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Clinical observations on photosensitive epilepsy
FREE COMMUNICATIONS IN EEG It has been found in a group of 74 epileptic children during spontaneously or Nembutal induced sleep that excluding those showing focal or central discharges, 20 produced paroxysmal bursts on light pinprick stimulation of the limbs. There were two main types of bursts: bifrontal discharges at 5-7 c/see sometimes preceded by a short burst of fast waves and more generalized discharges in the delta range. The stimulus response delay varied between 0.5 and 2.0 sec. In all the recordings auditory and visual stimuli were given but in only 3 records was an auditory stimulus capable of producing a long lasting paroxysmal discharge. Two further cases produced similar discharges from photic stimulation during sleep. The discharges evoked by photic and auditory stimuli did not resemble those produced by the painful stimuli, Le., frontal theta discharges which were very similar from case to case and appeared to be specific for this type of stimulation. The occurrence of the bursts is paradoxical since one would expect a painful stimulus to awaken the patient or at least lighten the level of sleep as occurs in non-epileptics. Instead of the expected desynchronization through the ascending alerting system, the evoked theta bursts resemble synchronization of thalamic origin or even 14 and 6/sec positive spikes. This fact i s even more evident when the centrencephalic delta waves are evoked. This unusual response from epileptics does not appear to be due to dampening of the reticular system by the narcotic since K complex and other stages of sleep appear normally. These nociceptive bursts have not been found in sleep recordings of non-epileptics.
81. Clinical observations on photosensitive epilepsy.-H. Gerken (Kiel, West Germany). Follow-up studies were undertaken on 195 photosensitive children. Of these, 168 were suffering from cerebral seizures and the remaining 27 from a variety of other disorders including headache. Only four patients had sporadic photogenic seizures; the remainder had seizures unrelated to photic stimuli. The clinical picture of photosensitive epilepsy is very varied and includes almost all types of seizure patterns and of illness course. In the group studied febrile and afebrile grand-mal seizures were seen the most frequently, with focal seizures and pet~'t-mal next in frequency. Photosensitivity appears dominantly in females. The course is often very unfavorable especially in cases with focal symptoms and onset after the fifth year of life. Two-thirds of the cases studied started their disease before the sixth year of life, £e., before the age of maximal penetration of a genetically determined photosensitivity. In-
683
quiries into the family histories support the suggestion that there are additional genetic factors, independent from photosensitivity, which are of importance for the manifestation of epilepsy in carriers. Photosensitivity is regarded a s a symptom of a dysfunction of the reticulo-cortical system and this must already exist at a time when the characteristic photoconvulsive response has not yet appeared. It seems that the reticulo-cortical dysfunction is not linked to age but only to its sensitivity to stimulation by the optic path afferents.
82.
A mathematical model providing a synthesis between evoked and spontaneous phenomena of the E E G . - P . B, C. Fenwick and J. Dollimore (London, G.B.). Saunders showed the alpha rhythm to have a Gaussian distribution and to be generated by noise passed through a narrow band filter. McCullough et al. have suggested that the CNS is a state determined system. In collaboration with G. W. Fenton these two ideas have been combined by using the auto-regressive model. A model is calculated by fitting it to a length of EEG signal and then various properties of the models are investigated. If random noise is passed through a model, a wave form similar to the original EEG is generated b y the model. The model can be transformed into its impulse response and this shows many features which closely approximate to the average evoked potential. It is suggested that evoked phenomena may be better considered by more refined statistical techniques rather than simple measuring of latencies and so on. 83. Strychnine effects on cell membrane properties.-M. R. Klee and W. Heiss (Buffalo, N.Y., U.S.A.). Decreases in membrane potential, membrane resistance and amplitude of hyperpolarizing afterpotentials are caused in identified neurons of Aplysia Californica by adding 0.02-0.2% strychnine sulfate to the bathing solution. Most of those cells showing spontaneous discharges resulting from both endogeneous and synaptically induced activity started with depolarizing afterpotentials which increased in amplitude and caused bursts of spikes which were independent from the synaptic input (persistent after ligature of the axon of these unipolar cells). The nature of the repetitive activity and the sequence of depolarizing waves followed by hyperpolarizations are similar to phenomena seen in cortical and spinal neurons of mammals during strychnine seizure. Reducing the external calcium concentration or addition of cobalt to the strychninized medium caused mere-
81. Clinical observations on photosensitive epilepsy.-H. Gerken (Kiel, West Germany). Follow-up studies were undertaken on 195 photosensitive children. Of these, 168 were suffering from cerebral seizures and the remaining 27 from a variety of other disorders including headache. Only four patients had sporadic photogenic seizures; the remainder had seizures unrelated to photic stimuli. The clinical picture of photosensitive epilepsy is very varied and includes almost all types of seizure patterns and of illness course. In the group studied febrile and afebrile grand-mal seizures were seen the most frequently, with focal seizures and pet~'t-mal next in frequency. Photosensitivity appears dominantly in females. The course is often very unfavorable especially in cases with focal symptoms and onset after the fifth year of life. Two-thirds of the cases studied started their disease before the sixth year of life, £e., before the age of maximal penetration of a genetically determined photosensitivity. In-
683
quiries into the family histories support the suggestion that there are additional genetic factors, independent from photosensitivity, which are of importance for the manifestation of epilepsy in carriers. Photosensitivity is regarded a s a symptom of a dysfunction of the reticulo-cortical system and this must already exist at a time when the characteristic photoconvulsive response has not yet appeared. It seems that the reticulo-cortical dysfunction is not linked to age but only to its sensitivity to stimulation by the optic path afferents.
82.
A mathematical model providing a synthesis between evoked and spontaneous phenomena of the E E G . - P . B, C. Fenwick and J. Dollimore (London, G.B.). Saunders showed the alpha rhythm to have a Gaussian distribution and to be generated by noise passed through a narrow band filter. McCullough et al. have suggested that the CNS is a state determined system. In collaboration with G. W. Fenton these two ideas have been combined by using the auto-regressive model. A model is calculated by fitting it to a length of EEG signal and then various properties of the models are investigated. If random noise is passed through a model, a wave form similar to the original EEG is generated b y the model. The model can be transformed into its impulse response and this shows many features which closely approximate to the average evoked potential. It is suggested that evoked phenomena may be better considered by more refined statistical techniques rather than simple measuring of latencies and so on. 83. Strychnine effects on cell membrane properties.-M. R. Klee and W. Heiss (Buffalo, N.Y., U.S.A.). Decreases in membrane potential, membrane resistance and amplitude of hyperpolarizing afterpotentials are caused in identified neurons of Aplysia Californica by adding 0.02-0.2% strychnine sulfate to the bathing solution. Most of those cells showing spontaneous discharges resulting from both endogeneous and synaptically induced activity started with depolarizing afterpotentials which increased in amplitude and caused bursts of spikes which were independent from the synaptic input (persistent after ligature of the axon of these unipolar cells). The nature of the repetitive activity and the sequence of depolarizing waves followed by hyperpolarizations are similar to phenomena seen in cortical and spinal neurons of mammals during strychnine seizure. Reducing the external calcium concentration or addition of cobalt to the strychninized medium caused mere-