Investigating the effect of task engagement during intertrial rest periods on micro offline gains

Explicit motor sequence learning (ESL) consolidation manifests as skill improvements during rest periods that last minutes or longer. However, recent evidence suggests that ESL improvements also occur during inter-trial rest periods that last seconds (micro offline gains; MOGS). While indirect evidence supports that MOGS is a phenomenon tied to brief periods of wakeful rest, this hypothesis has never been directly tested. Prior studies suggest that MOGS and sequence learning in general rely on associative memory processes that link sequence elements across time and space. However, evidence supporting this hypothesis in healthy humans is lacking. We reasoned that if wakeful rest during inter-trial ESL periods is necessary for MOGS, replacing these periods with an engaging task should degrade MOGS. Additionally, we explored whether associative processes support MOGS, predicting that associative memory encoding during inter-trial periods would further degrade MOGS. To this end, we compared the performance of three groups that differed only in whether inter-trial periods included no task (REST), an associative encoding task (ENC), or a semantic judgment task (SEM). We identified no significant group differences in ESL or MOGS, which were confirmed by Bayesian analyses. These results are consistent with the notion that MOGS capture inter-trial performance changes rather than a rapid form of consolidation that requires rest or depends on associative memory processes.