Abstract
Using near-infrared spectroscopy, we studied cerebral hemodynamic responses to electric median nerve stimulation in ten subjects. The recordings were conducted by optical fibers placed over the left scalp. Electric stimuli were delivered to contra- and ipsilateral median nerves, respectively. Hemodynamic responses in the secondary somatosensory cortex were observed following each median nerve stimulation, except for three drowsy subjects. The contralateral stimulation tended to induce a larger response. The degree of change in oxygenated hemoglobin was hardly related to stimulus intensities, and was augmented by attention. Four subjects showed long-lasting responses throughout the stimulus periods, while three other subjects revealed transient responses. Thus, taking account of the temporal activation patterns is necessary for proper interpretation of the hemodynamic response following electric nerve stimulation.
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