Neurophysiological studies on atypical parkinsonian syndromes.

There have been a relatively large number of experimental investigations using neurophysiological techniques in patients with atypical parkinsonian syndromes (APs), including progressive supranuclear palsy, cortico-basal syndrome and multiple system atrophy. Earlier studies focused on the startle, blink and trigemino-cervical reflexes and showed several brainstem abnormalities. Studies using transcranial magnetic stimulation have revealed a number of abnormalities in primary motor cortex and inter-hemispheric connectivity. More recent studies have highlighted the role of cerebellar dysfunction and have reported altered movement kinematics. Neurophysiological abnormalities in APs reflect degeneration or functional changes at multiple brain levels. In the majority of cases, APs share common abnormalities even though some neurophysiological changes differ among the various APs. Evidence of a correlation between neurophysiological abnormalities and clinical signs and symptoms in APs is limited. This paper provides an update on the results of experimental investigations using neurophysiological techniques in APs and also reviews similarities and differences between APs and Parkinson's disease. The potential role of neurophysiological abnormalities in the clinical context of APs is also discussed.