LAUSR

Introduction Prism adaptation is a form of sensorimotor learning where participants have to regain normal pointing accuracy under circumstances where their entire visual field is shifted to one side by prism glasses. Once the goggles are removed, prism aftereffects are expressed as pointing errors in the direction opposite to that of the prismatic shift. When coupled with prism adaptation, anodal transcranial direct current stimulation (a-tDCS) to the primary motor cortex (M1) increases retention of prism aftereffects in healthy participants. However, the mechanisms by which this motor memory boost occurs remain largely unknown. Objectives We sought to investigate the brain mechanisms underlying stimulation-enhanced motor memory by examining how inter-individual differences in neurochemical and functional response to a-tDCS relate to inter-individual differences in its effect on prism aftereffects. Materials and methods Participants underwent two MR scanning sessions during which they either received sham or real a-tDCS to M1. We used Magnetic Resonance Spectroscopy (MRS) and resting state functional Magnetic Resonance Imaging (rs-fMRI) to characterise individuals’ neurochemical and functional response to a-tDCS ( Bachtiar et al., 2015 , Stagg et al., 2009 ). Participants also underwent two behavioural sessions during which prism adaptation was either combined with sham or real a-tDCS. Results Preliminary results suggest that the bigger the reduction in GABA concentration in M1 following a-tDCS, the stronger the effect of a-tDCS on the retention of prism aftereffects. Conclusion This result supports the idea that the effect of anodal tDCS on motor memory depends on its effect on the GABAergic system. Further analyses will also consider the influence of the a-tDCS induced changes in functional connectivity within the motor network.