REM density in Parkinson's disease: association with motor, cognitive, autonomic function, and dopaminergic medication.

Recent work has shown that REM density, defined as the number of rapid eye movements per REM sleep minute, is decreased in people with Parkinson's disease (PD) and is associated with greater bradykinesia, suggesting a motor component. This study explored the association of REM density with gait, cognitive function, and heart rate variability (HRV). Seventy-seven PD patients underwent overnight polysomnography. Gait was evaluated using wearable technology during preferred-speed walking and while walking with a cognitive task (dual tasking). Lower REM density was associated with poorer gait and mobility, particularly during dual-tasking and turning, but not with HRV. Patients taking evening slow-release dopaminergic medication showed higher REM density compared to drug-naïve patients or those on daytime medication. These findings highlight the role of motor and cognitive functions in the generation of rapid eye movements in PD. Administration of evening medications appears to improve REM density, likely by alleviating motor control deficits.