Memory performance in sleep-impaired patients with Parkinson's disease and the influence of depression

Neuropsychological investigations revealed deficits of memory-, visuospatial- and frontal lobe functions already in earlier stages of Parkinson's disease. Sleep disturbances were found in 67% to 98% of this group of patients. A tendency towards depressive mood seems to play an important role in this context. To explore the relation between sleep disturbance, depression and cognitive impairment we examined 20 patients with Parkinson's disease and 10 control subjects. Both groups were instructed to rate their subjective sleep quality on a scale. They had to answer to Beck's Depression Inventory and were subject to a standardised multiple word knowledge test (MWT-B) for estimating the level of intelligence. In addition, verbal and visual short- and long-term memory was examined with the Rey Auditory Verbal Learning Test (RAVLT) and the Rey Visual Design Learning Test (RVDLT) respectively. Implicit memory performance was tested with the Gollin figures. Sleep quality in Parkinson patients was significantly worse than in healthy controls. Moreover, within the Parkinson group, verbal proactive interference significantly correlated with increasing depression values. Visual short-term memory as well as visual long-term memory performance deteriorated with increasing depression. Furthermore, patients with reduced sleep quality showed poorer implicit memory performance.