Towards a bridge between intracerebral and surface EEG signatures of conscious report

A recent study using intracerebral electroencephalography (EEG) recordings in human patients has documented the electrophysiological correlates of conscious reporting of near-threshold visual targets that followed supra-threshold peripheral spatial cues. Here, we aimed to bridge these intracerebral EEG events with corresponding surface recording, differentiating between conscious and nonconscious processing. We analysed the surface EEG of 10 patients from the intracerebral study. Due to a limited number of surface derivations, we pooled trials across participants to create a virtual participant for both surface and intracerebral analyses. Event-related potential (ERP) analysis revealed a significant positive deflection for Seen compared to Unseen targets in the 350-500 ms post-target window at frontal sites, consistent with a P3b component associated with conscious report. Time-frequency analysis revealed spectral dynamics associated with conscious report, including pretarget beta/gamma power modulations at frontal electrodes and post-target increased oscillatory activity at occipital sites. Trajectory k-means clustering of intracerebral data enabled us to identify two key patterns of post-target activity closely corresponding to the clusters from the original study: a Visual cluster exhibiting early (120-340 ms), transient responses, and an Accumulation cluster demonstrating gradual activity buildup (230-490 ms). Ridge regression analysis revealed that, compared to the Visual cluster, the Accumulation cluster contributed more to the prediction of report-related ERPs at the scalp level. These findings offer insights into bridging the gap between intracerebral recordings and surface EEG correlates of conscious report. They also highlight the greater contribution of late integrative mechanisms, compared to early sensory processes, in the conscious experience of behaviourally relevant targets.