Delayed Feedback as a Possible Mechanism in Parkinsonism

Many aspects of human behavior may be viewed as the functioning of feedback concrol systems (Powers, Clark, & McFarland, 1960). This paper is concerned with some temporal aspects of feedback factors, which might explain parkinsonian disability. Parkinsonism is a disorder involving a loss of normal synchrony beween agonist and antagonisc musculature and is characterized by motor signs such as muscle rigidity, tremor, and slowness of movement. In advanced stages the patient can neicher walk nor perform coordinaced hand and arm lnovemencs for such activicies as feeding or dressing himself. The disease is considered to be the result of malfunction of the extrapyramidal syscem but there is no complete neurophysiological explanation of the mechanism by which this malfunction produces the symptoms. It has been argued chat che motor symptoms result from a loss of normal inhibicion of antagonistic reflexive movement (Denny-Brown, 1950). The nature of che inhibirion and disinhibicion has noc been elaborated, however. The present auchors believe thac che loss of at least some of the normal patterns of control might be explained by the hypothesis of a simple perceptual malfunction, an abnormal delay in proprioception. The theory which follows draw heavily on che analogies of experimentally induced disabilities and on evidence concerning normal perceptual delay. While possible neurophysiological mechanisms are described, the theory is justified on the grounds of parsimony and on successful experimental tests rather than on the grounds of excluding alternative hypotheses.