ADAPTIVE-CHANGES IN RESPONSES TO REPEATED LOCOMOTOR PERTURBATIONS IN CEREBELLAR PATIENTS

This study examined the responses of cerebellar patients and a group o f age- and sex-matched control subjects to repeated changes in treadmi ll speed in order to test whether cerebellar patients can adapt their gait to this type of perturbation and, if so, whether their responses are comparable to those of controls. While the subject walked on the t readmill, a perturbation consisting of a sudden slowing of the treadmi ll followed by a sudden increase back to the original speed was applie d repeatedly at a specific time during the step cycle. Both the contro l subjects and cerebellar patients were able to compensate for the per turbations by minimizing their postural sway and changing step length. However, the nature of the compensatory changes in step length differ ed between these subject groups. Control subjects compensated for the perturbation by consistently using the same leg to initiate the respon se to the perturbation and by adapting a pattern of stepping such that the EMG characterizing the response occurred in a manner that was ent rained to the timing of the normal locomotor cycle. In contrast, the p atients, although undergoing modifications in step length, employed a much less consistent motor pattern from trial to trial than that of th e normal subjects. An inconsistent pattern among their responses was a pparent in both the analysis of stepping and in the EMG activity of th e gastrocnemius and anterior tibial muscles. These results suggest tha t, although the cerebellar patients can adapt their behavior in respon se to locomotor perturbations, they do not establish a motor pattern c omparable to that employed by normal subjects.