Two behavioral phenomena characterize human motor memory consolidation: diminishing susceptibility to interference by a subsequent experience and the emergence of delayed, offline gains in performance. A recent model proposes that the sleep-independent reduction in interference is followed by the sleep-dependent expression of offline gains. Here, using the finger-opposition sequence–learning task, we show that an interference experienced at 2 h, but not 8 h, following the initial training prevented the expression of delayed gains at 24 h post-training. However, a 90-min nap, immediately post-training, markedly reduced the susceptibility to interference, with robust delayed gains expressed overnight, despite interference at 2 h post-training. With no interference, a nap resulted in much earlier expression of delayed gains, within 8 h post-training. These results suggest that the evolution of robustness to interference and the evolution of delayed gains can coincide immediately post-training and that both effects reflect sleep-sensitive processes.And here is a graphic summarizing the results from the review by Diekelmann and Born:
Two ways of consolidating memory of finger tapping skill.
(a) Evolution of finger-to-thumb tapping skill under three experimental key conditions. From top to bottom: after training a specific sequence (Sequence A) in the morning and a first retest 8 h later, a distinct gain in performance developed at the second retest following overnight sleep (purple). Interference by training on a different sequence (Sequence B) 2 h after training of Sequence A completely abolished any sleep-dependent overnight gain developing between the first and second retest (blue). This overnight gain was restored when subjects napped for 90 min between training of Sequence A and interference training on Sequence B (green). (b) Model of skill memory consolidation. Representations of finger tapping skill are encoded in a temporary store. Stabilization (resistance to interference) of the representation can be achieved either through time-dependent synaptic consolidation (dark green) in the temporary buffer or through sleep-dependent system consolidation (red) that leads to a redistribution of the representation to different neuronal networks for long-term storage. Memory enhancement (delayed gains in performance) requires sleep-dependent system consolidation.