Alexander Maier, Christopher Aura, David Leopold; Visual awareness correlates with layer-specific activity in primary visual cortex. Journal of Vision 2009;9(8):261. doi: 10.1167/9.8.261.
Whether or not activity in the primary visual cortex (V1) is directly related to the visibility of a stimulus is a long-standing debate. To investigate the basis of existing discrepancies in the literature, we measured the BOLD response, along with laminar electrophysiological signals, in area V1 of two behaving monkeys, and correlated responses there with the perceived visibility of a salient stimulus.
We show that stimulus visibility can be reliably derived from the fMRI signal, but not from neuronal spiking activity. We further demonstrate by laminar sampling of V1 local field potentials (LFP) that there is an uneven distribution of percept-related current changes between the different cortical laminae.
Thus, we show that fMRI and neurophysiological signals, while generally in good agreement, become uncoupled during perceptual suppression. Furthermore, our data reveals that if a visual stimulus goes unperceived, there is a drop in the membrane currents in the upper layers of V1.
Work was supported by the Intramural Program of NIH.