NREM sleep spindles and slow wave sleep in younger and elderly women: an investigation of their influence on declarative memory consolidation

Previous research shows that slow wave sleep (SWS) and sleep spindles play an essential role in declarative memory consolidation. However, this role is not well understood in the ageing women. With advancing age, SWS and sleep spindles undergo significant decreases in duration and density, while there is a simultaneous decline in declarative memory. The primary aim of this research was to investigate the relationship between sleep architecture, sleep spindle activity, and declarative memory retention in two groups of women: 14 younger (M = 20.5±1.28 years) and 14 older females (M = 63.14±2.03 years). Participants underwent polysomnography on a baseline and experimental night and encoded a list of word-pairs of graded difficulty on the experimental night. Word-pair type included integrative, concrete and low concrete measures. Memory retention was then assessed pre- and post-sleep. Our results confirm the characteristic age-related decrease in SWS and sleep spindle activity in older adults. In the older group, SWS positively correlated with concrete word-pair retention, while spindle density and the number of spindles positively correlated with overall retention. In addition, the percentage change in spindle density, slow and fast density, and fast intensity from baseline to experimental night positively correlated with low concrete word-pairs. Finally, in the younger group, the number of spindles positively correlated with low concrete word-pairs and the percentage change in fast and slow spindle intensity correlated with concrete word-pair retention. Although younger women recalled more word-pairs than older women in both conditions, memory retention was largely preserved in both groups after sleep