Supplementary motor area enhanced hemodynamic responses to loading after inhibitory cTBS

Large-extent movements (LEMs) are vital for daily activities, and their recovery remains a challenge in neurorehabilitation due to inevitable loading on muscles. Since inhibitory cTBS may facilitate recovery but also disrupt task control, we ask whether a previously identified linear relationship between load and cortical activation would retain, after cTBS over the contralateral supplementary motor area (SMA). It will set a benchmark for choosing resistance during brain stimulation. Hemodynamic activities of SMA and M1 during LEMs were monitored by functional Near-Infrared Spectroscopy (fNIRS) in this study. Twelve healthy participants received 40s of cTBS over SMA, before and after which the participants were instructed to complete LEMs with varying loads (0, 3, and 15 pounds) repetitively. When lifting 0-pound and 3-pound weights, the β of the left SMA and M1 increased significantly after cTBS (p < 0.05). Also, the random intercepts of individual subjects increased significantly in the left SMA, left M1, and right SMA, but the slopes were not significantly affected by cTBS. Data also showed a significant positive correlation between the intercept of left M1, right SMA&M1 areas and age (all p < 0.05). Despite cTBS-induced inhibition, the supplementary motor area (SMA) exhibited enhanced fNIRS responses to increased loads, and the positive correlation between load inertia and motor-cortical activation remained unaltered.