Sleep and cognition in older adults: Does depression matter? An actigraphy and polysomnography study

The impact of sleep on cognition is well recognised, although research in older adults is lacking, as are investigations into how depression might impact on this relationship. This study assessed the relationship between sleep (assessed with actigraphy and polysomnography) and cognitive performance in older adults (50–78 years) with (n = 10) and without (n = 33) a current diagnosis of Major Depressive Disorder (MDD). There were associations between sleep-wake patterns and cognition across the whole sample: time spent awake after sleep onset (WASO) was associated with speed of responding on vigilance tasks and accuracy on delayed recall tasks; sleep efficiency and total sleep time (at trend-level) were linked to working memory accuracy. Examination of the impact of depression on the relationship between sleep and cognition was explored using moderation analysis. Current depression was a significant moderator of the relationship between sleep-wake patterns (assessed with actigraphy), but not sleep architecture (assessed with PSG), and cognition. That is, there was a different pattern of association of sleep-wake patterns and cognitive performance depending on depression status. Specifically, in the MDD group, sleep-wake patterns were linked to speed of processing on cognitive tasks, whereas in the not currently depressed group, sleep-wake patterns were linked to performance accuracy. In conclusion, it was found that depression impacted on the relationship between sleep and cognition but questions remain regarding the nature of the relationship between sleep and cognition in older adults. Given that sleep problems are potentially modifiable risk factors for cognitive impairment, these findings point to the importance of assessing sleep in both depressed and healthy older adults.