Immediate and late modulation of interhemipheric imbalance with bilateral transcranial direct current stimulation in acute stroke

BACKGROUND: Significant changes in neurophysiological and clinical outcomes in chronic stroke had been reported after tDCS; but there is a paucity of data in acute stroke. OBJECTIVE: We aimed to evaluate whether a tDCS-induced modulation of primary motor cortex excitability in patients with acute stroke enhances motor recovery associated with rehabilitation and induces differential neuroplasticity. METHODS: We conducted two experiments in acute stroke patients. In experiment 1 (14 patients), we tested the immediate effects of bilateral tDCS alone as compared to sham tDCS on recovery. Experiment 2 (20 patients) was designed to assess effects of bilateral tDCS delivered together with constraint-induced movement therapy (CIMT). In this experiment, we included a longer follow-up (3 months) and measured, in addition to the same clinical outcomes of experiment 1, changes of motor cortex excitability and the amount of promoted LTP-like activity. RESULTS: Despite the expected improvement at 1 week, none of the clinical measures showed any different modulation in dependence of CIMT and tDCS. On the neurophysiological assessments, on the other hand, the Real_tDCS group, compared to Sham_tDCS group, showed a reduction of inter-hemispheric imbalance when considering the differences of motor evoked potential between both 3-month and 1 week follow up (P = 0.007) and three month and baseline (P = 0.015). CONCLUSIONS: Despite the lack of additional clinical changes, real bilateral tDCS, together with CIMT, significantly reduces inter-hemispheric imbalance between affected and unaffected hemispheres. These findings may shed light on plasticity changes in acute stroke and its potential impact in chronic phases