Dissociation of Stimulus-lnduced Responses in Regional Cerebral Blood Flow and Blood Volume in the Visual Cortex of Humans

Abstract

To elucidate hemodynamic response in the human visual cortex during visual stimulation, changes in regional cerebral blood flow (rCBF) and cerebral blood volume (rCBV) were investigated using blood oxygenation-level dependent (BOLD) and flow sensitive alternating inversion recovery (FAIR) functional magnetic resonance imaging (BOLD- and FAIR-fMRI) and I6-channel near-infrared optical imaging (NIOI) techniques. A white and black annular checherboard (visual angle: 1.2 to 5.8 degrees) focused on perimacular annulus stimulation of the retina, whose temporal frequencies were 0.5, 1.4, 4.7 and 14 Hz with a central fixation point and gray background, was used as the visual stimulus for perimacular annulus. The stimulus-induced activation area obtained with NIOI corresponded to the one measured with BOLD-fMRI. Nevertheless, a dissociation of stimulus induced responses between the BOLD-fMRI signal and hemoglobin (Hb) parameters obtained with NIOI was found; i.e., changes in BOLD-fMRI signal showed a maximal increase at a temporal frequency of l.4-4.7 Hz, while increases in oxygenated (oxy-Hb) and total hemoglobin (total-Hb) concentrations showed a minimum around the same frequency, and deoxygenated hemoglobin (deoxy-Hb) showed a slight but significant decrease. This dissociation of stimulus-induced responses of the BOLD-fMRI signal and Hb parameters could be simulated as a functions of concentration changes in oxy-Hb, deoxy-Hb, and total-Hb. The temporal frequency dependence of changes in rCBF, estimated from FAIR signal and from the time-course change in total-Hb, was similar to that of the BOLD-fMRI signal change. The present results indicated that stimulus-induced responses of rCBF were dissociated from those of rCBV in the visual cortex of humans during perimacular stimulation at temporal frequency around 1.4-4.7 Hz.