Beta to low-gamma rhythmic brain stimulation over primary motor cortex and supplementary motor area differentially...

Non-invasive brain stimulation such as transcranial direct current stimulation over the primary motor cortex (M1) and supplementary motor area (SMA) during gait can positively affect gait ability in patients after stroke; however, the frequency-specific modulatory effects of rhythmic brain stimulation over the M1 and SMA on the oscillatory neural drives during gait remain unclear. Therefore, we investigated the effects of the alpha and beta to low-gamma oscillatory transcranial direct current stimulation (otDCS) over the M1 and SMA on the oscillatory neural drives to lower limb muscles during gait, using coherence analysis of paired surface electromyography, in 32 healthy young adults. Experiments involved treadmill gait measurements, comprising pre-stimulation gait, gait with otDCS in three stimulation conditions (10-Hz otDCS, 30-Hz otDCS, and sham stimulation) over the M1 and SMA, and post-stimulation gait. Although the 10-Hz otDCS and sham stimulation induced no effects, the 30-Hz otDCS over the M1 and SMA significantly increased the average values of the tibialis anterior intramuscular coherence and vastus medialis and lateralis intermuscular coherence, respectively, in the 20-40 Hz (beta to low-gamma) frequency bands during post-stimulation gait compared to the pre-stimulation gait. Therefore, beta to low-gamma otDCS over the M1 and SMA during gait selectively increased the oscillatory neural drives to distal and proximal lower limb muscles, respectively. This study provides novel evidence that beta to low-gamma rhythmic brain stimulation could be an effective rehabilitation strategy for improving gait ability in patients with central nervous system disorders, with specific deficits in the M1 or SMA.