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Abstract

Previously we demonstrated that the negative BOLD response (NBR) in non-stimulated regions of V1 is associated with decreases in neuronal activity (DsiNA), and that the DsiNA cannot be caused by hypoxia due to the associated negative cerebral blood flow (CBF) response. DsiNA were observed 11 mm away from the stimulated region; thus they cannot be exclusively mediated by the horizontal connections.
Aims
1) Are the NBR and DsiNA independent or coupled phenomena?
2) Does the NBR reflect decreases in synaptic or in spiking activity?
Monkeys were stimulated visually with rotating checkers. Electrical recordings were obtained simultaneously with fMRI.
Peripheral visual-field (VF) stimuli elicited PosBR/NBR in peripheral/more central VF representations in V1. The amplitude of the NBR measured across single trials was correlated with the corresponding amplitude of the DsiNA within single sessions (p<0.0001). The NBR was correlated with the amplitudes of decreases in the comprehensive neuronal signal, LFP, MUA, and action potentials (APs) of single neurons. As expected, the variance of the time course of the PosBR could be better predicted by the variance of the LFP (r2=.69±.15, n=5 sessions) than by that of the MUA (r2=.57±.22) and the APs (r2=.52±.22). In contrast, the variance of the NBR could be comparably predicted using the decreases in LFP (r2=.59±.17), MUA (r2=.64±.10) or APs (r2=.60±.11). Similar DsiNA were observed outside of the scanner, ruling out the possibility of artifacts caused by electrical recordings simultaneously with fMRI.
Conclusions
1) Non-stimulated regions adjacent to active regions in V1 decrease their neuronal activity.
2) The comparable decreases in LFP, MUA and APs are consistent with decreases in the input to the NBR region and/or suppression within the NBR region.
3) The findings corroborate a model in which the DsiNA trigger reductions in CBF that contribute significantly to the NBR.