Gait-combined transcranial alternating current stimulation modulates cortical control of muscle activities during gait.

ABSTRACT

Non-invasive brain stimulation has been of interest as a therapeutic tool to modulate cortical excitability. However, there is little evidence that oscillatory brain stimulation can modulate the cortical control of muscle activities during gait, which can be assessed using coherence analysis of paired surface electromyographic (EMG) recordings. This study aimed to investigate the effects of gait-combined transcranial alternating current stimulation (tACS) at the gait cycle frequency on the cortical control of muscle activities during gait using EMG-EMG coherence analysis. Fourteen healthy young adults participated in this study. All participants underwent 2 test conditions (real tACS and sham stimulation over the leg area of the primary motor cortex during 10-min treadmill walking). The average peak-to-peak amplitudes of the motor evoked potentials (MEPs) from the tibialis anterior (TA) and lateral gastrocnemius muscles in the sitting position and EMG-EMG coherences in the TA muscle, triceps surae muscles, quadriceps muscles, and hamstring muscles during gait were measured before and after stimulation. Entrainment effect was significantly higher during real tACS than during sham stimulation. After real tACS, the MEP amplitude and beta band (13-33 Hz) coherence area increased in the TA muscle. The change in MEP amplitude from the TA muscle was positively correlated with the change in beta band coherence area in the TA muscle. Gait-combined tACS can modulate the strength of descending neural drive to TA motoneurons during gait. This suggests that oscillatory brain stimulation is a useful therapeutic tool to modulate the cortical control of muscle activities during gait.