Initial-dip based identification of the brain area for right-hand finger movement

In this paper, we have used a linear combination of three gamma functions to estimate the location of cortical activation during right-hand thumb finger (RHTF) flexion/extension using functional near-infrared spectroscopy (fNIRS). The three gamma functions are used to model the initial dip, conventional hemodynamic response, and undershoot of oxy-hemoglobin signals. The brain signals of five healthy subjects during RHTF flexion/extension task are acquired from the motor cortex. Vector phase analysis with a threshold circle as a decision criterion is used to ensure the presence of initial dips in fNIRS signals. The results show that the brain area around C3 during the RHTF flexion/extension task becomes highly activated for all subjects. Also, the t-map generated for the initial period, i.e., 2.5 sec, is more spatially localized than the t-map drawn for 15 sec period. The result demonstrated that the model obtained using the linear combination of three gamma functions can identify the initial dip brain region for motor activity task.