Abstract: Near-infrared spectroscopy (NIRS) is employed to examine the neuronal activity and vascular response of a peripheral nerve for research or clinical purposes. An embodiment for implementing this approach has: a nerve stimulator; a tissue spectrometer; a stimulation probe adapted to apply a stimulation from the nerve stimulator to a peripheral nerve; at least one illumination optical fiber, where each illumination optical fiber is adapted to transmit a near-infrared source light to the peripheral nerve after the stimulation is applied; and a detection optical fiber adapted to collect and deliver to the tissue spectrometer a returning light from the peripheral nerve after each source light is transmitted to the peripheral nerve. The returning light has a returning intensity, and the tissue spectrometer can determine the returning intensity to provide readings of optical diffuse reflectance of the peripheral nerve after the stimulation is applied.