We discovered something totally unexpected about the neural structure of consciousness that overturns decades of thinking on its biological basis and brings us significantly closer to the recipe for generating conscious awareness. New preprint: biorxiv.org/content/10.648…

TL/DR: We found neural activity across both inferotemporal and prefrontal cortex alternates between a conscious mode and an unconscious mode ~ 15 times every second.

Bistable illusions like the face-vase illusion provide a powerful window into consciousness. They suggest that conscious awareness is the result of an active process in which the brain selects one interpretation to reach awareness out of all possible ones.

To study how this works, we used binocular flash suppression: in this paradigm, two different images are shown to the left and right eyes, and we can fully control which image is consciously perceived and which remains unconscious.

We recorded responses from thousands of neurons in inferotemporal and prefrontal cortex using Neuropixels probes while presenting thousands of flash suppression stimulus pairs. We found that neural activity rapidly alternates between two coordinated states.

Remarkably, when we reconstructed the image using neural activity from one of the states, it looked exactly like the conscious face, and when we did the same from the other half of time, it looked exactly like the suppressed face. This means that just from neural activity, we can reconstruct in rich detail not only something that you consciously perceive, but also something that escapes your awareness.

These findings show that representation of conscious and suppressed content alternates every ~ 60 ms. Thus conscious perception does not reside in a specific brain region, but rather a specific temporal phase.

At the single-neuron level, we found that cells concertedly switched their tuning every 60 ms, from representing the conscious face to the suppressed face. Thus the same population of neurons represent both what you’re aware of and what you’re not, at different moments of time.

Personal note: For almost a decade, Janis Hesse and I have been struggling to resolve the discrepancy between the classic story reported in textbooks that anterior parts of the brain contain a pure representation of conscious awareness, and the reality that the neurons Janis recorded from simply didn’t reflect this: modulation by conscious awareness during rivalry was stubbornly weak.

This raised a gnawing puzzle: how could the neural correlate of consciousness appear so weak everywhere we looked, when conscious perception during rivalry is so clear? We were trapped in our expectations. But the brain didn't care.

So I had to jump for joy when Janis showed me the reconstructions. At last, we had found a pure correlate of conscious awareness in the brain during rivalry that matched the clarity of conscious perception. He had solved the puzzle. And once again, the truth is always the most interesting.

What is most exciting is that we have uncovered a signal deep in the brain that richly represents a stimulus you’re not aware of. This finding, in my opinion, makes it tractable to understand how a pattern of neural activity accesses consciousness. The previous dominant idea--that suppressed stimuli become progressively weaker as you go anterior (“fail to ignite”)--left the question of how a representation becomes consciously accessible extremely hard to pin down. Whereas now, with whoppingly clear signals corresponding to both what is and isn’t conscious, we can follow both sets of footprints, to track down the full machinery for generating conscious percepts.