Abstract
There is growing evidence of the active involvement of sleep in memory consolidation. Besides hippocampal sharp wave-ripple complexes and sleep spindles, slow oscillations appear to play a key role in the process of sleep-associated memory consolidation. Furthermore, slow oscillation amplitude and spectral power increase during the night after learning declarative and procedural memory tasks. However, it is unresolved whether learning-induced changes specifically alter characteristics of individual slow oscillations, such as the slow oscillation up-state length and amplitude, which are believed to be important for neuronal replay. 24 subjects (12 men) aged between 20 and 30 years participated in a randomized, within-subject, multicenter study. Subjects slept on three occasions for a whole night in the sleep laboratory with full polysomnography. Whereas the first night only served for adaptation purposes, the two remaining nights were preceded by a declarative word-pair task or by a non-learning control task. Slow oscillations were detected in non-rapid eye movement sleep over electrode Fz. Results indicate positive correlations between the length of the up-state as well as the amplitude of both slow oscillation phases and changes in memory performance from pre to post sleep. We speculate that the prolonged slow oscillation up-state length might extend the timeframe for the transfer of initial hippocampal to long-term cortical memory representations, whereas the increase in slow oscillation amplitudes possibly reflects changes in the net synaptic strength of cortical networks.
Highlights
For a long time, sleep has been seen as a mere state of passiveness, which only serves resting and recovery purposes
Studies using single-unit recordings in rodents have shown that after encoding, during quiet wakefulness or subsequent sleep, newly acquired memory traces become spontaneously and repeatedly reactivated. These reactivations are most prominent within the fast-learning hippocampus and are strongest during the occurrence of hippocampal sharp wave-ripple complexes [3,4,5]
During slow-wave sleep (SWS), hippocampal ripples - recorded in rats and humans were found to be temporally linked to thalamo-cortically generated sleep spindles [6,7], which are proposed to support synaptic plasticity at the neocortical level [8]
Summary
Sleep has been seen as a mere state of passiveness, which only serves resting and recovery purposes. According to the “active system consolidation” hypothesis, sleep actively strengthens and restructures memories and thereby promotes the consolidation of newly acquired memory traces [1]. It is believed that new, declarative knowledge is initially encoded in a fast-learning temporary memory storage as well as in a parallel slow-learning long-term memory storage, namely the hippocampus and the neocortex, respectively [2]. Studies using single-unit recordings in rodents have shown that after encoding, during quiet wakefulness or subsequent sleep, newly acquired memory traces become spontaneously and repeatedly reactivated. These reactivations are most prominent within the fast-learning hippocampus and are strongest during the occurrence of hippocampal sharp wave-ripple complexes [3,4,5]. During slow-wave sleep (SWS), hippocampal ripples - recorded in rats and humans were found to be temporally linked to thalamo-cortically generated sleep spindles [6,7], which are proposed to support synaptic plasticity at the neocortical level [8]
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