Cued memory reactivation during motor imagery practice influences early improvement of procedural skill learning

Reactivation processes are fundamental for procedural memory improvement. Targeted memory reactivation (TMR) influences memory consolidation through the re-exposure to certain perceptual components present in a previous phase of associative learning. On the other hand, motor imagery (MI) affects procedural skills through a repeated mental simulation of a pre-learned movement without physically moving. Both for TMR and MI, performance improvement has proven to be associated with an induction of reactivation processes. The positive effect of TMR is widely acknowledged in sleep. Here, we measured its impact on procedural learning during waking, in particular during MI practice, in line with the hypothesis that the exogenously induced involuntary reactivations through TMR could add up to the endogenous and voluntary reactivations induced by MI. Therefore, we assessed the influence on performance on a sequential finger tapping task of an auditory TMR during MI practice. It was compared to four conditions: (i) MI alone, (ii) MI during an incompatible sound stimulation, (iii) a mere video viewing and (iv) an auditory TMR during a video viewing. Results showed that the TMR + MI condition determined the largest early performance improvement as indexed by the combined measure of speed and accuracy (number of correct sequences typed in the task). We propose that TMR may enhance the effectiveness of MI protocols, and that MI could represent an optimal time window during wakefulness to take advantage of the effects of TMR.