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要旨

n a previous fMRI study (Shmuel et al., HBM 2001), a robust sustained negative BOLD response (NBR) and blood flow response was detected in the human occipital cortex. Here we report on a sustained (different from the initial dip) NBR in areas V1, V2, and V3 of the macaque. Anesthetized monkeys were presented in 4 cycles with a rotating polar checker pattern (48 s) followed by a blank gray image (48 s). Fifteen axial slices were imaged (GE-EPI, 4.7 T, 0.750.752 mm, TR=.75 s, 6 s/volume). In response to stimulation at 0-10 eccentricity, a positive BOLD response (PBR) and NBR were observed within the central and peripheral visual representation, respectively. The NBR was found preferentially in gray matter and was spatially reproducible across subjects. The time course of the NBR and PBR (mean amplitude ratio 0.5) were similar, suggesting similar mechanisms. Initial results from simultaneous fMRI and electrophysiology demonstrated NBR in 3 regions where no robust changes in electrical activity occurred. We are currently pursuing additional fMRI-electrophysiology experiments. Discussion 1) Robust NBR exists in the monkey brain. 2) Since the activity in the periphery is not expected to increase, the NBR here is the result of a decrease in blood flow rather than increase in oxygen consumption.