Sleep Spindle Density and Temporal Clustering Are Associated with Sleep-Dependent Memory Consolidation in Parkinson’s Disease

Study Objectives: Sleep is required for successful memory consolidation. Sleep spindles, bursts of oscillatory activity occurring during non-rapid eye movement sleep, are known to be crucial for this process and, recently, it has been proposed that the temporal organization of spindles into clusters might additionally play a role in memory consolidation. In Parkinson 's disease, spindle activity is reduced, and this reduction has been found to be predictive of cognitive decline. However, it remains unknown whether alterations in sleep spindles in Parkinson 's disease are predictive of sleep-dependent cognitive processes such as memory consolidation, leaving open questions about the possible mechanisms linking sleep and a more general cognitive state in Parkinson 's patients. Methods: The current study sought to fill this gap by recording overnight polysomnography and measuring overnight declarative memory consolidation in a sample of 35 patients with Parkinson 's. Memory consolidation was measured using a verbal paired-associates task administered before and after the night of recorded sleep. Results: We found that lower sleep spindle density at frontal leads during non-rapid eye movement stage 3 was associated with worse overnight declarative memory consolidation. We also found that patients who showed less temporal clustering of spindles exhibited worse declarative memory consolidation. Conclusions: These results suggest alterations to sleep spindles, which are known to be a consequence of Parkinson 's disease, might represent a mechanism by which poor sleep leads to worse cognitive function in Parkinson 's patients.