Modulatory Effect of Peripheral Magnetic and Neuromuscular Electrical Stimulation on Cortical Excitability: A Functional Near-Infrared Spectroscopy Study

Abstract Background : The present study was designed to investigate the effects of neuromuscular electrical stimulation (NMES) and peripheral magnetic stimulation (PMS) applied to the wrist extensor muscle on the cortical activity of healthy adults by using fNIRS. Methods : Fifteen healthy adult subjects (7 males, mean age: 27.13 ± 4.52 years) all received two different conditions of peripheral muscle stimulation in random order: (1) NMES and (2) PMS. The sessions were separated by at least 48 h as a washout period. During muscle stimulation, the motor evoked potential (MEP) of the left primary motor cortex (M1) was measured by transcranial magnetic stimulation (TMS) and the concentration of oxygenated (HbO) and deoxygenated (HbR) hemoglobin detected by fNIRS were used to evaluate the excitability and the activity of the cortex. Results : After the stimulation of the wrist extensor, the MEP amplitude in the left M1 area did not change in both conditions, and there was no difference between NMES and PMS condition. NMES reduced HbO values of several channels in the Prefrontal cortex (PFC), Somatosensory motor cortex (SMC) and Occipital cortex (OC), and HbR valus of several channels in the PFC and SMC. During the PMS stimulation period, the HbO value of all brain areas did not change significantly, while the HbR value of the SMC area decreased. The HbO and HbR value of the channels in the SMC did not differ between NMES and PMS. Inter-region of interest and inter-channel analysis between NMES and PMS showed no difference in functional connectivity. Conclusions : In the case of wrist extensor muscle stimulation, both NMES and PMS can induce cortical activation. PMS targeted to increases the activity of the contralateral SMC, while NMES increased contralateral SMC activity and negatively activated the PFC and OC.