It has been proposed that recently acquired memories would be reinstated during a spindle oscillation and subsequently reprocessed during the following refractory period, thereby protecting memory reinstatement from potential interference ( Antony et al., 2018, 2019). This ISI is believed to reflect a refractory period. Specifically, during NREM sleep spindles tend to cluster into trains of two or more, separated by inter-spindle intervals (ISI) of 3 to 6 s ( Evans and Richardson, 1995 Achermann and Borbély, 1997 Antony et al., 2018). In the last few years, it has been argued that the rhythmicity in their occurrence may also be a relevant parameter influencing memory stabilization ( Lecci et al., 2017 Antony et al., 2018 Boutin and Doyon, 2020). Individual spindles may promote memory consolidation through the modulation of intrinsic features such as their amplitude ( Barakat et al., 2012 Bergmann et al., 2012 Boutin et al., 2018b), duration ( Morin et al., 2008 Laventure et al., 2016), power ( Ngo et al., 2020) and density ( Nishida and Walker, 2007 Barakat et al., 2011 Albouy et al., 2013 Solano et al., 2021). Sleep spindles are bursts of oscillatory thalamocortical activity thought to support the reactivation of newly formed memories ( Rasch and Born, 2013 Staresina et al., 2015 Schönauer, 2018).
The fact that the level of spindle-SO synchrony predicts overnight memory retention opens the possibility that common mechanisms operate in the stabilization of declarative and motor memories.
Recently, we have shown that motor learning, specifically visuomotor adaptation (VMA), also promotes the coupling between spindles and SOs ( Solano et al., 2021).
Overnight reactivation of hippocampal memories appears to depend on sleep spindles, slow oscillations (SO) and their precise synchrony ( Maingret et al., 2016 Ladenbauer et al., 2017 Helfrich et al., 2018 Muehlroth et al., 2019 Navarro-Lobato and Genzel, 2019). The last decade has seen remarkable progress in the identification of the neural signatures of sleep-dependent consolidation. Our work opens the possibility that the periodicity of NREM oscillations may be relevant in the stabilization of procedural memories. The fact that these features increased as a function of train length, provides evidence supporting a biological advantage of this temporal arrangement. Interestingly, spindles grouped in a cluster showed greater amplitude and duration than isolated spindles. In agreement with our previous work, this modulation was observed over the contralateral hemisphere to the trained hand, and predicted overnight memory retention. We found that VMA increased the proportion of spindles and spindle-SO couplings in trains. Here, we examined if VMA learning promotes the temporal organization of sleep spindles into trains. Yet, growing evidence suggests that the rhythmicity in spindle occurrence may also influence the stabilization of declarative and procedural memories. Recently, we have shown that visuomotor adaptation (VMA) learning increases the density of spindles and promotes the coupling between spindles and slow oscillations, locally, with the level of spindle-SO synchrony predicting overnight memory retention.
Sleep spindles are thought to promote memory consolidation.
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