| A primary consequence of cerebellar damage in humans is gait ataxia, characterized by a veering, stumbling path, widened base of support, irregular foot placement, and abnormal coordination across multiple joints of the leg. The purpose of this dissertation was to examine the role of the cerebellum in controlling human walking and to determine possible neural mechanisms of cerebellar gait ataxia. Specifically, this dissertation was undertaken to determine the extent to which cerebellar gait ataxia is related to deficits of balance versus leg coordination, whether ataxia during obstacle avoidance is associated with impaired leg dynamics, and whether cerebellar damage impairs locomotor adaptation to novel conditions. Three studies were undertaken to address these issues. The first study (Chapter 2) examined contributions of balance and voluntary leg control deficits to human cerebellar gait ataxia. Results demonstrated that gait ataxia was strongly related to impairments of balance but not to impairments of voluntary leg control, highlighting the relative importance of more medial cerebellar regions during unperturbed locomotion. The second study (Chapter 3) tested the role of the cerebellum in controlling multijoint leg dynamics during obstacle avoidance in the context of locomotor versus isolated stepping movements. Findings indicated that control of intersegmental dynamics may be context-specific, with the cerebellum playing a critical role controlling multijoint dynamics during voluntary, isolated leg movements, but less so when the movements occur within the locomotor pattern. The third study (Chapter 4) examined the role of the cerebellum during adaptation to a prism-induced visual shift in walking direction. Results showed that cerebellar damage impaired the extent, rate, and storage of the adaptation, as well as the generalization to unexposed arm movements. Taken together, these studies provide novel and valuable insights into the poorly understood topic of cerebellar control of human locomotion. Findings support a hypothesis that the cerebellum helps maintain appropriate postural control during locomotion, generate accurate multijoint dynamics during adjustments to voluntary leg movements, and adapt locomotor patterns to novel visual conditions. This dissertation was supported in part by NIH grants T32HD007434, K01HD001199, and R0IHD040289, and by PODS-I and PODS-II scholarships awarded from the APTA. |
