Modulating primary motor cortical excitability and facilitating sensorimotor skill learning with reversed visual input

Abstract

It is currently unknown, whether visual input can not only improve behavioural performance in the untrained hand, but also produce bihemispheric, plastic changes in the human primary motor cortex (M1). Here, we used transcranial magnetic stimulation (TMS) to test whether skill acquisition with reversed vision modulates M1 plasticity in three different conditions before and after training on a 30-minute serial reaction-time task (SRTT) in 21 healthy humans. Training interventions included: (1) viewing the ‘mirrored’ image of the moving right-hand superimposed over the inactive left-hand with left-right optical reversing spectacles (Prism Group); (2) directly viewing the active learning right-hand (Direct Vision Group); and (3) viewing an image of the moving left-hand while both hands remained inactive (Action Observation Group). Post-training results indicated that reaction time in the SRTT decreased in the untrained left-hand only in the Prism (p = 0.02) and Action Observation (p = 0.03) groups. Training with direct vision resulted in increased M1 excitability in the trained, left hemisphere (all p-values < 0.003), but no changes in M1 excitability in the untrained, right hemisphere.  In contrast, training with the reversal of visual input induced the opposite pattern on M1 excitability: increase in the right hemisphere (p = 0.04) and no changes in the left hemisphere.  Interactions between right ventral premotor and ipsilateral motor cortex at rest were modified after learning with reversed vision (p = 0.04).  Action observation induced excitability changes in both hemispheres (all p-values < 0.03). This suggests the importance of visual input in modulating M1 plasticity. 

Acknowledgments: This research was supported by grants from the Mitacs-Accelerate Internship and Natural Sciences and Engineering Research Council of Canada (NSERC). M. Vesia was supported by post-doctoral fellowships from the Ontario Ministry of Research and Innovation and Heart and Stroke Foundation of Ontario Centre for Stroke Recovery.