Memory reactivation in slow wave sleep enhances relational learning

Sleep has been shown to boost the integration of memories, and thus to facilitate relational learning. This benefit is thought to rely upon memory reactivation during non-REM sleep. We set out to test this possibility by explicitly cueing such reactivation using a technique called targeted memory reactivation (TMR), in which sounds are paired with learned material in wake and then softly played back to the participant in sleep, triggering reactivation of the associated memories. Specifically, we tested whether TMR during slow wave sleep leads to enhancements in inferential thinking in a transitive inference task. Because the Up-phase of the slow oscillation is more responsive to external cues than the Down-phase, we also asked whether stimulation at this specific phase is more beneficial for such integration. Our data show that Up-phase TMR boosts the ability to make inferences, but only for the most distant inferential leaps. Such stimulation was also associated with detectable memory reinstatement, whereas Down-phase stimulation produced no such trace and led to below-chance performance. These findings demonstrate that cueing memory reactivation at the right time points in sleep can provide a direct benefit to difficult relational learning problems. Significance StatementMemory reactivation in sleep is thought to be important for integrative thinking. We examined this by explicitly cueing reactivation of a transitive inference task during slow wave sleep using Targeted Memory Reactivation (TMR). Because TMR at different phases of the slow oscillation has different impacts, we cued different hierarchies at Up and Down phases. Up-phase TMR enhanced inferential performance and was associated with classifiable memory reactivation. Conversely, Down-phase TMR lead to a short-term impairment in inferential thinking and no detectable reactivation. These findings provide the first evidence that TMR can boost transitive inference and is thus important for integration and reasoning.