Silent period in patients with parkinsonian rigidity

Abstract

When a muscle is unloaded suddenly during voluntary contraction, there is normally a break in the steady background of action potentials. This silent period is believed to result from a pause in spindle afferent discharge. In 4 patients with Parkinsonian rigidity, the silent period was demonstrated repeatedly by the unloading technique. In a patient with Parkinsonism and senile dementia, electrical silence was seen on 2 out of 17 trials. The appearance, latency, and duration of the silent period were similar to those found in normal subjects. The results were believed to show that, in these patients, the muscle spindles were normally sensitive to small changes of length during voluntary contraction. A loss of spindle sensitivity does not appear to be an essential com-ponent of Parkinsonian rigidity.