Optimal Combination of Anodal Transcranial Direct Current Stimulations and Motor Imagery Interventions

Motor imagery contributes to enhance the (re)learning of motor skills through remapping of cortical networks. Combining motor imagery with anodal transcranial direct-current stimulation (a-tDCS) over the primary motor cortex has further been shown to promote its beneficial effects on postural control. Whether motor imagery should be performed concomitantly to a-tDCS (over depolarized membrane) or consecutively (over changing neurotransmitters activity) remains to be elucidated. In the present study, we measured the performance in a postural control task before and after three experimental conditions. Participants received a-tDCS before (tDCS_Before), during (tDCS_During), or both before and during motor imagery training (tDCS_{Before + During}). Performance was improved after tDCS_During, but not after both the tDCS_Before and tDCS_{Before + During} conditions. These results support that homeostatic plasticity is likely to operate following a-tDCS through decreasing cortical excitability and that motor imagery should be performed during anodal stimulation for optimum gains.