REGULATORY MECHANISMS IN PARKINSONIAN TREMOR

Abstract

With the purpose of showing that the amplitude of Parkinsonian tremor is not independent of peripheral influences and that dysfunction in "servo" mechanisms may have a role, 8 Parkinsonian patients were studied by means of electromyographs and ergographs. Concentric needle electrodes were inserted into the adductor of the right thumb and recordings were made of the "silent period", from the muscle following heavy infiltration with anesthesia and from the muscle following a modification of proprioceptive input. In patients with tremor and normal resting tone the damping system is functional except when tremor volleys are in progress. At this time the spindles are not susceptible to "unloading". Subjects experiencing rigidity and tremor show a defective response to twitches but in all, the silence following even the weakest tremor was striking. An injection of procaine into the muscle increased the tremor not only involving the adductor but also other muscles participating. It was also shown that central influences may control the frequency of tremor while peripheral influences determined the amplitude. The sensitivity of tremor, thus illustrated, clearly differentiates it from plastic rigidity, which does not respond in this manner and affirms the clinical impression that impulses producing tremor and rigidity in Parkinsonism may utilize anatomically distinct pathways.