Neural mechanism underlying task-specific enhancement of motor learning by concurrent transcranial direct current stimulation

The optimal protocol for neuromodulation by transcranial direct current stimulation (tDCS) remains unclear. Using rotarod paradigm, we found that mouse motor learning was enhanced by anodal tDCS (3.2 mA/cm2) during but not before or after task performance. Dual-task experiments showed that motor learning enhancement was specific to the task accompanied by concurrent anodal tDCS. Studies using stroke model mice induced by middle cerebral artery occlusion (MCAO) showed that concurrent anodal tDCS restored motor learning capability in a task-specific manner. Transcranial in vivo calcium imaging further showed that anodal and cathodal tDCS elevated and suppressed neuronal activity in the primary motor cortex (M1), respectively. Anodal tDCS specifically promoted the activity of task-related M1 neurons during task performance, suggesting that elevated Hebbian synaptic potentiation in task-activated circuits accounts for motor learning enhancement. Thus, application of tDCS concurrent with the targeted behavioral dysfunction could represent a more effective approach for treating brain disorders.