Quantification of delayed oxygenation in ipsilateral primary motor cortex compared with contralateral side during a unimanual dominant-hand motor task using near-infrared spectroscopy.

Using near-infrared spectroscopy (NIRS) techniques, it is possible to examine bilateral motor cortex oxygenation during a static motor task. Cortical activation was assumed to be reflected by increased oxygenation. The purpose of the present study was to examine the time course of oxygenation in the bilateral motor cortex during a low-intensity handgrip task. Six healthy, right-handed subjects participated in the study. The near-infrared spectroscopy probes positioned over the bilateral motor cortex were used to measure the cortical activation throughout a handgrip task carried out. The subjects performed a 3-min handgrip task with increasing intensity in a ramp-like manner [10-30% of the maximal voluntary contraction (MVC) at 6.67% MVC.min(-1)]. Contralateral motor cortex oxygenation increased significantly from 100 to 180 s after the start of the motor task compared with the baseline value (p<0.05). Ipsilateral motor cortex oxygenation also increased significantly from 130 to 180 s after the start of the motor task (p<0.05). The onset of increase in oxyhemoglobin ([HbO2]) and decrease in deoxyhemoglobin ([Hb]) in contralateral motor cortex area (M1) were significantly earlier than in ipsilateral M1 (respectively, p<0.05). These results show that there is a delayed oxygenation in ipsilateral primary motor cortex area compared with contralateral side during a unimanual dominant-hand motor task.