Divergence of fMRI and neural signals in V1 during perceptual suppression in the awake monkey

Abstract

Primary visual cortex (V1) activation in humans is attenuated during perceptual suppression, but recordings of single neurons in monkey V1 show little suppression. The authors resolve this apparent conflict, finding that perceptual suppression in monkeys is associated with strong suppression of population level activation, but only weak suppression of single neuron activity. The role of primary visual cortex (V1) in determining the contents of perception is controversial. Human functional magnetic resonance imaging (fMRI) studies of perceptual suppression have revealed a robust drop in V1 activity when a stimulus is subjectively invisible. In contrast, monkey single-unit recordings have failed to demonstrate such perception-locked changes in V1. To investigate the basis of this discrepancy, we measured both the blood oxygen level–dependent (BOLD) response and several electrophysiological signals in two behaving monkeys. We found that all signals were in good agreement during conventional stimulus presentation, showing strong visual modulation to presentation and removal of a stimulus. During perceptual suppression, however, only the BOLD response and the low-frequency local field potential (LFP) power showed decreases, whereas the spiking and high-frequency LFP power were unaffected. These results demonstrate that the coupling between the BOLD and electrophysiological signals in V1 is context dependent, with a marked dissociation occurring during perceptual suppression.