Rapid alternation of conscious and suppressed stimulus representations in the primate brain

gist

A bioRxiv preprint by Janis Hesse, Doris Tsao and colleagues finds macaque cortex switches about 15 times a second between seen and suppressed images. They recorded with Neuropixels probes in face patches of inferotemporal and prefrontal cortex in two monkeys during binocular flash suppression, where one eye's image is seen and the other eye's image stays hidden from awareness. Faces reconstructed from each brief state matched either the seen or the suppressed face. Averaging over both states explains why earlier studies found only weak perceptual modulation. The preprint has not been peer reviewed.

ideas

• Population activity alternates within single trials. A hidden Markov model, which infers switching between unobserved states, put median state dwell times at 64 ms and 59 ms, while perceptual switches in binocular rivalry run at about 0.5 Hz.
• Each state carries a near-pure representation of one face. In state 1, reconstruction of the conscious face reached over 80% explained variance for some features against a ceiling above 90% from unambiguous viewing, while the suppressed face fell to chance, and state 2 reversed the pattern.
• The same neurons switch, and the conscious state has higher gain. Across 543 cells, tuning gain for the conscious face in state 1 averaged 1.21 times the gain for the suppressed face in state 2, and a linear decoder separated the states with 66% accuracy.
• Controls leave only a coordinated two-state model. The results survived split-half cross-validation, trial balancing and a shuffled-template control, and simulated averaging, conscious-only and uncoordinated models each failed at least three of four tests.
• Prefrontal cortex interleaves the same way. Orbitofrontal and ventrolateral prefrontal recordings reproduced the alternation with lower reconstruction quality, while state switching across the ML and AM face patches of inferotemporal cortex showed little coordination.

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