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The EEG society
534
Electroencephalography and Clinical Neurophysiology, 1976, 41:534--540 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
Society proceedings THE EEG SOCIETY London, January 17, 1976 Meetings Secretary : D.F. SCOTT The London Hospital, Whitechapel, London E. 1.1BB (Great Britain)
1. Infantile spasms and tuberous sclerosis syndrome (TSS). -- G. Pampiglione (London). One hundred children between 1957 and 1971 were found at follow-up to have developed 3 or more of the features of TSS; firstly, mental defect of varying severity (88%); secondly, seizures of various kinds, in addition to, or after the cessation of, bouts of massive spasms (75%); thirdly, fibroangioma of the face, often called adenoma sebaceum (77%); fourthly, non-pigmented areas of the skin (77%); and fifthly, miscellaneous (67%). In 69% of the children the syndrome of infantile spasms w a s present. The EEG abnormalities showed a great deal of individual variation but tended to be marked in the first 2 years of life. Their subsequent evolution was towards multifocal spikes mixed with irregular slow components, while there were usually some areas of relatively better preserved rhythmic activity. In older children the discharges disappeared altogether or the abnormalities became minimal with patchy excesses of intermediate slow activity. Careful examination of the skin for non-pigmented areas revealed that these were present in nearly half the total number of children in the first year of life and that the fibroangiomata of the face were occasionally recognizable in the first year, though more obvious after 4 years of age. Both clinical and EEG features were usually favourably modified by treatment with ACTH, irrespective of the final individual outcome and of the evolution o f the skin lesions.
2. A clinico~electroencephalographic study of neonatal EEG, using " b l i n d " inter-rater a s s e s s m e n t . - M.A. Pollack and D.F. Scott (New York, London). Few studies on the neonatal EEG have employed assessment of the main phenomena w i t h o u t reference to the age of the baby or other clinical information. The present investigation therefore n o t only involved the rating of the records w i t h o u t reference to these, but in addition two raters worked independently using a pro-forma which allowed semi-quantitative assessment of the phenomena seen. A group of 30 EEGs, 1 per patient, from consecutive neonates with a great variety of pathological disorders, especially perinatal asphyxia, were studied. All but 2 were taken within 4 weeks of birth. The ratings were compared with the clinical outcome as assessed by the paediatricians. Follow-up has so far been obtained on 27 of the 30 patients for an average of 10 months (range 3--18 months), and only the EEGs from patients with followup information will be considered. Of the 18 who showed a discontinuous EEG pattern 8 died, 10 survived, though only 5 were normal at follow-up. Seizure discharges observed in 11 were generally associated with a poor outcome. In contrast, those 9 who showed continuous activity did better, with 7 devoid of clinically discernible abnormality at follow-up. Though sharp waves and other transients occurred in all records, they tended to be scanty in those with a good outcome and
THE EEG SOCIETY were copious in those with a poor prognosis. This study suggests that a semi-quantitative approach to EEGs from the neonate can reveal information a b o u t o u t c o m e when details of age and level of arousal are not used.
3. The paradoxical lateralization of the scalprecorded visual evoked response. -- G. Barrett, L. Blumhardt, A.M. Halliday, E. Halliday and A. Kriss (London). Although the cortical representation of the left half of the visual field is in the right hemisphere and vice versa, the occipital response to a 2/sec reversing checkerboard pattern, presented in one half field, 0--16 ° , and recorded with respect to a mid-frontal reference, has a major positive c o m p o n e n t which appears at the midline and ipsilateral scalp electrodes, and not contralaterally. This definite finding has been seen in all healthy subjects tested. Because of the widespread distribution of the ipsilateral response, the voltage gradient is at its steepest between the midline electrode and any contralateral electrode. Hence, with a transverse bipolar chain of electrodes the maximal response is recorded over the contralateral hemisphere, although it is, in fact, maximal ipsilaterally. This unexpected result appears to be due to the fact that the visual cortical generator areas are situated largely on the medial and posteromedial surface of the hemispheres where the neurones are transversely oriented. The ipsilateral scalp electrodes are optimally placed to "view" the cortical surface of these neurones on the opposite hemisphere, whereas the contralateral electrodes lie more nearly perpendicular to the long axis of the dipoles. These results have important implications for the interpretation of evoked response asymmetries in field defects, which are broadly consistent with the findings in healthy subjects. The observations emphasize again the importance of the choice of montage in evoked response studies.
535 4. Vitamin B~ 2 deficiency and chronic cyanide toxicity in baboons. An EEG and neuropathological s t u d y . - R. Harris and W.T. Smith (London, Birmingham). Serial EEGs were obtained under anaesthesia in the course of a 4 year dietary experiment to study the effect of vitamin B~2 deficiency and chronic cyanide toxicity in 36 male, juvenile to pre-pubital baboons, who were divided into control and experimental sub-groups. The EEG effects of the anaesthesia have been described (Harris, "Electroenceph. clin. Neurophysiol.", 1972, 32: 81). At least 5 records were obtained from each baboon and the EEG assessments and final neuropathological examinations were made without knowledge of the experimental grouping. The biochemical state was monitored for each EEG. There were EEG changes which were probably due to maturation in the majority of the baboons. Abnormalities appeared in 7 baboons and became more severe in another whose records had shown generalized and focal spike discharges from the start. These were all BI~ deficient animals (with and without cyanide toxicity) and, in 2 of them, prolonged episodes of status epilepticus occurred after premedication with phencyclidine hydrochloride. A total of 10 animals developed problems during anaesthesia and only 2 were in the control group. No lesions which could be attributed to B~2 deficiency or cyanide intoxication were found in the brains, nor were there any changes which could be related to the seizures or EEG abnormalities. It is suggested that the EEG abnormalities were due to, or increased by, the induced biochemical disorder and together with the seizures, were further facilitated in the vulnerable baboons by the m e t h o d o f anaesthesia. 5. The use o f the EEG as a guide to the likelihood o f the occurrence o f epileptic attacks in neurosurgical p a t i e n t s . - R. Cabral and D.F. Scott (London). A systematic and detailed investigation was carried o u t on 199 EEGs from 83 patients
536 who underwent surgery for intracranial aneurysm or acoustic neuroma. The majority were investigated retrospectively but in about one half of those studied prospectively the effects of regular prophylactic anticonvulsant medication was also evaluated. The EEG criteria which separated a group of patients who developed epilepsy, from cases without fits, were subsequently obtained, Generally, the results indicated that the amounts of slow waves, spikes and sharp components at the site of the operative brain lesion were substantially and often significantly greater in EEGs from patients who developed post-operative epilepsy than in those cases without fits. In particular, it was found that patients who developed seizures exhibited "critical" amounts of slow activity and sharp waves and spikes. For example, in the majority of patients who underwent surgery for middle cerebral artery aneurysm or acoustic neuroma the lower limits for sharp waves and spikes, associated with the onset of fits, were respectively 50 and 10 per 100 sec epoch of the EEG. Finally, patients on prophylactic anticonvulsants exhibited substantially fewer "epileptic abnormalities" than did those patients who developed seizures. Further prospective studies to complement the present findings would seem to be warranted.
6. Television epilepsy and pattern sensitivity. --C.D. Binnie, C.E. Darby, A.T. Hindtey, A. Marlton, S,B. Stefansson and A. Wilkins (Wickford, ~ t h e n d , Cambridge). In early studies of television epilepsy, experimental viewing failed to elicit paroxysmal activity (Gastaut et al. "Epilepsia (Amst.)", I962, 7: 85), or did so only when the set was malfunctioning. This appears to conflict with clinical observations of seizures induced by correctly adjusted TV and with reports by Binnie et al. ("Brit. reed. J.", I973, 4: 378) and others, that normal TV can induce discharges in the EEGs of flicker-sensitive subjects. Further experience of 74 photosensitive patients (32 with TV epilepsy) confirmed our
SOCIETY PROCEEDINGS findings, as paroxysmal activity was elicited or increased by TV without gross malfunction in over 70%. Television should not normally flicker below 50 c/sec, yet can induce paroxysmal activity in subjects sensitive only to lower frequencies. This paradox, and the discrepancies between the negative results of Gastaut et al. (using studio equipment} and our findings (with domestic TVs in an area of indifferent reception} may be explained by the hypothesis that TV epilepsy can be induced by minor malfunction, notably line-jitter. Twenty-eight flicker-sensitive patients have viewed static or moving patterns of stripes or chequers, and TV correctly adjusted or with artificial line-jitter. Ten were sensitive to static patterns; 7 of these and 7 others exhibited discharges when the patterns were vibrated, simulating jitter. These 17 of 28 subjects were pattern-sensitive and all of these 17 were also sensitive to TV, whereas 4 of the 11 others were not. The association of pattern and TV sensitivities was significant by Fischer's exact probability test (P > 0.02).
7. The Royal Free Hospital EEG computer system. -- B.B. MacGillivray, D.G. Wadbrook and J. Price (London). The project has been set up to compute
automated reports from routine clinical EEG records, the motivation being to establish objective diagnostic criteria by quantification. The final m a c h i n e - g e n e r a ~ report consists of a description in the form of a diagrammatic statement of the presence of abnormalities, both continuous and paroxysmal (the factual report) and a diagnostic statement which indicated the nature and distribution of the abnormalities found, and is derived via a logical process from these:measurements. Sixteen EEG channels are digitized and stored o n magnetic: tape for subsequent retrieval. Data reduction is achieved by dividing the record into stationary and paroxysmal periods, using a series of short epoch (1 sec)
THE EEG SOCIETY Fourier Transforms to obtain broadband spectral estimates. A set of decision trees combines the o u t p u t of the data reduction and feature detection processes to give the final diagnostic statement. The inclusion of clinical data will provide the appropriate clinical relevance but is n o t y e t implemented. The system is written in FORTRAN and is designed to operate on a small disc-based computer system. 8. H reflex modulation by natural stimulation o f the s k i n . - M.A. Sabbahi Awadalla and E.M. Sedgwick (Southampton). The size of an H reflex (Hoffman) is a measure of the accessibility of, motorneurones to a synchronous low threshold monosynaptic afferent stimulus. Using the H reflex the effect o f conditioning stimuli on m o t o r neurone excitability can be meaured. We have used this technique to study changes in soleus monosynaptic reflex excitability following natural skin stimuli. The stimuli used were mechano-receptor activation by a scrubbing brush and cooling the skin by a pain relieving spray. The test H reflex was evoked every 3--5 sec with a stimulus strength adjusted to give a submaximal H reflex with no M response. The results show that the H reflex is decreased by 20--50% during either type of stimulation and t h a t the receptive skin area includes the sole of the foot and the skin of the calf. Lesser depression followed cooling of areas distant from the muscle, but no contralateral effects were seen. Maximal effects followed stimulation of the sole of the foot. Human nociceptive reflexes have been studied by Hagbarth (1960) but our stimuli are n o t noxious and their effects are different. We suggest that non-noxious stimuli normally modulate the excitability of motorneurones in a subtle and complex way.
9. A microprocessor-based semi-automatic instrument to measure motor nerve conduction velocity. -- Z. TSrSk (Stevenage).
537 The instrument was designed to be suitable for making large numbers of measurements of the conduction velocity of the fastest m o t o r fibres (max MNCV) of peripheral nerves by non-specialist users. It is m o u n t e d in a standard 19 X 9 in. cabinet, is wholly battery-powered and, instead of an analogue display, has a digital readout directly in m/sec. An 8-bit microprocessor (Intel 8008) is equipped with programmable read-only m e m o r y elements providing storage for 256 8-bit words. An almost 10-fold extension of this capacity is provided for in the design. After checking the electrode impedances, a 50 V stimulus is delivered to the distal stimulating site and increased until, by a criterion of increasing slope of the response, the stimulus is found to be supramaximal. Four measurements of the latency are taken at this stimulus level and averaged. Then the sequence is repeated at the proximal stimulating site. The user has to set the distance between the two on a dial; this is read, the arithmetic performed and the max MNCV displayed as two digits on conventional 7-segment LED units. The versatility offered by this design is n o t as y e t fully explored. 10. Preliminary assessment o f a semi-automatic conduction velocity m e t e r . - S.G. Baylis and J. Rossetti (Guildford). The semi-automatic conduction velocity meter described above (Abstract 9) was used to measure the m o t o r conduction velocity in the inedian nerve of the forearm of fit young adults. The measurements were repeated using conventional EMG techniques. The mean velocity and standard deviation by the semi-automatic method were 56.76 +- 3.92 m/sec and by conventional methods 58.43 + 3.98 and 5 7 . 9 8 + 3.85 m/sec respectively for two independent operators. Sources of error noted during the study were confined to incorrect positioning of the recording electrode, which gave an erroneous slow velocity, and to working in a very large 50 c/sec field, which would n o t
538 occur in the clinical situation. Other operator errors such as high electrode resistance are checked for, and indicated by the machine, which will n o t proceed with measurement until they are corrected. As an index o~ repeatability of measurements made by t h e semi-automatic machine, the median nerve m o t o r conduction velocity of 2 subjects was repeatedly measured by a group of electrophysiologically unskilled operators who had received only a short period of instruction. Velocity and standard deviations were 55.7 -+ 2.93 and 59.4 -+ 2.95 m/sec, suggesting that the semi-automatic machine is capable of reasonably accurate measurement in unskilled hands and is suitable for screening procedures.
11. Motor nerve conduction velocity before and after haemodialysis. -- Z. TSrSk (Stevenage). The conduction velocity of the fastest motor fibres of the median nerve (max MNCB) was measured in 12 patients immediately before and after haemodialysis lasting an average of 6 h. An automatic purpose-made instrument was used (Abstract 9). The patients were on a 3/week dialysis schedule. The pre
12. A preliminary pharmacological analysis of
SOCIETY PROCEEDINGS
the contingent negative variation (CNV). -J.W. Thompson, P. Newton, P.V. Pocock, R. Cooper, H. Crow, W.C. McCallum and D. Papakostopoulos (Newcastle upon Tyne, Bristol).
The CNV (Walter et al., "Nature (Lond.)", 1964, 203: 380) is known to be modified by drugs (Ashton et al., "Electroenceph. clin. Neurophysiol.", 1974, 37: 59). Nevertheless, drugs do not seem to have been used to analyse the ~europharmacological mechanisms subserving the CNV. In the present placebo-controlled study, three drugs known to act as competitive antagonists to likely central neurotransmitters, namely, atropine (acetylcholine), metoclopramide (dopamine) and t h y m o x a m i n e {noradrenalin, an adrenoceptor blocker) were studied. Twelve normal subjects t o o k part in sixteen experiments in which a single-blind and pseudo-random design was used. They received one drug per experiment. Records were made from ten scalp electrodes (nasion, L and R frontal, L and R central, Cz, L and R parietal, with linked mastoids as a c o m m o n reference). EOG, EMG, ECG, GSR, finger-tip temperature, respiration and intermittent blood pressure were also monitored. After recording control responses of AERs, CNVs and P300 waves, the drug was rejected i.m. and the responses repeated. CNV magnitude was depressed after atropine (0.4--0.5 mg) and metoclopramide (5--7 mg).
13. Evoked and intrinsic activities in the cerebellum o f conscious man. -- D. Papakostopoulos, R. Cooper, B. Cummins and A. Winter (Bristol). Multi-channel records of the evoked potentials (EPs) and the intrinsic activity have been obtained from the anterior cerebellar cortex in a patient carrying 27 gold electrodes that were implanted for treatment. Auditory stimulation did not produce reli-
THE EEG SOCIETY able potential changes. The somatosensory EPs to left median nerve stimulation at the elbow started with a negative deflection and a delay of 13 msec. They were ipsi-and contralaterally distributed with some variability in waveform from area to area. Visual EPs to flash started with a positive deflection which had a latency of 34 msec. They, too, had variable wave form from area to area and were bilaterally distributed. Intrinsic activity having frequencies of 50--110 c/sec were observed. These frequencies were more pronounced at the medial parts of the cerebellar cortex; they had great variability and were uncorrelated with rhythms of similar frequency from adjacent areas. The lower frequencies, in particular those between 8 and 12 c/sec, were significantly more abundant in lateral areas, and presented a high degree of correlation in the medio-lateral direction. The data indicate spatial specificity in the human cerebellar cortex and an organization of the slow frequencies following the direction of the cerebellar folia. The possibility of extracerebellar pacemakers for the slow rhythms and intraCortical circuits for the faster rhythms is also suggested. 14. Chronic cerebellar stimulation in the treatm e n t of generalized epilepsy: a case report. -- G.S. Brindley, M.A. Falconer, G.W. Fenton, P.B.C. Fenwick, C.E. Polkey and D. Rushton (London). The patient, a 29-year-old girl of dull intelligence (WAIS full scale I.Q. 80) and immature dependent personality had had intractable epilepsy since the age of 12 years, with generalized convulsions, transient drop attacks, and brief petit mal seizures. The average frequency was 53 drop attacks, 57 petit mal attacks every month, and one grand mal seizure every 2 months. EEG recording showed generalized spike and wave complexes with independent right and left posterior and mid-temporal focal spike discharges, most marked in the left posterior temporal region. A cerebellar implant was inserted and chronic stimulation has
539 been performed, using Cooper's technique, for just over 10 months. Seizure frequency n o w averages 15 drop attacks and 57 petit mal attacks each month, with 3 major attacks only. The patient is much brighter, more alert and confident in her social relationships. Drop attacks are less abrupt in onset. Psychometric testing, though showing no I.Q. change, indicates improvement in performance on tests of verbal and visual learning. Anticonvulsant medication continued unchanged throughout. 15. Immediate effects of cerebellar stimulation in an epileptic p a t i e n t . - G.S. Brindley, M.A. Falconer, G.W. Fenton, P.B.C. Fenwick, C.E. Polkey and D. Rushton (London). Unilateral electrical stimulation of the cerebellar cortex (Abstract 14) with ten 1-msec pulses/sec of strength (usually 5--10 mA) near the threshold for causing headache had no effect, ipsilaterally or contralaterally, on limbmuscle tone, tendon reflexes, gait, speed or accuracy of rapid repetitive movement, latency of hand movement in response to a visual signal or long-latency stretch reflex in the thumb. Handwriting (right hand) was also unaffected. No nystagmus was caused, other than that clearly attributable to cranial nerve stimulation, and the normal nystagmus on extreme deviation of the eyes was unaffected. When stimulation caused no headache or cranial nerve effects, the patient was unaware of it. Effects apparently due to spread of current to the ipsilateral Vth, VIth or VIIth nerves or nuclei could be elicited from 7 of the 8 electrode sets; thresholds for these ranged from 3 to 15 mA. 16. Scalp evoked responses to cerebellar stimulation in man. -- G.S. Brindley, M.A. Falconer, G.W. Fenton, P.B.C. Fenwick, C.E. Polkey and D. Rushton (London). Averaged scalp evoked responses to electrical stimulation of the cerebellum were recorded in a patient who has cerebellar stimu-
540
l a t i n g electrodes implanted for intractable epilepsy (Abstract 14). Stimuli were delivered to the cerebellum at 3/sec and responses were recorded over the contralateral sensorimotor area, through electrodes arranged to minimize the stimulus artefact. They were of 40--45 msec latency. The strength of cerebellar stimulation required was only a little below the range in which facial paraesthesiae occurred, and the size of the evoked potential increased rapidly in this range of stimulus strength, al-
SOCIETY PROCEEDINGS
though remaining of the same latency and general form. There were no evoked potentials between 5 and 40 msec latency, but any o f less than about 5 msec latency would have been obscured by stimulus artefact. We concluded that the response may have been evoked by weak stimulation of the trigeminat nerve root and gave, in this patient, no unequivocal evidence of a functional cerebeUar output.
Electroencephalography and Clinical Neurophysiology, 1976, 41:534--540 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
Society proceedings THE EEG SOCIETY London, January 17, 1976 Meetings Secretary : D.F. SCOTT The London Hospital, Whitechapel, London E. 1.1BB (Great Britain)
1. Infantile spasms and tuberous sclerosis syndrome (TSS). -- G. Pampiglione (London). One hundred children between 1957 and 1971 were found at follow-up to have developed 3 or more of the features of TSS; firstly, mental defect of varying severity (88%); secondly, seizures of various kinds, in addition to, or after the cessation of, bouts of massive spasms (75%); thirdly, fibroangioma of the face, often called adenoma sebaceum (77%); fourthly, non-pigmented areas of the skin (77%); and fifthly, miscellaneous (67%). In 69% of the children the syndrome of infantile spasms w a s present. The EEG abnormalities showed a great deal of individual variation but tended to be marked in the first 2 years of life. Their subsequent evolution was towards multifocal spikes mixed with irregular slow components, while there were usually some areas of relatively better preserved rhythmic activity. In older children the discharges disappeared altogether or the abnormalities became minimal with patchy excesses of intermediate slow activity. Careful examination of the skin for non-pigmented areas revealed that these were present in nearly half the total number of children in the first year of life and that the fibroangiomata of the face were occasionally recognizable in the first year, though more obvious after 4 years of age. Both clinical and EEG features were usually favourably modified by treatment with ACTH, irrespective of the final individual outcome and of the evolution o f the skin lesions.
2. A clinico~electroencephalographic study of neonatal EEG, using " b l i n d " inter-rater a s s e s s m e n t . - M.A. Pollack and D.F. Scott (New York, London). Few studies on the neonatal EEG have employed assessment of the main phenomena w i t h o u t reference to the age of the baby or other clinical information. The present investigation therefore n o t only involved the rating of the records w i t h o u t reference to these, but in addition two raters worked independently using a pro-forma which allowed semi-quantitative assessment of the phenomena seen. A group of 30 EEGs, 1 per patient, from consecutive neonates with a great variety of pathological disorders, especially perinatal asphyxia, were studied. All but 2 were taken within 4 weeks of birth. The ratings were compared with the clinical outcome as assessed by the paediatricians. Follow-up has so far been obtained on 27 of the 30 patients for an average of 10 months (range 3--18 months), and only the EEGs from patients with followup information will be considered. Of the 18 who showed a discontinuous EEG pattern 8 died, 10 survived, though only 5 were normal at follow-up. Seizure discharges observed in 11 were generally associated with a poor outcome. In contrast, those 9 who showed continuous activity did better, with 7 devoid of clinically discernible abnormality at follow-up. Though sharp waves and other transients occurred in all records, they tended to be scanty in those with a good outcome and
THE EEG SOCIETY were copious in those with a poor prognosis. This study suggests that a semi-quantitative approach to EEGs from the neonate can reveal information a b o u t o u t c o m e when details of age and level of arousal are not used.
3. The paradoxical lateralization of the scalprecorded visual evoked response. -- G. Barrett, L. Blumhardt, A.M. Halliday, E. Halliday and A. Kriss (London). Although the cortical representation of the left half of the visual field is in the right hemisphere and vice versa, the occipital response to a 2/sec reversing checkerboard pattern, presented in one half field, 0--16 ° , and recorded with respect to a mid-frontal reference, has a major positive c o m p o n e n t which appears at the midline and ipsilateral scalp electrodes, and not contralaterally. This definite finding has been seen in all healthy subjects tested. Because of the widespread distribution of the ipsilateral response, the voltage gradient is at its steepest between the midline electrode and any contralateral electrode. Hence, with a transverse bipolar chain of electrodes the maximal response is recorded over the contralateral hemisphere, although it is, in fact, maximal ipsilaterally. This unexpected result appears to be due to the fact that the visual cortical generator areas are situated largely on the medial and posteromedial surface of the hemispheres where the neurones are transversely oriented. The ipsilateral scalp electrodes are optimally placed to "view" the cortical surface of these neurones on the opposite hemisphere, whereas the contralateral electrodes lie more nearly perpendicular to the long axis of the dipoles. These results have important implications for the interpretation of evoked response asymmetries in field defects, which are broadly consistent with the findings in healthy subjects. The observations emphasize again the importance of the choice of montage in evoked response studies.
535 4. Vitamin B~ 2 deficiency and chronic cyanide toxicity in baboons. An EEG and neuropathological s t u d y . - R. Harris and W.T. Smith (London, Birmingham). Serial EEGs were obtained under anaesthesia in the course of a 4 year dietary experiment to study the effect of vitamin B~2 deficiency and chronic cyanide toxicity in 36 male, juvenile to pre-pubital baboons, who were divided into control and experimental sub-groups. The EEG effects of the anaesthesia have been described (Harris, "Electroenceph. clin. Neurophysiol.", 1972, 32: 81). At least 5 records were obtained from each baboon and the EEG assessments and final neuropathological examinations were made without knowledge of the experimental grouping. The biochemical state was monitored for each EEG. There were EEG changes which were probably due to maturation in the majority of the baboons. Abnormalities appeared in 7 baboons and became more severe in another whose records had shown generalized and focal spike discharges from the start. These were all BI~ deficient animals (with and without cyanide toxicity) and, in 2 of them, prolonged episodes of status epilepticus occurred after premedication with phencyclidine hydrochloride. A total of 10 animals developed problems during anaesthesia and only 2 were in the control group. No lesions which could be attributed to B~2 deficiency or cyanide intoxication were found in the brains, nor were there any changes which could be related to the seizures or EEG abnormalities. It is suggested that the EEG abnormalities were due to, or increased by, the induced biochemical disorder and together with the seizures, were further facilitated in the vulnerable baboons by the m e t h o d o f anaesthesia. 5. The use o f the EEG as a guide to the likelihood o f the occurrence o f epileptic attacks in neurosurgical p a t i e n t s . - R. Cabral and D.F. Scott (London). A systematic and detailed investigation was carried o u t on 199 EEGs from 83 patients
536 who underwent surgery for intracranial aneurysm or acoustic neuroma. The majority were investigated retrospectively but in about one half of those studied prospectively the effects of regular prophylactic anticonvulsant medication was also evaluated. The EEG criteria which separated a group of patients who developed epilepsy, from cases without fits, were subsequently obtained, Generally, the results indicated that the amounts of slow waves, spikes and sharp components at the site of the operative brain lesion were substantially and often significantly greater in EEGs from patients who developed post-operative epilepsy than in those cases without fits. In particular, it was found that patients who developed seizures exhibited "critical" amounts of slow activity and sharp waves and spikes. For example, in the majority of patients who underwent surgery for middle cerebral artery aneurysm or acoustic neuroma the lower limits for sharp waves and spikes, associated with the onset of fits, were respectively 50 and 10 per 100 sec epoch of the EEG. Finally, patients on prophylactic anticonvulsants exhibited substantially fewer "epileptic abnormalities" than did those patients who developed seizures. Further prospective studies to complement the present findings would seem to be warranted.
6. Television epilepsy and pattern sensitivity. --C.D. Binnie, C.E. Darby, A.T. Hindtey, A. Marlton, S,B. Stefansson and A. Wilkins (Wickford, ~ t h e n d , Cambridge). In early studies of television epilepsy, experimental viewing failed to elicit paroxysmal activity (Gastaut et al. "Epilepsia (Amst.)", I962, 7: 85), or did so only when the set was malfunctioning. This appears to conflict with clinical observations of seizures induced by correctly adjusted TV and with reports by Binnie et al. ("Brit. reed. J.", I973, 4: 378) and others, that normal TV can induce discharges in the EEGs of flicker-sensitive subjects. Further experience of 74 photosensitive patients (32 with TV epilepsy) confirmed our
SOCIETY PROCEEDINGS findings, as paroxysmal activity was elicited or increased by TV without gross malfunction in over 70%. Television should not normally flicker below 50 c/sec, yet can induce paroxysmal activity in subjects sensitive only to lower frequencies. This paradox, and the discrepancies between the negative results of Gastaut et al. (using studio equipment} and our findings (with domestic TVs in an area of indifferent reception} may be explained by the hypothesis that TV epilepsy can be induced by minor malfunction, notably line-jitter. Twenty-eight flicker-sensitive patients have viewed static or moving patterns of stripes or chequers, and TV correctly adjusted or with artificial line-jitter. Ten were sensitive to static patterns; 7 of these and 7 others exhibited discharges when the patterns were vibrated, simulating jitter. These 17 of 28 subjects were pattern-sensitive and all of these 17 were also sensitive to TV, whereas 4 of the 11 others were not. The association of pattern and TV sensitivities was significant by Fischer's exact probability test (P > 0.02).
7. The Royal Free Hospital EEG computer system. -- B.B. MacGillivray, D.G. Wadbrook and J. Price (London). The project has been set up to compute
automated reports from routine clinical EEG records, the motivation being to establish objective diagnostic criteria by quantification. The final m a c h i n e - g e n e r a ~ report consists of a description in the form of a diagrammatic statement of the presence of abnormalities, both continuous and paroxysmal (the factual report) and a diagnostic statement which indicated the nature and distribution of the abnormalities found, and is derived via a logical process from these:measurements. Sixteen EEG channels are digitized and stored o n magnetic: tape for subsequent retrieval. Data reduction is achieved by dividing the record into stationary and paroxysmal periods, using a series of short epoch (1 sec)
THE EEG SOCIETY Fourier Transforms to obtain broadband spectral estimates. A set of decision trees combines the o u t p u t of the data reduction and feature detection processes to give the final diagnostic statement. The inclusion of clinical data will provide the appropriate clinical relevance but is n o t y e t implemented. The system is written in FORTRAN and is designed to operate on a small disc-based computer system. 8. H reflex modulation by natural stimulation o f the s k i n . - M.A. Sabbahi Awadalla and E.M. Sedgwick (Southampton). The size of an H reflex (Hoffman) is a measure of the accessibility of, motorneurones to a synchronous low threshold monosynaptic afferent stimulus. Using the H reflex the effect o f conditioning stimuli on m o t o r neurone excitability can be meaured. We have used this technique to study changes in soleus monosynaptic reflex excitability following natural skin stimuli. The stimuli used were mechano-receptor activation by a scrubbing brush and cooling the skin by a pain relieving spray. The test H reflex was evoked every 3--5 sec with a stimulus strength adjusted to give a submaximal H reflex with no M response. The results show that the H reflex is decreased by 20--50% during either type of stimulation and t h a t the receptive skin area includes the sole of the foot and the skin of the calf. Lesser depression followed cooling of areas distant from the muscle, but no contralateral effects were seen. Maximal effects followed stimulation of the sole of the foot. Human nociceptive reflexes have been studied by Hagbarth (1960) but our stimuli are n o t noxious and their effects are different. We suggest that non-noxious stimuli normally modulate the excitability of motorneurones in a subtle and complex way.
9. A microprocessor-based semi-automatic instrument to measure motor nerve conduction velocity. -- Z. TSrSk (Stevenage).
537 The instrument was designed to be suitable for making large numbers of measurements of the conduction velocity of the fastest m o t o r fibres (max MNCV) of peripheral nerves by non-specialist users. It is m o u n t e d in a standard 19 X 9 in. cabinet, is wholly battery-powered and, instead of an analogue display, has a digital readout directly in m/sec. An 8-bit microprocessor (Intel 8008) is equipped with programmable read-only m e m o r y elements providing storage for 256 8-bit words. An almost 10-fold extension of this capacity is provided for in the design. After checking the electrode impedances, a 50 V stimulus is delivered to the distal stimulating site and increased until, by a criterion of increasing slope of the response, the stimulus is found to be supramaximal. Four measurements of the latency are taken at this stimulus level and averaged. Then the sequence is repeated at the proximal stimulating site. The user has to set the distance between the two on a dial; this is read, the arithmetic performed and the max MNCV displayed as two digits on conventional 7-segment LED units. The versatility offered by this design is n o t as y e t fully explored. 10. Preliminary assessment o f a semi-automatic conduction velocity m e t e r . - S.G. Baylis and J. Rossetti (Guildford). The semi-automatic conduction velocity meter described above (Abstract 9) was used to measure the m o t o r conduction velocity in the inedian nerve of the forearm of fit young adults. The measurements were repeated using conventional EMG techniques. The mean velocity and standard deviation by the semi-automatic method were 56.76 +- 3.92 m/sec and by conventional methods 58.43 + 3.98 and 5 7 . 9 8 + 3.85 m/sec respectively for two independent operators. Sources of error noted during the study were confined to incorrect positioning of the recording electrode, which gave an erroneous slow velocity, and to working in a very large 50 c/sec field, which would n o t
538 occur in the clinical situation. Other operator errors such as high electrode resistance are checked for, and indicated by the machine, which will n o t proceed with measurement until they are corrected. As an index o~ repeatability of measurements made by t h e semi-automatic machine, the median nerve m o t o r conduction velocity of 2 subjects was repeatedly measured by a group of electrophysiologically unskilled operators who had received only a short period of instruction. Velocity and standard deviations were 55.7 -+ 2.93 and 59.4 -+ 2.95 m/sec, suggesting that the semi-automatic machine is capable of reasonably accurate measurement in unskilled hands and is suitable for screening procedures.
11. Motor nerve conduction velocity before and after haemodialysis. -- Z. TSrSk (Stevenage). The conduction velocity of the fastest motor fibres of the median nerve (max MNCB) was measured in 12 patients immediately before and after haemodialysis lasting an average of 6 h. An automatic purpose-made instrument was used (Abstract 9). The patients were on a 3/week dialysis schedule. The pre
12. A preliminary pharmacological analysis of
SOCIETY PROCEEDINGS
the contingent negative variation (CNV). -J.W. Thompson, P. Newton, P.V. Pocock, R. Cooper, H. Crow, W.C. McCallum and D. Papakostopoulos (Newcastle upon Tyne, Bristol).
The CNV (Walter et al., "Nature (Lond.)", 1964, 203: 380) is known to be modified by drugs (Ashton et al., "Electroenceph. clin. Neurophysiol.", 1974, 37: 59). Nevertheless, drugs do not seem to have been used to analyse the ~europharmacological mechanisms subserving the CNV. In the present placebo-controlled study, three drugs known to act as competitive antagonists to likely central neurotransmitters, namely, atropine (acetylcholine), metoclopramide (dopamine) and t h y m o x a m i n e {noradrenalin, an adrenoceptor blocker) were studied. Twelve normal subjects t o o k part in sixteen experiments in which a single-blind and pseudo-random design was used. They received one drug per experiment. Records were made from ten scalp electrodes (nasion, L and R frontal, L and R central, Cz, L and R parietal, with linked mastoids as a c o m m o n reference). EOG, EMG, ECG, GSR, finger-tip temperature, respiration and intermittent blood pressure were also monitored. After recording control responses of AERs, CNVs and P300 waves, the drug was rejected i.m. and the responses repeated. CNV magnitude was depressed after atropine (0.4--0.5 mg) and metoclopramide (5--7 mg).
13. Evoked and intrinsic activities in the cerebellum o f conscious man. -- D. Papakostopoulos, R. Cooper, B. Cummins and A. Winter (Bristol). Multi-channel records of the evoked potentials (EPs) and the intrinsic activity have been obtained from the anterior cerebellar cortex in a patient carrying 27 gold electrodes that were implanted for treatment. Auditory stimulation did not produce reli-
THE EEG SOCIETY able potential changes. The somatosensory EPs to left median nerve stimulation at the elbow started with a negative deflection and a delay of 13 msec. They were ipsi-and contralaterally distributed with some variability in waveform from area to area. Visual EPs to flash started with a positive deflection which had a latency of 34 msec. They, too, had variable wave form from area to area and were bilaterally distributed. Intrinsic activity having frequencies of 50--110 c/sec were observed. These frequencies were more pronounced at the medial parts of the cerebellar cortex; they had great variability and were uncorrelated with rhythms of similar frequency from adjacent areas. The lower frequencies, in particular those between 8 and 12 c/sec, were significantly more abundant in lateral areas, and presented a high degree of correlation in the medio-lateral direction. The data indicate spatial specificity in the human cerebellar cortex and an organization of the slow frequencies following the direction of the cerebellar folia. The possibility of extracerebellar pacemakers for the slow rhythms and intraCortical circuits for the faster rhythms is also suggested. 14. Chronic cerebellar stimulation in the treatm e n t of generalized epilepsy: a case report. -- G.S. Brindley, M.A. Falconer, G.W. Fenton, P.B.C. Fenwick, C.E. Polkey and D. Rushton (London). The patient, a 29-year-old girl of dull intelligence (WAIS full scale I.Q. 80) and immature dependent personality had had intractable epilepsy since the age of 12 years, with generalized convulsions, transient drop attacks, and brief petit mal seizures. The average frequency was 53 drop attacks, 57 petit mal attacks every month, and one grand mal seizure every 2 months. EEG recording showed generalized spike and wave complexes with independent right and left posterior and mid-temporal focal spike discharges, most marked in the left posterior temporal region. A cerebellar implant was inserted and chronic stimulation has
539 been performed, using Cooper's technique, for just over 10 months. Seizure frequency n o w averages 15 drop attacks and 57 petit mal attacks each month, with 3 major attacks only. The patient is much brighter, more alert and confident in her social relationships. Drop attacks are less abrupt in onset. Psychometric testing, though showing no I.Q. change, indicates improvement in performance on tests of verbal and visual learning. Anticonvulsant medication continued unchanged throughout. 15. Immediate effects of cerebellar stimulation in an epileptic p a t i e n t . - G.S. Brindley, M.A. Falconer, G.W. Fenton, P.B.C. Fenwick, C.E. Polkey and D. Rushton (London). Unilateral electrical stimulation of the cerebellar cortex (Abstract 14) with ten 1-msec pulses/sec of strength (usually 5--10 mA) near the threshold for causing headache had no effect, ipsilaterally or contralaterally, on limbmuscle tone, tendon reflexes, gait, speed or accuracy of rapid repetitive movement, latency of hand movement in response to a visual signal or long-latency stretch reflex in the thumb. Handwriting (right hand) was also unaffected. No nystagmus was caused, other than that clearly attributable to cranial nerve stimulation, and the normal nystagmus on extreme deviation of the eyes was unaffected. When stimulation caused no headache or cranial nerve effects, the patient was unaware of it. Effects apparently due to spread of current to the ipsilateral Vth, VIth or VIIth nerves or nuclei could be elicited from 7 of the 8 electrode sets; thresholds for these ranged from 3 to 15 mA. 16. Scalp evoked responses to cerebellar stimulation in man. -- G.S. Brindley, M.A. Falconer, G.W. Fenton, P.B.C. Fenwick, C.E. Polkey and D. Rushton (London). Averaged scalp evoked responses to electrical stimulation of the cerebellum were recorded in a patient who has cerebellar stimu-
540
l a t i n g electrodes implanted for intractable epilepsy (Abstract 14). Stimuli were delivered to the cerebellum at 3/sec and responses were recorded over the contralateral sensorimotor area, through electrodes arranged to minimize the stimulus artefact. They were of 40--45 msec latency. The strength of cerebellar stimulation required was only a little below the range in which facial paraesthesiae occurred, and the size of the evoked potential increased rapidly in this range of stimulus strength, al-
SOCIETY PROCEEDINGS
though remaining of the same latency and general form. There were no evoked potentials between 5 and 40 msec latency, but any o f less than about 5 msec latency would have been obscured by stimulus artefact. We concluded that the response may have been evoked by weak stimulation of the trigeminat nerve root and gave, in this patient, no unequivocal evidence of a functional cerebeUar output.