What Does the Brain Organise When It Becomes Conscious? Spatial Efficiency of Neural Oscillations as an EEG Marker of Phenomenal State

A new EEG metric called spatial efficiency (η) tracks the organization of conscious experience by measuring how brain activity is spatially structured across frequency bands, rather than just its complexity. Unlike standard complexity measures that are inflated by amplitude increases during sleep or sedation, η remains accurate. Across four datasets, η distinguished awake from sedated states with near-perfect accuracy (AUC 0.988–1.000), outperforming Lempel-Ziv Complexity (AUC 0.612–0.755). During sleep, η correctly ranked states from wake to REM to deep sleep, and detected the presence of phenomenal content during dreaming. It also detected transient drops during cognitive restructuring in conscious subjects, showing sensitivity to changes within conscious experience that other metrics miss.

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Abstract

Abstract A fundamental question for consciousness science is what changes in the brain when phenomenal experience arises or restructures. Current EEG metrics of consciousness predominantly measure temporal signal complexity, but face a systematic confound: broadband amplitude increases during propofol sedation and slow-wave sleep paradoxically inflate complexity measures, misranking states that are phenomenologically distinct. We introduce η (spatial efficiency), defined as the ratio of organised oscillatory power to total oscillatory power across five frequency bands: η = ||Ψ|| / ||A||, where Ψ is the Effective Power Vector (amplitude weighted by spatial pattern stability) and A is the total amplitude vector. Because η normalises by amplitude, it is immune to the confound that defeats temporal complexity measures. We validate η across four independent EEG datasets. In two propofol sedation datasets (N=21 and N=20), η achieves AUC=0.988–1.000 for awake versus sedated classification, dramatically outperforming Lempel-Ziv Complexity (AUC=0.612–0.755), which increases paradoxically under light sedation. In a polysomnographic sleep dataset (N=7), η follows the gradient Wake > REM > N2 > N3 with r=−1.000 in every subject across NREM stages, and correctly places REM above N3 (d=+1.78, p=0.016) — a dissociation that operationalises the presence of phenomenal content during dreaming. In a reversal learning dataset (N=22), η falls transiently when conscious subjects undergo cognitive restructuring (d=−2.58, p<0.001), demonstrating sensitivity to intra-conscious phenomenal transitions that consciousness-level metrics cannot detect. We interpret these results within multiple theoretical frameworks and argue that spatial efficiency constitutes a new class of EEG consciousness metric — one that tracks not merely whether a subject is conscious, but how organised their phenomenal state is. Keywords: consciousness; EEG; spatial organisation; sleep; propofol sedation; thermodynamics; Lempel-Ziv complexity; integrated information theory; global workspace theory