Sleep-like slow waves during wakefulness are associated with hallucinations and poorer cognition in Parkinson’s disease

Slow waves during sleep are fundamental for neural homeostasis, metabolic regulation, and waste clearance and are known to be altered in neurodegenerative diseases. Sleep-like slow waves (SLSWs) have been observed in awake, healthy individuals, where they are linked to fluctuations in vigilance and mind-wandering. Whether SLSWs are altered in Parkinson’s disease (PD), and whether such alterations contribute to psychiatric or cognitive complications, remains unknown. In a cohort of 84 nondemented patients with PD and 30 healthy older adults, we found that SLSWs occurred more frequently in patients with PD. Hallucinatory traits in patients with PD were associated with higher SLSW amplitude, especially over frontocentral regions. Moreover, more prominent SLSWs were associated with poorer cognitive functions. We conclude that, whereas slow waves during sleep have positive physiological functions, exacerbated diurnal SLSWs may reflect responses related to PD neuropathology, at the cost of hallucinations and reduced cognitive function.