The College of Education announces the final Dissertation of

Benjamin Brett

for the degree of Doctor of Philosophy

November 17, 2017 at 1:00 pm in Ball Hall 103

Major Advisor: Suzanne Lease, PhD

Neurocognitive Impairment in Parkinson’s Disease Patients: Assessing the Unique Contributions of Depression and Fatigue While Controlling for Disease Severity

ABSTRACT: Background: While individuals diagnosed with Parkinson’s disease (PD) often experience cognitive deficits, depression, and fatigue, the relationships among these nonmotor sequelae throughout the progression of the disease are unclear. Objective: To examine the relationships among disease severity, depression, and fatigue and investigate the independent contributions of depression and fatigue to a composite measure of cognitive impairment, when controlling for disease severity in PD patients. Methods: A mixed retrospective and prospective sample of PD patients completed a comprehensive neuropsychological battery, as well as self-report measures of depression and fatigue. Cognitive impairment was represented by a summary statistic, or cognitive impairment index (CII). A hierarchal linear regression model, controlling for disease severity, examined the unique contributions of depression and fatigue on cognitive impairment. A Pearson correlation examined the relationship between depression and fatigue. Results: At step one, disease severity significantly contributed to the model, F(1, 41) = 48.06, p < .001, accounting for 52.8% of the variance in cognitive impairment. Introduction of depression and fatigue explained an additional 7.2% of the variance and this change in R2 was significant F(2,39) = 4.68, p < 0.05. Both depression, t = 2.751, B = 0.30, p < 0.01, and fatigue, t = -2.03, B = -0.21, p = 0.049 significantly contributed to the model in addition to variance accounted for by disease severity. Conclusions: Findings suggest that depression is uniquely associated with cognitive impairment observed in PD patients independent of disease severity or level of fatigue. Interventions targeted towards depression may improve cognitive functioning.