Background: Recovery of motor function after stroke may depend on a balance of activity in the neural network involving the affected and the unaffected motor cortices.
Objective: To assess whether transcranial direct current stimulation (tDCS) can increase the training-induced recovery of motor functions.
Methods: In an exploratory study, 14 patients with chronic stroke and mean Fugl-Meyer Upper Extremity Motor Assessment of 29 (range = 8-50) entered a double-blind sham-controlled study, aimed to investigate neurophysiological and behavioral effects of bihemispheric tDCS (cathodal stimulation of the unaffected motor cortex and anodal stimulation of the affected motor cortex), combined with constraint-induced movement therapy (CIMT).
Results: Patients in both groups demonstrated gains on primary outcome measures, that is, Jebsen Taylor Hand Function Test, Handgrip Strength, Motor Activity Log Scale, and Fugl-Meyer Motor Score. Gains were larger in the active tDCS group. Neurophysiological measurements showed a reduction in transcallosal inhibition from the intact to the affected hemisphere and increased corticospinal excitability in the affected hemisphere only in the active tDCS/CIMT group. Such neurophysiological changes correlated with the magnitude of the behavioral gains. Both groups showed a reduction in corticospinal excitability of the unaffected hemisphere.
Conclusions: CIMT alone appears effective in modulating local excitability but not in removing the imbalance in transcallosal inhibition. Bihemispheric tDCS may achieve this goal and foster greater functional recovery.