Inhibition of the Muscle Spindle Discharge by Ventrolateral Thalamic Stimulation

Abstract

Introduction With the recent increasing success of stereotactic surgery of the thalamus in the treatment of Parkinsonism, renewed interest in the function of the ventrolateral nucleus of the thalamus has been awakened, Particularly with respect to its role in the Parkinsonian state. Previous hypotheses by one of us (A. A. W.)²⁵regarding the pathophysiology underlying the symptoms of Parkinsonism have not included any definition of the role played by either ventrolateral thalamic or pallidal circuit. In addition to postulated dysfunction of extrapyramidal circuits, altered peripheral and cord mechanisms have also been invoked in the attempt to explain rigidity, akinesia, and tremor. Byrnes³stated that lesions are present in the muscle spindle itself which are specific for postencephalitic Parkinson's disease. He described degeneration of the intrafusal nerve and eventual disintegration of the muscle spindle. However, there has been no confirmation of these observations. Hassler¹⁰has postulated that paralysis