Targeted memory reactivation of a serial reaction time task in SWS, but not REM, preferentially benefits the non-dominant hand

Targeted memory reactivation (TMR) is a technique by which sounds paired with learned information can be used to cue neural reactivation of that information during sleep. While TMR in slow-wave sleep (SWS) has been shown to strengthen procedural memories, it is unclear whether TMR in rapid eye movement (REM) sleep, a state strongly associated with motor consolidation, provides equivalent benefit. Furthermore, it is unclear whether this technique influences dominant and non-dominant hands equally. We applied TMR of a two-handed serial reaction time task (SRTT) during either SWS or REM in thirty-two human right handed adults (sixteen female) to examine the impact of stimulation in each sleep stage on right (dominant) and left hands. While TMR in SWS led to strong benefits in reaction times and sequence-specific skill, equivalent cueing in REM led to no benefit at all, suggesting that reactivation in this sleep stage is not important for the SRTT. Event-related potentials elicited by TMR cues for left and right hand movements differed significantly in REM, but not SWS, showing that these cues are at least processed in REM. Interestingly, TMR benefits were apparent only in the non-dominant hand, potentially due to the weaker performance measured in this hand at the outset. Overall, these findings suggest that memory replay in SWS, but not REM, is important for consolidation of the SRTT, and TMR-cued consolidation is stronger in the non-dominant hand. Significance statement Targeted memory reactivation (TMR) in sleep leads to memory consolidation, but many aspects of this process remain to be understood. We used TMR of a bimanual serial reaction time task to show that behavioural benefit is only observed after stimulation in SWS, even though electrophysiology shows that the TMR cues are processed in REM. Importantly, TMR selectively benefitted the non-dominant hand. These findings suggest that TMR in REM does not benefit this serial reaction time task, and that TMR in SWS preferentially consolidates weaker memory traces relating to the non-dominant hand.