Role of Dorsolateral Prefrontal Cortex During Motor Preparation on Anticipatory Postural Adjustments

Hemodynamic responses in the dorsolateral prefrontal cortex (DLPFC) during gait initiation could influence anticipatory postural adjustments (APAs). However, how DLPFC during motor preparation modulates APA integration remains unknown. Seventeen right-handed participants completed two sessions of the rapid arm raising task and simultaneously received the real and sham repetitive transcranial magnetic stimulation (rTMS) over the left DLPFC during the motor preparation period before arm raising. The rTMS protocol involves 10 Hz stimulation at an intensity of 110% of the resting motor threshold. The activations of DLPFC, supplementary motor area (SMA), and primary motor cortex (M1) were recorded using the functional near-infrared spectroscopy (fNIRS) during the rapid arm raising task. The APAs were assessed by recording the latency and amplitude of the postural muscles using the surface electromyography. Compared with sham stimulation, the activation of DLPFC (t = -2.97, p = 0.033), SMA (t = -2.141, p = 0.048) and M1 (t = -2.787, p = 0.013) was significantly decreased during real rTMS. It was also observed that the latency was reduced (t = -2.209, p = 0.041) and the amplitude was decreased (t = -2.696, p = 0.010) during real rTMS in the superficial lumbar multifidus. The DLPFC activation was positively correlated with those of M1 (r = 0.569, p = 0.017) and SMA (r = 0.595, p = 0.012) in the real rTMS session. Finally, the oxygenated hemoglobin concentration in the DLPFC and M1 significantly correlated with the muscle amplitude (r = 0.646, p = 0.007 and r = 0.589, p = 0.013, respectively). The association between DLPFC and the APAs was totally mediated by M1. rTMS over the DLPFC during motor preparation could enhance the neural efficiency of the M1, and subsequently facilitate the integration of APAs with voluntary movement.