Date of Award

Summer 8-15-2016

Author's School

Graduate School of Arts and Sciences

Author's Department

Movement Science

Degree Name

Doctor of Philosophy (PhD)

Degree Type



Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by cell death in the substantia nigra pars compacta, resulting in motor symptoms of tremor, rigidity, bradykinesia and gait impairment. Freezing of gait (FOG) is one serious gait disturbance, characterized by a transient inability produce effective stepping during walking and turning, and affects roughly half of people with PD at some point during their disease. Despite the ongoing research on the behavioral, neurological, and cognitive characteristics of people with FOG (PD+FOG), the mechanisms underlying freezing are still poorly understood. The overall aim of this work was to further investigate motor behavior in PD+FOG to provide insight into its potential mechanisms. The first experiment investigated possible cerebellar dysfunction in PD+FOG by examining visuomotor adaptation, a well-known cerebellar-dependent process. We found that there were no differences in reaching or walking adaptation between freezers and non-freezers, however non-freezers exhibited smaller after-effects compared to freezers and healthy older adults. Furthermore, adults with PD, as well as older and younger adults adapt walking patterns slower than reaching patterns, indicating walking is a more complex task requiring greater sensorimotor processing to modify. Overall, this study showed that cerebellar function, in terms of its role in sensorimotor adaptation, is relatively preserved in PD and FOG.

In the second experiment, we examined motor automaticity of saccadic eye movements and reaching. Reduced automaticity is a likely motor-cognitive mechanism that contributes to freezing behavior, however automaticity in other motor systems has yet to fully described. Using an anti-saccade task, we found that PD+FOG participants were slower to respond to both automatic and non-automatic eye movements, and had increased saccade velocity variability compared to PD-FOG and controls. These changes were not related to disease severity or general cognition. In contrast, both PD groups were slower to execute (greater latency) reaching movements during both pro- and anti-reaching, but no freezer non-freezer differences were noted. PD+FOG reached with lower peak velocity compared to older adults but were similar to PD-FOG during both automatic and non-automatic conditions. These data show that changes in automaticity and control exist outside locomotor centers, indicating freezing may be a global motor disturbance. Altogether, the work in this dissertation furthers our knowledge on motor control in PD+FOG and provides additional evidence that freezing affects non-gait motor function.


English (en)

Chair and Committee

Gammon M. Earhart

Committee Members

Tamar Hershey, Catherine E. Lang, Michael J. Mueller, Joel Perlmutter


Permanent URL: https://doi.org/doi:10.7936/K79Z938X