Excessive daytime sleepiness in parkinsonism is associated with cortical and basal ganglia beta oscillatory activity

Excessive daytime sleepiness, i.e., the inability to sustain wakefulness during the day, is a common Parkinson's disease (PD) non-motor symptom. Elevated cortico-basal ganglia beta oscillatory power (8-35 Hz) is a pathophysiological signature of PD motor signs. The relationship between beta oscillatory power and daytime sleepiness, however, remains unclear. Here, we examined the relationship between beta power and daytime vigilance in parkinsonian nonhuman primates. We administered dopaminergic medication to alter cortico-basal ganglia beta power and measured its effect on daytime vigilance. The beta power from motor cortex (MC) and subthalamic nucleus (STN), and wake quantity were derived in the following conditions: OFF-medication, ON-medication, and decay of medication effect. STN low-beta (8-20 Hz) power negatively correlated with wake quantity, suggesting that elevated STN low-beta power could disrupt sustenance of wakefulness. The cortical low-beta power did not correlate with wakefulness. Interestingly, STN and MC high-beta (21-35 Hz) power positively correlated with wake quantity. Our data provide evidence for an association between beta power and daytime vigilance in parkinsonism in addition to its known relationship with PD motor signs. These findings could inform targeted treatments to promote wakefulness in PD by selectively suppressing (e.g., low-beta) and/or amplifying (e.g., high-beta) cortico-basal ganglia beta oscillatory power.