Effect of Electrical Stimulus Intensity to Hemodynamic Responses of Somatosensory cortex

To investigate the relationships between neuronal activity and hemodynamics, regional changes of hemoglobin concentration associated with cortical activation in the primary somatosensory cortex (SI) to the electrical stimulation were investigated by near-infrared spectroscopy (NIRS). We measured the hemodynamic evoked responses to the electrical stimuli of some intensities applied on the right thumb. NIRS measurements were performed on 3 healthy right-handed volunteers and we investigated the spatial and temporal features and the magnitude of the optical signal induced by cerebral activation. In this study, we consistently found that an increase in the cerebral concentration of oxygenated hemoglobin [oxy-Hb], and that a decrease in the cerebral concentration of deoxygenated hemoglobin [deoxy-Hb] at somatosensory area. Moreover, as the intensity of electrical stimuli changes stronger from 3 times to 6 times intensity of the sensory threshold of thumb, the increment of [oxy-Hb] and [total-Hb] are augmented.