Role of trained primary motor cortex in intermanual transfer of a newly learned motor skill

Details

Supervisors

Duque Julie

Faculty

Faculté de pharmacie et des sciences biomédicales

Degree label

Master [120] en sciences biomédicales, à finalité approfondie

Abstract

Some recent work has shown that newly learned motor skills can symmetrically generalise to the untrained hand (from right to left hand or vice versa), both immediately as well as after a period of 24 hours of learning. However, the neural substrate underlying this form of generalisation after skill memory has stabilized (following 24hrs) is unclear. Trained primary motor cortex (M1) is considered a key site for skill learning-related neuroplastic changes and skill memory stabilization. We hypothesised that trained M1 plays a critical role (as compared to untrained M1) for intermanual skill transfer. We tested 32 young right-handed participants who learned a novel motor skill on Day 1 with their right hand (training session), following which they received offline 1 Hz repetitive transcranial magnetic stimulation (rTMS) over either trained M1 (T-Group) or untrained M1 (U-Group). The skill task consisted of reaching movements from a start circle to one of the eight target circles that appeared on the screen. Participants were instructed to make fast and accurate movements to the target. After each movement, participants received performance feedback. In addition, we applied single pulses TMS to elicit Motor Evoked Potentials (MEPs) in the right hand (T-Group) or in the left hand (U-Group), pre and post learning, as well as immediately, at 5 min and 10 mins post rTMS, allowing us to assess changes in corticospinal excitability, associated with learning and rTMS intervention respectively. On Day 2, all participants were tested for intermanual skill transfer by performing the task with their untrained hand (left hand), as well as for intramanual retention by performing the task with their trained hand (right hand). We found that on Day 1, the two groups learned the task in a similar way (significant Session effect p<0.001; but no significant Group or Group*Block effect). On Day 2, we found a significant Session*Group effect (p=0.04), wherein we noted a significant difference between the two groups on block 1 (p=0.02), indicating that intermanual skill transfer was impaired following rTMS over trained M1 in the T-Group. We didn’t find any significant difference between the last block of learning and the first block of retention indicating a strong retention in both groups. MEPs data did not reveal any significant effect of learning or rTMS (except at 10 min post-rTMS). Our results show that trained M1 (compared to untrained M1) plays an important role in intermanual transfer of a newly learned motor skill, as revealed by the impaired performance at the beginning of the transfer test (on block 1) in the T-Group. Other neural substrates that may mediate motor skill transfer in humans should be explored in future work.