The data from the seven participants were unambiguous. Paying attention to the target consistently and strongly increased the fMRI activity, regardless of whether the subject saw the target or not. This result was expected because many previous studies had shown that attending to a signal reinforces its representation in the cortex. Much more intriguing, though, was that whether or not the stimulus was consciously perceived made no difference to signal strength. Visibility didn’t matter to V1; what did was whether or not selective visual attention focused on the grating. Indeed, the experimentalists could not decode from the signal whether or not the subject saw the stimulus.
I am very pleased by their finding because it is fully in line with the hypothesis that Nobel laureate Francis Crick and I advanced in 1995. Writing in Nature, we had argued that neurons in V1 do not directly contribute to visual consciousness. Our speculation was based on the absence of a direct connection between cells in V1 and their partners in the frontal lobe in macaques. The fMRI experiment described here provided evidence for our conjecture. Whether or not our connectional argument is valid remains open, of course.
It appears that the habitat of consciousness is not the cortical region at the bottom of the extended hierarchy of cortical areas dedicated to vision. Consciousness is restricted to higher regions, possibly those that are engaged in a reciprocal, two-way communication with the prefrontal cortex, the seat of planning.
The history of any scientific concept—energy, atom, gene, cancer, memory—is one of increased differentiation and sophistication until it can be explained in a quantitative and mechanistic manner at a lower, more elemental level. These and related experiments put paid to the notion that consciousness and attention are the same. They are not, and the brain responds differently to them. This distinction clears the decks for a concerted, neurobiological attack on the core problem of identifying the necessary causes of consciousness in the brain.
This article was originally published with the title Consciousness Does Not Reside Here.