Neurophysiology of positive and negative myoclonus

Myoclonus is defined as a sudden, brief, jerky, shock-like, involuntary movement, arising from the central nervous system that can be caused by a muscular contraction, i.e. positive myoclonus, or by an interruption of muscular activity, i.e. negative myoclonus. Myoclonus can characterize a variety of neurological disorders, and often both positive and negative myoclonus can coexist. In this paper, we outline some relevant clinical aspects and neurophysiological features of the different types of myoclonus, with particular emphasis on the physiological findings. Indeed, since most myoclonus depend on enhancement of neuronal activities which are inherently present in normal subjects, electrophysiological studies are useful for elucidating the underlying pathophysiological mechanisms and for establishing the correct diagnosis. To reveal and discuss the peculiarities of soleus muscle in comparison with electrophysiological features of other leg muscles.