Decoding rapidly presented visual stimuli from prefrontal ensembles without report nor post-perceptual processing

Abstract

The role of the primate prefrontal cortex (PFC) in conscious perception is debated. The global neuronal workspace theory of consciousness predicts that PFC neurons should contain a detailed code of the current conscious contents. Previous research showed that PFC is indeed activated in paradigms of conscious visual perception, including no-report paradigms where no voluntary behavioral report of the percept is given, thus avoiding a conflation of signals related to visual consciousness with signals related to the report. Still, it has been argued that prefrontal modulation could reflect post-perceptual processes that may be present even in the absence of report, such as thinking about the perceived stimulus, therefore reflecting a consequence rather than a direct correlate of conscious experience. Here, we investigate these issues by recording neuronal ensemble activity from the macaque ventrolateral PFC during briefly presented visual stimuli, either in isolated trials in which stimuli were clearly perceived or in sequences of rapid serial visual presentation (RSVP) in which perception and post-perceptual processing were challenged. We report that the identity of each stimulus could be decoded from PFC population activity even in the RSVP condition. The first visual signals could be detected at 60 ms after stimulus onset and information was maximal at 150 ms. However, in the RSVP condition, 200 ms after the onset of a stimulus, the decoding accuracy quickly dropped to chance level and the next stimulus started to be decodable. Interestingly, decoding in the ventrolateral PFC was stronger compared to posterior parietal cortex for both isolated and RSVP stimuli. These results indicate that neuronal populations in the macaque PFC reliably encode visual stimuli even under conditions that have been shown to challenge conscious perception and/or substantially reduce the probability of post-perceptual processing in humans. We discuss whether the observed activation reflects conscious access, phenomenal consciousness, or merely a preconscious bottom-up wave.

A mesoscale connectome-based model of conscious access in the macaque monkey

“…However, in our dynamical model the late activity reaches its peak in prefrontal cortex after 200ms (see Fig 2B). This broadly matches the timing of stimulus-induced prefrontal activity observed in monkey experiments, which is observable from ∼60 ms following stimulus onset and peaks after ∼150−200 ms (Bellet et al 2022; Thorpe and Fabre-Thorpe 2001; Van Vugt et al 2018). Therefore, our connectome-based dynamical model accounts for the temporal progression of activity states observed in the brain during stimulus detection tasks.…”

Theories of consciousness

“…Using a variety of experimental paradigms, many neuroimaging studies have found prefrontal engagement for conscious (versus unconscious) perception 48 , based on both regional activity 100,101 and on functional connectivity between frontal and other regions 102 . A small number of primate studies have also found that conscious contents can be decoded from prefrontal activity patterns during binocular rivalry, continuous flash suppression, and rapid serial presentation of visual stimuli [103][104][105] ; see also REF. 106 for a more complex picture in which content-relevant information was decoded from a wide range of both activated and deactivated cortical regions during an object recognition task.…”

Representing experience over time: sustained sensory patterns and transient frontroparietal patterns

“…However, unlike pure no-report paradigms, here the subjects had to decide whether the stimulus belonged to a target category or not, implying that our findings may still be related to task requirements. Nevertheless, our findings are unique in showing stimulus specific representations which are not mapped to task distinctions (see recent findings in monkeys in 82,83 ). That is, we find highly accurate decoding between image categories that are both non-targets, and which do not share any low-level properties with the target stimuli (e.g., face and watches).…”