Evolving ideas on the neurophysiology of myoclonus.

Early observations, made between 1935 and 1947, on the EEG discharges associated with myoclonic jerking are reviewed, together with the contemporary findings on the stimulus-sensitive myoclonus produced in cats under chloralose anesthesia. The accumulating evidence on the relative roles of cortex, brainstem, and cerebellum in producing this type of myoclonus is briefly summarized. The significance of large SEPs and their presence and absence in various clinical types of myoclonus is considered. Three distinctions are drawn with regard to the clinical features of myoclonic jerking: between action myoclonus and myoclonus at rest; between focal and generalized jerking; and between the lightning-like, irregular, stimulus-sensitive jerks of myoclonic epilepsy and the rhythmical, stimulus-insensitive jerking of segmental myoclonus. Some findings bearing on the possible mechanisms of the abnormal discharges responsible at cell membrane level are mentioned.