Offline rTMS of the primary and premotor cortices does not impact motor sequence memory consolidation despite modulation of corticospinal excitability

Motor skills are acquired and refined across alternating phases of practice (online) and subsequent consolidation in the absence of further skill execution (offline). Both stages of learning are sustained by dynamic interactions within a widespread motor learning network including the premotor and primary motor cortices. Here, we aimed to investigate the role of the dorsal premotor cortex (dPMC) and its interaction with the primary motor cortex (M1) during motor memory consolidation. Forty-eight healthy human participants (age 22.1 ± 3.1 years) were assigned to three different groups corresponding to different offline repetitive transcranial magnetic stimulation (rTMS) interventions. 1Hz rTMS of either left dPMC, left M1, or sham rTMS was applied immediately after explicit motor sequence training with the right hand. Motor evoked potentials were recorded before training and after rTMS to assess changes of corticospinal excitability (CSE). Participants were retested on the motor sequence after eight hours to assess consolidation. While CSE was not modulated in the sham rTMS group, post-training rTMS increased and decreased CSE when targeting dPMC and M1, respectively. However, all groups demonstrated similar significant offline learning over the day indicating that offline consolidation was not modulated by the post-training rTMS interventions despite evidence of an interaction of dPMC and M1 at the level of CSE. Motor memory consolidation ensuing explicit motor sequence training seems to be a rather robust process that is not affected by rTMS-induced perturbations of dPMC or M1. Findings further indicate that consolidation of explicitly acquired motor skills is neither mediated nor reflected by post-training CSE.