The oxygen saturation in the primary motor cortex during a single hand movement: functional near-infrared spectroscopy (fNIRS) study

Functional near-infrared spectroscopy is a noninvasive optical imaging technique to register brain activity. It utilizes near-infrared light to evaluate the oxygenated (HbO) and deoxygenated hemoglobin concentration. Here, we used HbO and HbR to analyze the oxygen saturation and electromyographic signals to study muscle activity during the single left- and right-hand movements. Sixteen right-handed volunteers participated in the experiment. During the active phase of the experiment, the subject was asked to perform movements with his left or right hand according to the screen instructions. There were 40 total hand movement trials (20 for each hand) that were performed in random order. The oxygen saturation increased contralaterally, peaking at about 6 s post-command onset and then decreased, reaching baseline level at 12 s. The maximal amplitudes appeared in the primary motor (M1) cortex in the hemisphere contralateral to the performing limb. In the left hemisphere, the right hand induced a higher response than the left hand. In the right hemisphere, the response amplitude remains similar for both hands. We hypothesized that the right hand being a dominant hand in the group may require additional neuronal recruitment in the contralateral M1 cortex.