Variable training but not sleep improves consolidation of motor adaptation

How motor memory consolidates still remains elusive. Consolidation of motor skills has been shown
to depend on periods of sleep. Conversely, motor adaptation during tasks not dependent on the
hippocampus may not depend on sleep. Some research suggests that the training schedule affects the
sleep dependency of motor adaptation tasks. Here, we investigated whether sleep differentially affects
memory consolidation that depends on the training schedule. Healthy men were trained with their
dominant, right hand on a force-field adaptation task and re-tested after an 11-h consolidation period
involving overnight sleep (Sleep) or daytime wakefulness (Wake). Retesting included a transfer test of
the non-dominant hand. Half of the subjects in each group adapted to different force-field magnitudes
during training with low inter-trial force variability (Sleep-Blocked; Wake-Blocked), and the other half
were trained with a high-variability schedule (Sleep-Random; Wake-Random). EEG was recorded during
task execution and overnight polysomnography. Consolidation was comparable between Wake and
Sleep groups, although performance changes over sleep correlated with sleep spindles nesting in slowwave
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upstates. Higher training variability improved retest performance, including transfer learning, and
these improvements correlated with higher alpha power in contralateral parietal areas. These enhanced
consolidation effects might be fostered by feedback rather than feedforward mechanisms.