Abstract
Sleep has been shown to stabilize memory traces and to protect against competing interference in both the procedural and declarative memory domain. Here, we focused on an interference learning paradigm by testing patients with primary insomnia (N = 27) and healthy control subjects (N = 21). In two separate experimental nights with full polysomnography it was revealed that after morning interference procedural memory performance (using a finger tapping task) was not impaired in insomnia patients while declarative memory (word pair association) was decreased following interference. More specifically, we demonstrate robust associations of central sleep spindles (in N3) with motor memory susceptibility to interference as well as (cortically more widespread) fast spindle associations with declarative memory susceptibility. In general the results suggest that insufficient sleep quality does not necessarily show up in worse overnight consolidation in insomnia but may only become evident (in the declarative memory domain) when interference is imposed.
Highlights
Positive effects of sleep on memory consolidation are compellingly demonstrated in a number of studies
Regarding the experimental night following declarative word-pair learning differences in sleep parameters between healthy controls and insomnia patients were found for sleep efficiency (t43 = 2.818, p = 0.008) and wake after sleep onset (WASO) (t43 = 23.259, p = 0.003) again indicating better sleep quality for healthy sleepers
Finger Tapping Task (FTT) Overall, behavioral effects revealed a main effect for overnight performance change (TIME 1) (F(1,46) = 15.198, p,0.001) indicating an increase in performance in healthy controls (t20 = 23.86, p = 0.001; mean evening = 94.08627.26, mean morning = 103.27631.63) and a trend toward an increase in insomnia patients
Summary
Positive effects of sleep on memory consolidation are compellingly demonstrated in a number of studies (for review see [1]). It has been shown that memory performance is enhanced after periods of sleep relative to equal amounts of wakefulness. This evidence has been found for different kinds of memory contents. At least for declarative contents it has been shown that reactivations (especially in hippocampal regions) are temporally linked to thalamo-cortically generated sleep spindles [14,15,16,17]. [18]) and may serve as a marker for successful memory consolidation during sleep This involves the redistribution of new and fragile memory traces into stable cortical memory systems which lead to facilitated long term accessibility and reduced susceptibility to interference. For the declarative memory domain, and in accordance with known functional specializations, Clemens et al [20] for example reported spindle foci over left frontocentral areas for verbal declarative material
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