Formal aspects of vigilance during petit mal paroxysm.

Relationship between amplitude and interval of healthy and epileptic children's alpha activity was investigated. A directly proportional, though non-linear (mostly exponential) correlation was found, i. e. the higher the waves, the wider their are, and vice versa, the lower, the narrower. This is a well-known feature of clinical electroencephalography, representing a good organization of EEG elements and, in terms of physiology, suggesting good "co-operation" of the recruitment process excitation and inhibition. Low interval values are matched by equally low amplitude values while inhibition is adequate. At higher interval values, amplitude is seen rising rapidly, inhibition is inadequate resulting in "paroxysmal" alpha activity which is occasionally found assuming the nature of spike and slow wave activity. The appearance of such principal changes in the recruitment process is abrupt, but a certain part of the changes often fails to manifest itself in the EEG curve. Epileptic children's alpha activity has a relatively higher amplitude, slower rhythm and a more regular regulation of amplitudes and intervals as well as that of their ratio. This is in line with the tendency toward hypersynchrony of EEG elements in epileptics. Epileptic spike and wave activity has an opposite sense of regulation as to the relationship of spike amplitudes and intervals, the principle being: the higher the spikes, the shorter the intervals between them. Apart from frequency, amplitude and angular velocity, that is another substantial difference between alpha activity physiological synchronization in vigilance and pathological spike hypersynchronization in petit mal seizure. Changes in vigilance seem to be in agreement with this phenomenon. The nature of recruitment process regulation (given in type of function) appears to be very stable, often remaining unchanged even under pathological conditions. Thus e. g. aplha wave recruitment during vigilance and spike recruitment during seizure are linear in either case. But while in alpha activity the amplitude-interval ratio is directly proportional, in spikes the proportionality is inverse. Alpha activity appears to be accompanied by inhibitory processes, spikes by excitatory processes. The number of active neurones and their synchronization in the course of spike-wave episodes is higher than during alpha activity. For that reason, in the course of epileptic recruitment process, expedient temporal-spatial integration of neuronal activity decreases to be superceded by simplified hypersynchronous reverberation with lower analytical-synthetic ability and lower reflectivity.