We investigated BOLD responses along the rat visual pathway via inter-stimulus-intervals (ISI) and stimulus pulse width (PW) modulation. PWs did not impact negative BOLD responses (NBRs) while shortening ISI resulted in very large increases in NBRs. Visual cortex (VC) NBRs at short ISIs were accompanied by decreased positive BOLD responses (PBRs) in lateral geniculate nucleus of the thalamus (LGN) and superior colliculus (SC). At the shortest ISI (30ms) NBRs were observed in SC. Along with reported reduced visual evoked potentials amplitude at short ISIs, our findings suggest decreased net excitability as a source for negative BOLD responses in this scenario.
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