Sleep alterations are related to cognitive symptoms in Parkinson's disease

Sleep disorders are frequent and early non-motor symptoms of Parkinson's disease (PD). As a consequence of histopathological changes, the regulation of rapid eye movement (REM) sleep is affected in PD causing REM sleep behaviour disorder in about half of the patients. Considering the well-known role of sleep in memory formation processes, our aim was to investigate the relationship between sleep alterations and cognitive performance to elucidate the possible association between sleep, and especially REM sleep changes and cognitive dysfunction in PD.We investigated 25 PD patients and 20 healthy controls. All participants underwent a 24-hour-long 19-channel polygraphic EEG recording, neurological, neuroimaging and neuropsychological examination. The visually analysed sleep-EEG and neuropsychological data were statistically evaluated.We found significant negative correlation between verbal fluency and REM sleep ratio as well as average REM sleep period duration in the whole sample. The intergroup analysis showed significant decrease of REM and N3, but increase of N2 sleep ratio, and significantly lower scores in the verbal fluency in PD compared to healthy controls. In the PD group we found significant reduction of N3 sleep ratio in patients with REM sleep behaviour disease compared to patients without it.The negative correlation between verbal fluency performance and REM sleep duration suggests the role of decreased REM sleep in cognitive dysfunction in PD. The early involvement of REM sleep regulation with parallel executive dysfunction in PD emphasise the important role of REM sleep deterioration in the neurodegenerative process of PD.