Near-infrared study of fluctuations in cerebral hemodynamics during rest and motor stimulation: Temporal analysis and spatial mapping

We have noninvasively studied the motor cortex hemodynamics in human subjec ts under rest and motor stimulation conditions using a multichannel near-in frared tissue spectrometer. Our instrument measures optical maps of the cer ebral cortex at two wavelengths (758 and 830 nm), with an acquisition time of 160 ms per map. We obtained optical maps of oxy- and deoxy-hemoglobin co ncentration changes in terms of amplitudes of folding average, power spectr um and coherence at the stimulation repetition frequency, and the phase syn chronization index. Under periodic motor stimulation conditions, we observe d coherence and frequency or phase synchronization of the local hemodynamic changes with stimulation. Our main findings are the following: (1) The amp litude of the hemodynamic response to the motor stimulation is comparable t o the amplitude of the fluctuations at rest. (2) The spatial patterns of th e oxy- and deoxy-hemoglobin responses to the stimulation are different. (3) The hemodynamic response to stimulation shows a spatial localization and a level of phase synchronization with the motor stimulation that depends on the stimulation period. (C) 2000 American Association of Physicists in Medi cine.