were normal. They showed 50 /~V reactive alpha activity bilaterally at 10 Hz, a small amount of low voltage theta, a good photic driving response at 5/sec, and normal vertex waves and sleep spindles. At 2.5 weeks before death, when the patient was stuporous, the EEG showed generalized 20--50 /~V somewhat rhythmical theta activity. However, stimulation with loud noise or pinch produced a more norreal appearing EEG with posterior predominant symmetrical 30---50/~V activity at 7--8 Hz, and no slower activity. Photic stimulation produced no driving response.

SOCIETY P R O C E E D I N G S This case presents another view of the role of the thalamus in the genesis of normal and abnormal EEG rhythms in humans.

12. Variation of brain stem auditory-evoked r e s p o n s e s ( B A E R s ) as a f u n c t i o n o f ear r e f e r e n c e site: value in resolution and interpretation o f c o m p o n e n t s . -- J.J. Stockard, J.H. Corfits, J.E. Stoekard and F.W. Sharbrough (Rochester, Minn. )

In 50 normal subjects and 50 patients with cochlear or posterior fossa pathology, BAERs were recorded from the vertex (Cz) simultaneously referenced to four different periaural sites: earlobe ipsilateral to acoustic stimulation (Ai) , earlobe contralateral to stimulation (Ac) , mastoid process ( M p ) a n d either high mastoid (Mh) or external auditory canal (EAC) ipsilateral to stimulation. The peak(s) of wave I was always clearly defined in Cz-EAC recordings even when obscured in Cz-A i and Cz-Mp. Waves I and III were selectively attenuated (I p III) in Cz-A c when compared to Cz-Ai. Wave II could usually be identified by its relative preservation between these two attenuated peaks, although Wave III tended to fuse with II in Cz-A c. In contrast to II and III, waves IV and V (normally fused) tended to separate in Cz-A c recordings, the peak latency of IV decreasing and that of V increasing relative to their respective latencies in Cz-A i. This allowed identification and separate measurement of IV and V even in cases where IV and V remained completely fused in Cz-Ai despite the usual measures to separate them. Among ipsilateral external ear references, Mp gave the highest I V / V : I amplitude ratios (<1.0 in only 1% of normal ears), Mh intermediate values, and A i the lowest values (<1.0 in 11% of normal ears). These findings demonstrate the dependence of BAER latency, morphology and amplitude on reference electrode site. Routine use of multi-reference BAER recording has correctly indicated abnormality (or normality) in cases where conventional recordings were non-diagnostic or uninterpretable.

13. Brain stem auditory e v o k e d r e s p o n s e s in spastic d y s p h o n i a . - - F.W. Sharbrough, J.J. Stockard and A.E. A r o n s o n ( R o c h e s t e r , Minn.)

Spastic dysphonia is a disabling and intractable disorder of the voice characterized by moments of involuntary strained-hoarseness and arrests of voice arising from spasmodic hyperadduction of the vocal folds. This disorder has historically been attributed to psychoneurosis, but recent clinical evidence of organic neurologic disease has been found in some patients.

AMERICAN EEG SOCIETY Until now, objective laboratory proof of a neurologic etiology has been lacking. Recently w e found prolongation of latency in farfield brain stem auditory evoked responses in 5 of 10 cases having spastic dysphonia. Because of the small n u m b e r of patients so far examined, the study will be extended to include additional patients within the next several months. Nevertheless, even for the present small sample the findings are significant at a P value of less than 0.01. The presence of abnormal brainstem auditory responses in 5 0 % of patients studied so far raisesthe strong possibility of as yet unidentified brain stem pathology disturbing the innervation of the laryngeal musculature. Although the implication is that certain patients with spastic dysphonia may have a lesion in the brain stem, this is not to say that all patients do, for we may be dealing with a disorder having more than one etiology.

14. The brain stem auditory evoked response (BSAER) in patients with vertigo. -- M.J. Rowe, III (Long Beach, Calif.) In 1977 BSAERs were performed on 82 patients whose chief complaint at the time of testing was vertigo. Test results were correlated with suspected etiology at the time of testing. Abnormal BSAERs were found in 8/25 patients with suspected brain stem vascular dysfunction, in 11/26 with post concussion vertigo, and in 5/8 with suspected demyelinating or degenerative CNS disease. None of 13 patients with suspected labyrinthine disease was abnormal. Abnormalities were seen in 3/10 patients presenting with unusual symptoms. Routine ENG testing was performed on 62 of the patients, with 34 showing abnormalities. In all, the combination of BSAER and ENG testing gave objective evidence for central or peripheral nervous system dysfunction in 53/82 patients.

15. Value o f AEP for detection o f brain stem compression in extra-axial posterior fossa t u m o r s . G.E. Lynn, J. Gilroy and R.L. Maulsby (Detroit, Mich. ) Auditory evoked brain stem potentials were recorded in 12 patients with extra-axial posterior fossa tumors. Recordings from 3 patients with brain stem compression were compared to recordings from 9 patients without brain stem compression. In all 12 cases, click stimulation of the ear ipsilateral to the tumor yielded severely abnormal responses, particularly waves I and II from the auditory nerve and the region of the cochlea nuclei consis-

5P tent with the effects of a mass in the internal auditory canal or cerebello-pontine angle. In the 9 patients without brain stern compression, stimulation of the ear contralateral to the tumor resulted in norreal latencies, amplitudes and wave morphology for all components. Contralateral ear recordings in the 3 patients with brain stem compression revealed abnormally prolonged interwave latencies between waves III and V. Absolute latencies for wave I and the I--Ill interwave latencies remained normal. Post-operatively, the abnormal contralateral III--V interwave latencies returned to normal in two cases studied. W e conclude that abnormalities of wave V recorded from stimulation of the ear contralateralto such tumors strongly suggests the presence of brain stern compression. Furthermore, our results indicate that wave V arises primarily from the side of the brain stem opposite the stimulated ear.

16. A study o f the human visual evoked response using two computer-controlled stimulus parameters. -- J.J. Brickley, J.A. Messenheimer, R.N. Johnson and S.I. Lee (Charlottesville, Va.) A protocol involving two independent parameters of stimulation, which has proven useful in investigating drug effects and pathological mechanisms in animals, was extended to h u m a n visual evoked re.sponses. A series of paired flashes were administered, the first flash of which was given at a fixed intensity. The intra-pairtime interval and intensity of the second flash were varied independently. The evoked responses were determined for three occipital leads, quantified by calculating the rootmean-square ( R M S ) response level over fixed poststimulus periods, and plotted in a three-dimensional format (visual response plane -- VRP). The h u m a n V R P s displayed some characteristics analogous to those observed in sensory and thalamically evoked response planes obtained from animal studies. A n electronic circuit was implemented to measure the light output of the flash tube and calibrate it automatically by computer. Placement of a lightweight, high-speed photodiode on the bridge of the nose allowed computer monitoring of each stimulus administered. Another circuit allowed the computer to set intensity over a wide range and change it between flashes. The V R P protocol allows a reduction in the total number of stimuli required and test duration, making it attractive for clinical research and diagnostic use, and m a y provide a comprehensive measure of dynamic h u m a n cerebral response.

Supported in part by NIH Contract N01-NS-5-2329.

6P 17. Visual evoked responses to stimulus trains: normative data and application to photosensitive seizures and visual disturbances. -- S.I. Lee, J.A. Messenheimer, E.C. Wilkinson, J.J. Brickley and R.N. Johnson (Charlottesville, Va.) Visual evoked responses (VERs) to single flash stimuli demonstrate great variability which poses difficulty in setting up normal ranges. Moreover, in pathological conditions, identification of individual peaks becomes difficult. New stimulation and analysis techniques are needed to overcome these difficulties. There is evidence that functional diturbances of visual pathway or brain itself may show stimulus frequency-dependent changes of VER. In this study, VERs to flash train stimuli (VER-T) were evaluated in 10 normal subjects and 20 patients with disturbances in optic pathways or seizures with EEG photoconvulsive responses. The train length was 250 msec and intra-train interval 1 sec. Each subject was stimulated with 8 different frequency runs (1, 10, 20, 30, 40, 50, 60, 70 Hz). Responses from multiple scalp areas were averaged and analyzed. Normal responses showed consistent early peaks followed by stimulus frequency dependent sequential changes. In light-sensitive seizures, the responses were significantly enhanced, lasted longer, and showed enhanced responses to wide ranges of stimulus frequencies. In visual disturbances, early peaks became inconsistent, delayed or distorted, and late responses altered. These findings were more pronounced than responses to single flash stimuli. It is proposed that VER-T is an effective means to evaluate optic pathway and cerebral excitability changes. Supported in part by NIH Contract N01-NS-5-2329.

18. Alcohol induced changes in flash evoked potentials. -- C.Wm. Erwin and M.I. Linnoila (Durham, N.C.) Flash elicited visual evoked potentials (VEPs) were recorded with 12 young adult subjects. Responses to 40 flashes, with a random inter-flash interval averaging 4 sec, were used to form the average. Ss within 10% of their ideal body weight were administered oral alcohol doses calculated to produce blood alcohol concentrations (BAC) of 0.0 (placebo), 0.04, 0.08 and 0.12 and confirmed by blood alcohol level. Various performance tasks were administered evaluating simple and choice reaction time, short-term memory, tracking and vigilance. A statistically significant dose-response curve was determined utilizing both latency and amplitude features of the N2 and P2 components of the centrally

SOCIETY PROCEEDINGS derived VEP. Previously reported attenuations of amplitude at 0.08 and 0.12 mg% were present with the additional finding of a minor but significant latency prolongation. A significant correlation between VEP changes and performance decrements (Erwin et al., J. Stud. Alcohol, 1978, 39: 505) was present. The consistent amplitude attenuation seen at high alcohol levels was further evaluated using Wiener Filter techniques (Hartweli and Erwin, Electroenceph. clin. Neurophysiol., 1976, 41: 416). Valid VEP estimates were obtained from the first 5 and last 5 of 40 flash presentations during placebo and high dose alcohol conditions. Attenuation is far more pronounced at the end than at the beginning of the 2 rain 40 sec period, indicating a time related effect on VEP amplitude which was significantly modulated by alcohol.

19. Electroretinographie and cerebral responses to pattern reversal and light flash stimulation. A comparative study in normal subjects. -- G.E. Chatrian, P.L. Nelson, R.J. McKenzie, E. Lettich and R.P. Mills (Seattle, Wash.) This study was conducted on 13 normal young adult volunteers without a history of disease of the eyes or the central nervous system and with normal ophthalmological examination and a corrected visual acuity of better than 20/30. Averaged infraorbital electroretinograms and midline occipital responses were elicited by monocular checkerboard pattern reversal stimulation. These potentials were compared with similarly recorded responses to light flashes delivered by a specially built full-field stimulator (Gunkel et al. 1976). Pattern-reversal-elicited electroretinograms were smaller in amplitude and generally bad longer latencies (from onset of shift) than did those evoked by light flashes. A relative large number of trials (384 or more) was needed to demonstrate them. Cerebral flash-evoked potentials included a positive component which resembled the 'P100' wave of the responses to pattern reversal but usually had a longer latency. The possible significance of these differences will be discussed.

20. Lower luminance and the pattern evoked potential in multiple sclerosis. -- B.R. Cant, A.L. Hume and N.A. Shaw (Auckland, New Zealand) Following the finding that patients with possible or probable multiple sclerosis may show an abnormal increase in the latency of the P100 c o m p o n e n t of the pattern visual evoked potential with decreasing lumi-

AMERICAN EEG SOCIETY nance (Cant et al., E l e c t r o e n c e p h . clin. Neurophysiol., 1978, 45: 4 9 6 - - 5 0 4 ) , a further 27 patients with delays at one or b o t h of t w o levels of l u m i n a n c e were reviewed. In 19, P 1 0 0 was delayed at b o t h levels o f luminance following stimulation o f one or both eyes. It was delayed only at the lower l u m i n a n c e in 8 and in n o n e only at the higher luminance. Of the 8 patients with the delay only at the l o w e r luminance, one had definite multiple sclerosis and a n o t h e r m y e l o p a t h y for which no o t h e r cause was found. One had trigeminal neuralgia and 4 had undiagnosed neurological disorders. In the remaining patient, the finding was an artifact due to ptosis caused by ocular myasthenia. No patient with a delay only at the lower luminance had optic neuritis. These results confirm the value of a d i m m e r pattern in detecting abnormalities in patients with no o t h e r evidence of optic n e u r o p a t h y . W i t h o u t an indep e n d e n t m e t h o d of diagnosing multiple sclerosis only t i m e will d e t e r m i n e the specificity of the finding.

21. Visual e v o k e d potentials to pattern reversal in occipital l o b e lesions. - - L.J. Streletz, N.J. Schatz and R.M. R o e s c h m a n (Philadelphia, Pa.) R e c o r d i n g of visual e v o k e d potentials (VEPs) to pattern reversal is considered a reliable diagnostic procedure for evaluating patients with anterior visual p a t h w a y lesions. A s y m m e t r i c a l VEPs have been described in patients with m o r e posterior lesions a c c o m p a n i e d by h e m i a n o p i c field defects ( B l u m h a r d t et al. 1977). Since less consistent results have been r e p o r t e d in o t h e r studies of patients with lesions in this area, VEPs were r e c o r d e d to pattern reversal in 20 patients in w h o m clinical e x a m i n a t i o n visual fields and c o m p u t e r t o m o g r a p h y indicated occipital lobe pathology. The VEPs were o b t a i n e d f r o m each eye with recording electrodes located transversely over the t e m p o r o - o c c i p i t a l region (Ts, O1, Oz, 0 2 , T6) with a frontal (Fz) reference site. The p a t t e r n e d screen reversed at 2/sec and s u b t e n d e d 30 ° of the visual angle. The analysis t i m e was 200 msec and 128 responses s u m m a t e d . The VEP wave f o r m , peak latencies and distribution were r e c o r d e d and c o m p a r e d with the l o c a t i o n of the occipital l o b e lesion(s) and visual field defect(s). With this t e c h n i q u e , a m a x i m a l VEP response (P99) was r e c o r d e d at the scalp electrodes situated over the involved occipital lobe and contralateral to the h e m i a n o p i c visual field defect. Thus, a positive correlation of occipital lobe damage, h o m o n y m o u s field loss and VEPs was m a d e in this series of patients.

7P 22. Variability of the visual evoked p o t e n t i a l during the first year o f life. -- J.F. Peters, R.J. Ellingson and J.L. Varner (Omaha, Nebr.) Visual evoked potentials ( V E P s ) t o stroboscopic flashes were r e c o r d e d f r o m full-term, p r e m a t u r e and trisomy-21 infants during the first w e e k of life and at 1, 3, 6 and 12 m o n t h s of age. Ongoing brain electrical activity and the VEP were r e c o r d e d f r o m O1, Oz, 02, C3, C z and C4 referred to ipsilateral ear electrodes and stored on FM tape. The ongoing E E G was scored for sleep stage and the presence/absence of artifacts during the stimulus period. One second artifact free epochs following each of 30 flashes were sampled and stored on a PDP-12. The 30 epochs were divided into 6 successive blocks of 5 flashes each. Averages were calculated for each block and over all 30 epochs for the occipital electrodes. In general the block-of-5 VEPs were consistent a m o n g themselves and very similar to the block-of-30 VEPs. There was no evidence of h a b i t u a t i o n or fatigue effects in any series of VEPs for any group. N1 and P2 latencies showed relatively s m o o t h and systematic decreases with age in all groups. N2 and P3 latencies h o w e v e r were quite variable, particularly at 6 and 12 m o n t h s of age.

23. A b n o r m a l i t i e s of visual e v o k e d r e s p o n s e s in infants with hydrocephalus. -- A.L. Ehle and F.H. Sklar (Dallas, Texas) In order to evaluate the usefulness of evoked potentials in the evaluation of infants with disease affecting the cerebral hemispheres, visual evoked responses (VERs) were studied in 15 infants less than 6 m o n t h s of age with a diagnosis of hydrocephalus. Patients with a history of meningitis were e x c l u d e d and h y d r o c e p h a l u s was d o c u m e n t e d by p n e u m o e n cephalogram of CT scan. V E R s were r e c o r d e d f r o m Ot and 02 referentially to C z. X e n o n flash stimuli were delivered at a rate of 0.25 or 0.5 Hz. Patients were studied during the waking state to avoid variations in response that m a y occur with change in state or consciousness. The latency of the m a j o r positive c o m p o n e n t (P2) was measured and c o m p a r e d with P2 latency of normal controls of similar gestational age. In 11 of the 15 h y d r o c e p h a l i c infants the P2 latency was greater than one standard deviation longer than age m a t c h e d normals. In 8 infants w h o were studied i m m e d i a t e l y prior to shunting and then one week later, a 32 msec decrease in P2 latency was n o t e d to occur. The results of these studies suggest t h a t visual evoked responses m a y be a clinically useful m o n i t o r o f cerebral f u n c t i o n in infants for both the d e t e c t i o n of a b n o r m a l i t y and to m o n i t o r the effectiveness of the therapy.

8P 24. Patterned VEPs in normal and MCD children. -S.J. Purves, M.D. Low, L. Rogers and H.G. Dunn (Vancouver, Canada) The visual evoked potential (VEP) elicited by a reversing-pattern stimulus has become a fairly commonly employed measure of visual function. To date, the latency of the first major positive peak of this VEP has received widespread acceptance as a measure of delayed conduction in compressive, ischemic or demyelinating optic neuropathies, but there has been little attention paid to its application in assessing cortical function. The results reported here were obtained from a group of 14-year-old children who were subjects in a long term prospective study of low birth weight infants. There were 37 children in the normal group and 17 with the diagnosis of minimal cerebral dysfunction (MCD). The latency of the major positive peak of the pattern VEP was not significantly different between the two groups. However, there was a marked difference in the symmetry of the VEP amplitude in the occipital regions between the normal and MCD children. The peak-to-peak amplitude of the P l l 0 to N160 c o m p o n e n t was significantly lower in voltage over the left hemisphere than the right in the MCD children, but in the normals there was no such asymmetry. These findings support the concept that pattern VEPs may reflect cortical function as well as optic nerve or tract activity and may, along with other electrophysiological measures, be useful in the differential diagnosis of MCD. 25. Somatosensory cerebral, far-field and spinal evoked potentials in children with degenerative diseases of the central nervous system. -- J.B, Cracco, V.V. Bosch and R.Q. Cracco (Brooklyn, N.Y.) Spinal and cerebral evoked potentials to peroneal nerve stimulation were recorded from the spine and scalp of 15 children with CNS degenerative diseases (Tay-Sachs, 10 patients; Canavan's, 2; Sandhoff's, 1; Gin3 gangliosidosis, 1; Sanfilippo, 1). Median nerve evoked short latency (far field) and longer latency potentials were also recorded from the scalp. Response wave form and conduction characteristics were compared with those of age-matched normals. In all patients conduction velocity over peroneal nerve was normal. Responses were recorded over the spinal cord, but conduction velocities over the cord were slowed. Cerebral responses to peroneal nerve stimulation were absent in all but one patient. In normal subjects, 3 short latency positive potentials evoked by median nerve stimulation are recorded from the scalp. These probably arise in peripheral

SOCIETY PROCEEDINGS nerve, spinal cord-brain stem, and brain stem-diencephalon, respectively. In most patients only the first two potentials were recorded. The third positive potential and subsequent potentials of cerebral cortical origin were absent. These findings suggest that in certain degenerative disorders there is a rostral-caudal deterioration of CNS function. This study demonstrates that these methods permit an evaluation of the entire neuraxis from peripheral nerve to cerebral cortex. Supported by Research Grant NS 12039 USPHS. 26. Short latency somatosensory evoked responses (SERs) in patients with neurological l e s i o n s . K.H. Chiappa, S.K. Choi and R.R. Young (Boston, Mass.) Following median nerve stimulation at the wrist, SERs were recorded using a 4-channel montage, each derivation being selected for best demonstration of the activity at a given level of the sensory pathways from peripheral nerve to cortex (braehial plexus, brain stem, thalamus, thalamocortical radiations, cortex). Normative data obtained from 25 subjects will be presented. A group of 150 patients with neurological lesions were studied; the SERs obtained from some with discrete, clinically well-localized lesions will be presented. The patterns of alterations of their SERs suggest origins for some of the major wave forms entirely different from those so far postulated. It has been suggested by Cracco and Cracco (Electroenceph, clin. Neurophysiol., 1976, 41: 460--466) and Kritchevesky and Wiederholt (Arch. Neurol. (Chic.), in press) that their third positive wave (P15) arises in the thalamus; Jones (Electroenceph. clin. Neurophysiol., 1977, 43: 853--863) thought his N14 (probably the same wave as P15 mentioned above recorded with different derivation) arises in the thalamus or brain stem. Three of our patients with thalamic hemorrhages and one with a midbrain hemorrhage, all of whom had severe clinical sensorimotor deficits, had normal wave forms at those latencies, suggesting that this component is generated below the midbrain. We also will present evidence from these patients and the literature (especially from stereotactic thalamotomies in humans) which suggests that N20 arises in the thalamus and not the cortex. These results have direct bearing on the clinical interpretation and utility of SERs. 27. Depth electrode recording of the VER from the geniculate region in man. -- J.-P. Spire and Y. Hosobuchi (Chicago, Ill. ;San Francisco, Calif.) A 37-year-old man underwent a stereotactic implantation of a multiposition depth electrode in the

AMERICAN EEG SOCIETY left internal capsule for attempt of relief of post-traumatic phantom-limb pain. The inferior position of the electrode was found to be actually in the left optic radiation 4 turn anterior to the lateral geniculate body. Electrical stimulation of the inferior electrode position produced photopsias described by the patient as a 'checkerboard-like' effect of black and white dots which increased in brightness as the intensity of the stimulus was increased. The photopsias occurred in the right inferior visual quadrant. Recording the xenon flash averaged evoked response from this site demonstrated a 22--23 msec latency to onset, which occurred just at the onset of the ' B ' wave of the ERG. This is further direct evidence of the long electrical latency of the pregeniculate visual pathway and supports the presumption that intraretinal processing accounts for a significant proportion of the delay of the initial lateneies of the scalp recorded human VER.

28. The human amygdala. Elect~ophysiological r e s p o n s e s t o o d o r a n t s . -- J.R. Hughes and O.J. Andy (Chicago, Ill.; Jackson, Mo.) Nine patients had an amygdalotomy for attempted relief of intractable seizures and, as an aid for localization, recordings were made from the amygdala and later were computer analyzed. The background activity is 3--18 c/sec; in response to odorants sinusoidal bursts are seen, synchronous with inspiration at 12--24 c/sec, but mainly at 40--70 c/sec. Each odorant is associated with a given group of frequency components. However, for many different odorants the number of these components is restricted and the hypothesis is presented that odor discrimination in man's amygdala is not determined by which components are present, but the patterning of the components according to their amplitude. Odorants within the same odor class produced similar patterns of response. Epileptiform activity was recorded in two different forms, one in response to odors, similar in frequency to the slower bursts, except for sharper configurations, at times progressing to clinical seizures and the second as an insertion discharge from an advancing electrode, similar in frequency to the faster bursts. These latter data suggest that the repertoire of a given neural system or structure may be limited to specific frequencies but the configuration or patterning of these frequencies defines the different states of the structure.

9P 29. Intracranial distribution of the P300 c o m p o n e n t of human somatosensory and auditory evoked potentials. - - C.C. Wood, T. Allison, W.R. Goff, P.D. Williamson and D.B. S p e n c e r (West Haven, Conn.) When recorded from the scalp, the P300 component is a large-amplitude positive potential with 300--400 msec latency and maximum amplitude focus in the midline centro-parietal region. Unlike shorter latency components, P300 is relatively insensitive to stimulus characteristics but depends primarily upon the psychological context in which a stimulus occurs. Here we report preliminary results of P300s recorded from chronically implanted multicontact depth electrodes. These data were obtained with informed consent in conjunction with clinical EEG recordings to evaluate possible neurosurgical intervention in five patients with intractable epilepsy. Each patient had either three or four depth electrodes, which entered the brain from the frontal, fronto-central, or parieto-occipital regions and were directed toward the temporal poles or medial orbitofrontal cortex. Results were: (1) As previously reported for depth potentials coincident with the scalp-recorded vertex potential (Goff et al., in press), maximum P300 amplitude occurred relatively deep in the brain, not near the cortical surface. (2) There was no evidence of the polarity inversions that might be expected if P300 were cortically generated. (3) Potentials having morphology and amplitude distribution consistent with P300 were observed from depth electrodes in some patients without clear concomitant P300s at the scalp. Although additional information is necessary, these data are difficult to reconcile with a cortical origin of the P300 component. Supported by the Veterans Administration and NIMH Grant MH-05286. 30. Comparison o f somatosensory evoked short latency potentials in m a n and cat. -- M.H. Feldman and R.Q. Cracco (Brooklyn, N.Y.) Somatosensory short latency (far field) potentials were recorded from the cerebral dura in eats using the same recording methods employed in man. Components in cat and man were correlated. In cats, the location of co m p o n en t generators was assessed by observing the effects of CNS ablations and extensive rhizotomy on each component. The pre- or post-synaptic origin of components was determined by studying the effects of rapid rates of repetitive stimulation and asphyxia on each component. In man these responses consist of three positive potentials, the third of which is often bilobed. The first potential in man corresponds to an initial usually

10P bilobed positive potential in the cat. The first lobe arises in proximal segments of stimulated peripheral nerve fibers and the second in pre-synaptic cervical cord afferent pathways. The second positive potential in man corresponds to the second positive potential in cat which arises in post-synaptic cervical cord and brain stem elements. The third bilobed positive potential in man corresponds to the third and fourth positive potentials recorded in cats which arise in the posterior fossa and in subcortical supratentorial structures, respectively. Supported by Research Grant NS 12039 USPHS.

31. Somatosensory evoked short latency potentials in brain dead patients. -- B. Anziska and R.Q. Cracco (Brooklyn, N.Y.) In normal adults, the short latency (far field) evoked potentials to median nerve stimulation at the wrist consist of three positive potentials with peak latencies of about 10, 12 and 15 msec. These three potentials are thought to ~ise primarily in peripheral nerve, spinal cord-brain stem and brain stem-diencephalon, respectively. These are followed by a negative potential with a peak latency of about 20 msec which is thought to reflect the arrival of the volley in specific somatosensory cortical elements. Abnormalities of these potentials have recently been described in the majority of a group of patients with multiple sclerosis (Anziska et al., in press). These potentials were studied in 8 patients who fulfilled all the clinical criteria for brain death. In all patients the first positive potential was present. In three patients all subsequent potentials were absent. However, the second positive potential was recorded in two patients, the third positive potential in three patients and the first negative potential in one patient. Later cortical potentials were not observed in any patient. These results show that the integrity of certain central somatosensory afferent pathways may be preserved in some patients who fulfill the clinical criteria for a diagnosis of brain death. Supported by Research Grant NS12039 USPHS.

32. Cerebrocortical death vs. brain death: correlation o f clinical, EEG, and evoked potential studies. -M.A. Pollack and P. Kellaway (Houston, Texas) Loss of clinically and electrophysiologically detectable cerebroeortical function with preservation of brain stem reflexes followed acute neurological disorders in 5 patients ranging in age from 2 weeks to 60

SOCIETY PROCEEDINGS years. Physical findings in all patients included spontaneous respiration, conjugate nystagmoid movements in the absence of visual following and a nonhabituating cochleopalpebral response. Serial iso-electric EEGs satisfying the American EEG criteria for cerebral death recording were obtained in all patients. Difficulties in recording and interpretation resulted from preservation of reflex eye movement, chewing, swallowing, and myogenic and tongue artifact. These problems are not encountered in brain death, where brain stem as well as cortical function has ceased. Evoked potential (EP) studies supported neurological and EEG findings in all 5 patients: auditory brain stem EPs were preserved while cortical EPs were not elicited by auditory, photic, or somatosensory stimulation. In brain death, on the other hand, absence of brain stem EPs as well as cortical EPs has been shown. These studies demonstrate that prolonged survival with preservation of vital functions occurs in patients with continuously iso-electric EEGs and that EP studies may help to establish a localizing diagnosis in such individuals.

33. Evoked potential somnogram in sleep and coma monitoring (human and animal studies). - - R . G . Bickford, D. Karnaze, R. Hajdukovic and J. Franke (La Jolla, Calif.) In spite of extensive EEG studies in animal and man, localization of lesions in cases of clinical coma remains unsatisfactory. However, if data from evoked potentials (brain stem and cortical) are combined with long-term EEG spectral monitoring (somnogram), a more incisive tool for lesion localization, clinical diagnosis, and prognosis is available.

Technique Spectral studies use Medilog tape system (4 channels) allowing 16 h recording with × 60 playback into the PDP/11-40. Evoked potential somnogram is generated on-line with PDP/12 system.

Results Animal. Evoked potential somnograms have been recorded, with normals (10), in coma model rats (anesthesia, anoxia, etc.). Human. These integrated coma tests have been carried out as follows. (1) All night somnograms on 20 normal subjects with continuous auditory or visual evoked potential monitoring form the normal subject basis for interpretation of the clinical material. (2) Twenty cases of clinical coma have yielded the following varieties of findings: (a) absent BAER and A E R ; (b) normal BAER, absent A E R ; (c) normal BAER and AER. This 'pathway' information is interpreted in relation to spectral evidence (presence of

AMERICAN EEG SOCIETY cycling or m o n o r h y t h m i c patterns, specific patterns -- alpha, theta, spindle, augmenting, etc.). This data assists in localizing the particular lesion to brain stem, midbrain or cortex. Supported by NIH PHS-NS-08962-10.

34. Flurazepam-induced changes in cerebral electrical activity. -- P. Naitoh, D.M. Seales, L.C. Johnson and M.W. Church (San Diego, Calif.) To further study the effect of flurazepam on sleep EEG activity, history and EEG criteria were used to select 12 male poor sleepers (mean age 21.3 years). After 2 screening nights, all 12 subjects were given placebo capsules for 7 nights. For the next 10 nights, 6 subjects were given 30 mg of flurazepam and 6 continued to receive placebo. Three placebo follow-up nights were run 2--3 weeks post-drug. C3-A1+A2 activity was analyzed from uninterrupted sleep nights by an on-line alpha, delta and spindle detector and off-line by a PDP-12 computer. T wo baseline (placebo) and 4 drug nights were available for analysis. To measure the ERP from C3 to linked mastoids, a 44 dB SPL, 10 msec click was administered once every 32 sec throughout the last placebo and last drug nights. In NREM sleep (stages 2, 3 and 4), flurazepam increased spindle rate per rain by 72%. Wave-by-wave zero-crossing analysis revealed a significant decrease in delta amplitude and a significant decrease in number of delta waves. Delta period was not changed. There were less changes in delta activity during REM. The ERPs were indistinguishable from the K-complex in morphology. Both within- and between-group analyses indicated that flurazepam significantly lowered sleep ERP amplitude.

3 5 . A n alternative t o EEG signal-averaging when t h e number of evoked potentials is small or w h e n s t i m u l u s t i m i n g is u n k n o w n . - - B. Saltzberg

(Houston, Texas) A problem frequently encountered in the use of averaging to aid in the detection of event related EEG potentials (ERP) arises from the fact that either the number of event replications is small (i.e. few stimuli) or the times of occurrence of the stimuli are unknown. In small children or in certain animal experiments the constancy of state may be limited to a time period so small that it is not possible to present a sufficient number of repetitions of the stimulus to make averaging an effective detection procedure. In some experimental designs prior knowledge of the timing of stimulus events is not possible and this precludes

llP the use of averaging to determine the presence of the ERP. This situation occurs in experiments which are concerned with the detection of ERPs resulting from spontaneous stimulus events (such as deep brain electrical spikes) that are not under direct experimental control. Under these conditions it is frequently possible to detect the presence of ERPs without averaging. The alternative to averaging is based on the morphology of high resolution power spectral densities (PSD). This paper will describe the constraints of the method and will present illustrative test data to demonstrate how the presence of weak ERPs in very noisy backgrounds can be inferred from PSD morphology. This research partially supported by the Office of Naval Research under Contract No. NR 207-011. 36. Clinical significance of periodic EEG patterns. -Y. Kuroiwa and G.G. Celesia (St. Louis, Mo.) Periodic patterns defined as stereotyped paroxysmal transients separated by nearly identical intervals were studied in 56 patients. Periodic patterns were subdivided into generalized and focal. Generalized periodic patterns were classified into suppression bursts (10 cases): bursts of polymorphous transients alternating with periods of relative quiescence; paroxysmal complexes (16 cases): transients are high amplitude slow/sharp waves; repetitive sharp transients (1 case): bilateral synchronous spike/ sharp waves at frequency less than 2/sec with attenuated background activity between transients; triphasic waves (8 cases): triphasic sharp waves with bifrontal predominance. Each of the 21 cases of focal periodic patterns were classified as PLEDS. Generalized periodic suppression bursts occurred in anoxic/metabolic encephalopathies, anesthesia and drug intoxication. Suppression bursts following cardiorespiratory arrest carried a poor prognosis. Generalized periodic paroxysmal complexes were observed in anesthesia, drug intoxication, anoxic/metabolic encephalopathies. When these conditions were excluded they indicated the diagnosis of SSPE or other viral encephalitides. Periodic triphasic waves occurred only in anoxic/ metabolic encephalopathies. Repetitive sharp transients were observed in one case of anoxic encephalopathy. PLEDS were associated in 19 cases with clinical seizures and were caused by various pathologies. 37. Routine electroencephalograms and I.Q. scores at age 7 - 8 years. -- R. Engel (Portland, Ore.) The study is part of the nationwide Collaborative Perinatal Project. In Oregon, 402 children bad routine

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neurological, psychological and e l e c t r o e n c e p h a l o graphic e x a m i n a t i o n s at school age. T h e classification o f the E E G based on degree of a b n o r m a l i t y and organization of background activity correlated significantly with neurological o u t c o m e and I.Q. test scores, b u t it was n o t possible to link statistically any specific grapho~element with intellectual deficiency. Failure o f alpha blocking u p o n opening o f the eyes, however, and absence of ' f o l l o w i n g ' during p h o t i c driving p r e d i c t e d lower I.Q. scores. In their overall o u t c o m e the E E G s o f survivors with high risk perinatal factors were at 7 years statistically n o t significantly different f r o m the n o r m a t i v e group, in which the high risk factors at birth were absent.

38. N e u r o e l e c t r i c m a n i f e s t a t i o n s of c o m p l e m e n t a r y hemispheric specialization in an e x p e c t a n c y task. -- C.S. Rebert, R. L o w and J. Hatchel (Menlo Park, Calif. ) Ss were tested in a reaction t i m e ( R T ) task wherein warning stimuli (WS) were briefly presented 5-letter words or d o t p a t t e r n s i n t e r m i x e d across trials. A f t e r 2 sec an imperative stimulus (IS) of the same category as the WS appeared and the S pressed a key with the left or right hand. The right key was pressed if the IS w o r d was a s y n o n y m of the WS or if the IS pattern was the same as the WS pattern. The left key was pressed for a n t o n y m s or different patterns. It was predicted that CNVs w o u l d be larger over the left than right hemisphere on w o r d trials and vice-versa on pattern trials in accordance with speculations concerning hemispheric specialization. The CNV was lateralized as e x p e c t e d , m o s t p r o m i n e n t l y on pattern trials. Also, a negative transient p o t e n t i a l (possibly N1) and a late post-imperative slow wave were similarly lateralized. P300 waves were larger to the IS w h e n it differed f r o m the WS, but P300 e x h i b i t e d no lateralization. T h e lateralized C N V m a y be c o n s t r u e d as a differential a t t e n t i o n a l set. Lateralization of N 1 is c o m p a t i b l e with such an i n t e r p r e t a t i o n as it appears to reflect a t t e n t i o n to p a r a m e t e r s t h a t define an i n p u t channel.

39. EEG A.S. ling, (San

correlates o f higher cortical functions. -Gevins, J.C. Doyle, G.M. Zeitlin, C.D. YingR.E. Schaffer, E. Callaway and C.L. Yeager Francisco, Calif.)

As a prerequisite to possible use of the E E G for the assessment of subtle patterns of cortical dysfunction, t w o studies were c o n d u c t e d . S t u d y 1 used a battery of c o m p l e x 'logical' and 'spatial' tasks. S t u d y 2 e m p l o y e d simpler tasks w i t h o u t l i m b m o v e m e n t s and c o n t r o l l e d for differences in stimulus characteristics and performance-related factors.

In each study, 8 channel E E G s f r o m approxim a t e l y 20 normal, right-handed adults were analyzed (total of a p p r o x i m a t e l y 20 min per task). Artifactc o n t a m i n a t e d data were eliminated. F e a t u r e s based u p o n the p o w e r s p e c t r u m were c o m p u t e d . Two-stage, nonlinear multivariate pattern recognition was used to classify the E E G with its associated task. Task-to-task discrimination, strong in study 1, was weak in study 2, suggesting that e f f e r e n t activities, stimulus characteristics and performance-related factors of tasks are m o r e p r o m i n e n t in the EEG than cognitive aspects of tasks. T h e m a g n i t u d e (approx. 10%) and a n a t o m i c distrib u t i o n (diffuse, e x c e p t frontally) of the r e d u c t i o n of alpha and beta band intensity were remarkably similar for the controlled tasks. T h e t a band intensity was slightly increased. There was no evidence in these results that 'logical' and 'spatial'cognitive functions are associated with lateralized E E G patterns. Supported in part by U S P H S RR05755.

Grant N S 1 0 4 7 1

and

40. Dimensions of volitional c o n t r o l over interhemispheric coherence of the EEG. - - J. B e r k h o u t and D.O. Walter (Vermillion, S.D.; Los Angeles, Calif.) Volitional control of interhemispheric coherence b e t w e e n parietal and occipital areas was studied at 6, 10 and 14 Hz in 5 subjects, using a real-time display of interhemispheric coherence. D i f f e r e n t center frequencies and electrode configurations p r o d u c e d different interhemispheric c o h e r e n c e patterns, showing variations in the range of c o h e r e n c e values displayed, the effectiveness of particular behavioral strategies in m o d i f y i n g the display, and the m a g n i t u d e and direction of shifts in c o h e r e n c e c o n t i n g e n t on such behavior. Behavior tending to increase levels of arousal was observed to increase interhemispheric coherence b e t w e e n occipital areas at 6 and 14 Hz, and to decrease such c o h e r e n c e at 10 Hz. C o h e r e n c e b e t w e e n parietal areas was less amenable to behavioral control. No behavioral e f f e c t on parietal coherence was n o t e d at 6 and 14 Hz. Parietal coherence at 10 Hz diminished as arousal increased, but this e f f e c t was less clear and consistent than the shifts in coherence with changes in arousal that were observed b e t w e e n occipital areas. 41. A n e w m e t h o d for detecting clinically i m p o r t a n t features of visual e v o k e d potentials. -- J.L. Gedye, R.L. Maulsby and J.B. Z u c k e r m a n (Detroit, Mich.) Traditional approaches to quantitative analysis of VEP waveforms, which have relied on d e t e c t i o n of

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named peaks and measurements of their latency, are of limited value in clinical applications where the waveform becomes so distorted by pathological processes that such peaks cannot be identified with certain ty. T o meet this difficulty we are developing an approach in which the original VEP waveform undergoes transformations which allow easier quantification of its clinically important features. The waveform is normalized by expressing each of its points as a deviation (+ or --) from their mean, and scaling them so that unit total area is included between the wave and its baseline. From this representation separate cumulative curves for the equal +ve and -- ve components are formed. In normal subjects the time by which 50% of the +ve c o m p o n e n t has been generated approximates the latency of the major positive peak as traditionally measured. The approach has been applied to a study of intersex differences. This work was supported in part by NIH Grant Number 05384-17.

42. Clinical value of computer-assisted VEP analysis. - - R.L. Maulsby, N.R. Russ, J.B. Zuckerman and J. Gilroy (Detroit, Mich.) A program for computer evaluation of patternreversal visual evoked potentials has been in routine clinical use at Harper Hospital since October 1977. The program operates as follows: 4 channel VEPs recorded on magnetic disks are displayed on an oscilloscope, and 2 cursor beams are moved by the technologist along each channel, bracketing the major positive peak by the preceding and following negative deflections. The computer then determines the point of maximum positivity between these two negative cursor points and stores this data obtained from two trials of monocular stimulation of each eye. The results obtained from the patient are then compared to a stored table of normal values of expected latencies, voltages and their standard deviations previously obtained from 30 control subjects. Each patient's results are printed out, along with channel-by-channel deviations from the mean normative values, if these exceed 1 standard deviation. Latency and voltage differences between the two eyes are also calculated, and the two trials from each eye axe compared using the Pearson correlation coefficient method. We have found this system to be quite useful clinically, reducing subjectivity and adding quantification to our interpretations. We will demonstrate its results in a wide variety of clinical conditions including demyelinating disorders, tumors and traumatic disturbances of the optic pathways.

13P 43. A new method for automated evoked potential analysis. -- G.K. Morley and K. Liedke ( M i n n e a p o l i s , Minn.) The use of multivariate statistics allows simultaneous analysis of a large number of variables. When applied to evoked potential analysis, it allows the use of the same criteria to assess evoked potentials from heterogenous groups of patients. The technique in this paper was applied to discriminate lesions in various lobes of the brain using brain scan and clinical criteria of aphasia. It does, however, have general value in finding the most discriminative wave forms for any two or more groups. An automated peak and latency detection algorithm allows absolute objective data analysis. It has usefulness for all fields of evoked potential analysis in drug studies, auditory evoked potential assessment in coma, and detection of optic involvement in M.S. Almost one to one correlation of manual versus automated programs point out its reliability. 44. Separating several-cell records into several singlecell records. -- D.O. Walter (Los Angeles, Calif.)

W.B. Marks submitted for publication a method for separating non-Gaussian stochastic variables from recordings of a sufficient number of their mixtures. I extended that method to stochastic processes, hoping to separate single-unit records from mixtures of several cells' outputs. The method demands rapid sampling and m u c h computation, since it depends on records' spectra and bispectra (and cross-spectra and cross-bispectra, if available). Because of the high computational cost, the method will be most applicable to especially valuable records, perhaps from neurosurgical patients. M a n y other separation methods have particular difficulty in separating superpositions, at many slightly different firing times, of action potentials from the same limited number of cells. The Marks method, in contrast, should function particularly well in analyzing such records, since one of its constitutive assumptions is that action potentials from different cells will fire at approximately independent times. Dr. C.J. De Luca of Children's Hospital, Boston, has kindly provided some two-wire electromyograms, sampled at 65 kHz per channel. I plan to compare results from the Marks method with De Luca's results, using a quite different pattern recognition method. Pilot programs for the first steps of the extended Marks method have been tested out, and show that the sample spectra and bispectra (and cross-spectra and cross-hispectra) do indeed allow separation of mixtures of two cells' potentials. More realistic (though still artificial) mixtures will be input to the next steps of m e t h o d development.

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SOCIETY PROCEEDINGS

45. Toward an ideal non-cephalic reference. -- J. Dubinsky, J.S. Barlow and H.J. Lander (Boston, Mass. )

47. Long-term effects of valproic acid on spike and wave discharges. -- J. Bruni, B.J. Wilder, L.J. Willmore and H.J. Villarreal (Gainesville, Fla.)

One of the oldest problems in EEG is that of the ideal reference. Cephalic references can introduce uncertainty as to the exact source of a particular waveform, whereas non-cephalic references can introduce artifactual components such as EKG or EMG. Implementing the scheme of EKG subtraction by computer suggested by Bickford et al. (Proc. San Diego Biomed. Syrup., 1971, 10: 117--123), we have developed a system for on-line (or off-line, from magnetic tape) subtraction of a relatively stereotyped EKG artifact from 15 or 16 channel (or more) clinical recordings. A PDP-12 computer triggered from the R-wave initially averages 20--60 EKG waveforms for all incoming channels. A running subtraction of the resultant averages from the respective EEG channels then essentially eliminates the EKG artifact in the EEG of the final ink-recording. It is expected that this technique may be useful in computer analysis of EEG data (for example in generating topographic displays) but also in clinical EEG, particularly in those instances (such as in recordings in small children and in the obese) in which EKG artifact-free non-cephalic referential recordings may be desirable but difficult or impossible to obtain.

Twenty-five patients with absence seizures were treated with valproic acid in doses ranging from 17 to 62.5 mg/kg/day. Six hour telemetered EEGs were obtained at the onset of the study, 2 weeks after placebo lead-in and 10 weeks after active therapy. Fifteen patients have been followed for one year. EEG analysis was carried out to determine the longterm effects of valproic acid on the number and duration of spike and wave discharges. Changes in hackground activity were also evaluated. EEG changes were correlated with plasma valproic acid concentrations and clinical response. Patient reaction times were assessed to determine the clinical significance of individual spike and wave discharges of varying duration. Data will be presented to show the long-term effects and compare these to the short-term results at the end of 10 weeks of valproic acid therapy.

46. The significance of head turning in focal epilepsy and the effect of the state of alertness in the development of a clinical seizure as evaluated by a new time-lapse video monitoring system. - - J . R . Ives, P. Gloor, T. Rasmussen and A. Olivier (Montreal, Canada) An audio/video system has been developed which can continuously m o n it o r the clinical activities of an epileptic patient without intervention for more than 24 h. This system is time-locked to the existing cabletelemetry EEG seizure monitoring system to enable complete documentation of the EEG and the clinical activities associated with the patient during a spontaneous seizure. Over 100 patients have had one or more of their seizures recorded in this manner. The equipment, its application and methodology will be shown, demonstrated and discussed. EEG tracings will also be available for viewing and discussion. Playback of the actual video recordings of selected seizures will be made as related to the following: (1) the significance of head turning has been evaluated in a group of patients with established temporal lobe epilepsy, (2) the significance of preseizure state of alertness (awake or asleep) has been evaluated in another group of patients with stereotype EEG seizure patterns.

48. The EEG in ictal pain. -- G.B. Young and W.T. Blume (London, Ont., Canada) Pain as a symptom of cerebral seizures has received scant attention in the literature since Gowers' description in 1881. Ten of 414 epileptic patients (2.4%) described pain as a symptom of their seizures. Postictal pain was excluded. Pain occurred over the calvarium (cephalic group) or unilaterally in the face, arm or leg (non-cephalic group). Four of the 5 patients in the non-cephalic group had electrographic seizures arising from the central parietal region contralateral to the pain. Spikes occurred in the posteentral gyrus at electrocorticography in the two patients who had surgery. Resection of the area abolished the ictal symptoms in both cases. In the cephalic group, clinical analysis revealed that all 5 patients had focally originating seizures but from different cortical areas. There was no relationship between the presumed site of seizure origin and the site of pain. Epileptiform activity occurred in the occipital region (3 patients), parietal region (2 patients), temporal region (1 patient) and central region (1 patient). We conclude that non~ephalic unilateral pain implicates the contralateral central parietal region but cephalic pain has unreliable localizing value. 49. Changes in the human EEG in association with exposure to high ambient pressure. -- J.E. Bevilacqua and J.O. Donaldson (Philadelphia, Pa.) Serial scalp EEG recording was conducted on appropriately trained professional deep sea divers

AMERICAN EEG SOCIETY who were subjected to progressive increases of ambient pressure in a hyperbaric chamber to levels equivalent to a depth of 1600 ft. of sea water (FSW). The results of the electroencephalographic study of four of these divers will be presented. Definite changes were observed in the EEG as pressure was increased beyond 640--800 FSW. In general, these were progressive with depth and included: (1) disorganization of background activity and apparent lowering of frequency of components of background activity in all subjects; (2) the occurrence in all 4 subjects of intermittent irregular forms as low in frequency as 1.25 Hz. These occurred bilaterally as well as asymmetrically, more frequently over the frontal and central areas and to a lesser extent the posterior temporal regions; (3) lower frequency activity which was more overtly paroxysmal, especially over the frontal areas in all divers. There was no apparent direct correlation of most of the electroencephalographic observations with clinical phenomena.

50. Correlations between EEG and cerebral blood flow in the rabbit. -- C.V. de Bl~court and J. Smith (Amsterdam, The Netherlands) EEG of the visual cortex was recorded in 15 rabbits. Artifact-free samples, corresponding to the first minute of brain clearance of intra-arterially injected 133-Xe, were analyzed with: aperiodic amplitude interval analysis (AAIA), analogue filter frequency analysis ( A F F A ) and spectral analysis (FFT). The following quantitative coefficients of correlation between EEG and mean cerebral blood flow (CBF) (bicompartmental analysis) were obtained. AAI A: mean interval length: --0.53 (P < 0.05). Coefficient of variance of the mean interval length: --0.61 ( P < 0.05). A F F A : % d e l t a : - - 0 . 6 6 ( P < 0.005); % theta: 0.70 (P < 0.005). F F T : % delta: --0.72 (P < 0.005); % theta: 0.72 (P < 0.005); dominant frequency: 0.76 ( P < 0.0005); delta-theta power median, defined as the frequency corresponding to the half-power in the 1--7.5 c/sec range: 0.86 (P < 0.0005). We consider the degree of arousal during the CBF measurement the physiological basis for these results. CBF increase during arousal is generally accepted. During arousal, the resting EEG becomes intermingled with volume-conducted theta waves of hippocampal origin. When mainly theta waves are present, this can be clearly demonstrated with the A F F A method. A gradual change-over, however, from a resting EEG pattern, to a picture dominated by theta waves, is detected more specifically by the delta-theta power median (FFT). Apparently, the coefficient of correlation between EEG and CBF depends on the efficacy of the EEG analysis m e t h o d used to describe arousal. We think, therefore, that the EEG-CBF 'relationship' found in the rabbit is not of cortical origin.

15P 51. Alpha coma in central pontine m y e l i n o l y s i s . G.A. Kader, G.S. Ferriss and C.A. Garcia (New Orleans, La.) An interesting case of a 35-year-old alcoholic black male, who presented with confusion, progressive coma and bilateral pneumonia, is discussed. The patient required intubation and was assisted by a respirator for 13 days, with a persistent alpha-coma pattern present on the EEG. Autopsy findings of Wernicke's encephalopathy and central pontine myelinolysis were present, without evidence of anoxic cerebral changes. Neurophysiologic correlations are discussed, with emphasis on the following points: (1) first description of alpha coma in central pontine myelinolysis; (2) persistent alpha-like activity in comatose patients is secondary to one of two mechanisms: cortical neuronal damage or thalamic release from mesencephalic and pontine projections; (3) reactivity of persistent alpha-like activity in comatose patients is dependent on an intact dorsomedian nucleus (at least unilaterally) and its cortical receiving neurons.

52. Hypersomnia with simultaneous waking and sleep EEG patterns mixed with bilateral spikes. -- E.

Niedermeyer, H.S. Singer, S.E. Folstein, R.P. Allen, F. Miranda, F. Fineyre and B.L. Bird (Baltimore, Md.) An 11-year-old boy had a 2 year history of marked hypersomnia. He was also dyslexic and used to he hyperkinetic (prior to onset of hypersomnia). He had no neurological deficit and never had epileptic seizures. Repeated EEG studies and power spectral analysis showed (a) short periods of typical waking activity with normal posterior alpha-rhythm, (b) prolonged periods of simultaneous posterior alpha-rhythm, spindles (vertex, fronto-central) and K complexes while behaviorally awake, and (c) prolonged periods of stage 2 or 3 sleep with spindles and abundant K complexes. Bilateral-synchronous spikes and spike-waves were common over anterior areas (slightly more prominent on the right) while the patient was electrically or behaviorally asleep. A 24 h polysomnogram confirmed excessive sleep duration at night and during the day (especially morning hours). A large REM sleep percentage was demonstrated on EMG and EOG basis but the concomitant EEG was dominated by high voltage slow activity with K complexe,% spindles as well as spikes and failed to show desynchronization. A neurotransmitter disturbance is presumed; possibly a state of 'hyperserotonergia' encroaching (and imposing slow sleep patterns) on both REM sleep and wakefulness. The linkage between sleep (or arousal) mechanisms and bilateral-synchronous spikes deserves special epileptological interest.