The effects of transcranial stimulation on paretic lower limb motor excitability during walking

Balanced transcallosal inhibition sustains symmetrical corticomotor excitability and assists the performance of bimanual voluntary movements. After stroke, transcallosal inhibition becomes asymmetric. This finding raised the notion that reducing poststroke asymmetry in transcallosal inhibition might prime the motor system before training and lead to improvements in walking recovery. In this study, we examined three neuromodulatory protocols applied during walking to determine if they could increase ipsilesional and decrease contralesional motor excitability in patients with chronic stroke. Inhibitory repetitive transcranial magnetic stimulation and inhibitory paired associative stimulation were applied to the contralesional motor system, and facilitatory anodal transcranial direct current stimulation was applied to the ipsilesional motor system. We tested the bilateral modulatory effects of each stimulation protocol on the tibialis anterior, medial gastrocnemius, medial hamstrings, and vastus lateralis of nine patients with chronic stroke. All stimulation protocols increased paretic limb and decreased nonparetic limb motor excitability. There was no statistical difference in the extent of modulation between these stimulation protocols. This result suggests these three protocols are promising candidate priming mechanisms for testing the hypothesis in a future study that reducing the poststroke asymmetry of between-hemisphere motor excitability will enhance the effect of gait therapy.