(1) Epileptic myoclonus may persist, though decreasing, for the entire duration of sleep (Jacksonian epilepsy, epilepsia partialis continuans) or disappear in the lightest phases of sleep (degenerative myoclonic epilepsy, rhythmic myoclonus in the course of encephalitis). It is probable that the different sites of the lesion and/or the different nature (pyramidal-extra-pyramidal) of the myoclonus are responsible for this different evolution during sleep. (2) The oro-velo-palatal, the skeletal myoclonus and the opsoclonus disappear early during sleep behaving as other disorders of movements of extra-pyramidal origin (Parkinsonian tremor, choreo-athetoid movements, etc.). (3) Myoclonus of spinal cord origin and facial spasm persist unchanged for the entire duration of sleep, as do the fasciculations of amyotrophic lateral sclerosis.