Distinct cortical codes and temporal dynamics for conscious and unconscious percepts

Moti Salti,Simo Monto,Jean-Remi King,Stanislas Dehaene,Lucie Charles,Lauri Parkkonen

doi:10.7554/elife.05652

Abstract

The neural correlates of consciousness are typically sought by comparing the overall brain responses to perceived and unperceived stimuli. However, this comparison may be contaminated by non-specific attention, alerting, performance, and reporting confounds. Here, we pursue a novel approach, tracking the neuronal coding of consciously and unconsciously perceived contents while keeping behavior identical (blindsight). EEG and MEG were recorded while participants reported the spatial location and visibility of a briefly presented target. Multivariate pattern analysis demonstrated that considerable information about spatial location traverses the cortex on blindsight trials, but that starting ≈270 ms post-onset, information unique to consciously perceived stimuli, emerges in superior parietal and superior frontal regions. Conscious access appears characterized by the entry of the perceived stimulus into a series of additional brain processes, each restricted in time, while the failure of conscious access results in the breaking of this chain and a subsequent slow decay of the lingering unconscious activity.

Highlights

The scientific investigation of consciousness divides into two major branches (Koch, 2004; Dehaene et al, 2014)
Previous experiments exploring the signatures of conscious access have primarily contrasted the overall brain activity evoked by perceived and unperceived stimuli
This comparison may be contaminated by non-specific attention, alerting, performance, and reporting confounds

Summary

Introduction

The scientific investigation of consciousness divides into two major branches (Koch, 2004; Dehaene et al, 2014). The first branch, which studies the ‘state of consciousness’, focuses on general vigilance or a person’s ability to perceive, interact, and communicate with the environment, by examining the regulation of sleep and waking, and their pathological disruption by coma, epilepsy, and sleep disorders (Laureys et al, 2004). The second branch of inquiry, which studies ‘access to consciousness’, focuses on the processes that make a specific content subjectively experienced—what differences in brain activity distinguish conscious vs unattended or subliminal stimuli (Dehaene et al, 2006). In order to examine the neuronal processes that underlie conscious states, the neuronal activity associated with one state of consciousness (e.g., sleep) is compared to another (e.g., awake). In order to extract the neural correlates of conscious perception, threshold-level stimuli are presented to the subject such that they are sometimes consciously

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