The Relationship between Circadian Dysfunction and Cognitive Impairment in Individuals with Parkinson’s Disease

Parkinson’s Disease (PD) is a brain disorder associated with a variety of motor (e.g., rigidity, tremor) and nonmotor (e.g., cognitive impairment, sleep dysfunction) symptoms. Recent evidence suggests that PD patients may also have dysfunctional circadian rhythms: oscillators responsible for many behavioral and physiological functions (e.g., sleep-wake cycle, cognitive performance). No study to date has measured both circadian rhythms and cognitive functioning in the same group of PD patients. This was the aim of the current project. The archival data set included 34 PD patients and 12 normal control participants (NC) matched by age and education. Cognition was measured through a series of neuropsychological tests measuring memory and executive functioning. Archival circadian rhythm data, collected through watch actigraphy, was analyzed using three nonparametric variables: relative amplitude (RA), interdaily stability (IS), and intradaily variability (IV). Higher RA and IS values indicate a more stable rhythm, while higher IV values indicate a less stable rhythm. Patients with PD had significantly higher RA values than NCs; however, there was no significant difference between PDs and NCs in IS or IV values. There was a significant positive correlation between executive functioning and RA and IS values in PDs. No significant correlations were found between executive functioning and IV values or between working memory and RA, IS, or IV values among PDs. This preliminary evidence suggests that disrupted circadian rhythm in PD patients may be related to cognitive impairment. Future research should investigate this potential link by using additional and more sophisticated circadian rhythm measures. This, in turn, could shed more light on the role circadian rhythm dysfunction plays in the cognitive impairment of PD patients and thus, highlight the potential need for new treatment and intervention strategies aimed at improving the quality of life of these individuals.