Pallidum and Muscle Tone

Abstract

In contrast to the rigor induced by diffuse diseases of the pallidum, circumscribed lesions of the ansa lentiformis and of the adjoining part of the pallidum are not followed by increase of muscle tone; in some instances even a reduction of the rigor can be observed in patients suffering from paralysis agitans or postencephalitic parkinson-ism. These observations are substantiated by recordings of the resistance to passive movements by means of a specially devised myotonograph. The diminution of the bradykinesis following ansotomy in patients suffering from postencephalitic parkinsonism or paralysis agitans is in agreement with these findings; however, bradykinesis may also be favorably influenced in the absence of rigor. A working hypothesis is offered suggesting that the various efferent fibers of the pallidum are functionally not equivalent; besides tonus inhibiting fibers, there seem to exist, particularly in the ansa lentiformis, pallidofugal fibers that conduct facilitating impulses to lower tonus maintaining reflex arcs.