A joint metabolic–integrative regime of consciousness: evidence from FDG-PET and TMS–EEG

Abstract

Abstract Conscious experience is associated with both sufficient cerebral metabolic support and preserved large-scale neural integration, yet these two constraints have largely been studied in isolation. Whether consciousness requires their joint satisfaction — and whether either alone is sufficient — remains an open question. Here, we test the prediction that conscious states occupy a joint metabolic–integrative regime defined by the co-occurrence of adequate metabolic support and preserved perturbational complexity. We performed a constraint-driven cross-study synthesis of published benchmarks from [ 18 F]- fluorodeoxyglucose positron emission tomography (FDG-PET) and transcranial magnetic stimulation combined with electroencephalography (TMS–EEG). Metabolic values (expressed as percentage of normal cortical metabolism) and perturbational complexity index (PCI) values were mapped across canonical states spanning disorders of consciousness, sleep, and anaesthesia into a shared two-dimensional state space. A metabolic lower bound of ∼42–46% of normal cortical metabolism and a complexity threshold of PCI* ≈ 0.31 consistently separated unconscious from conscious conditions across independent cohorts. Of 15 conditions with complete data on both axes, all 9 conscious states occupied the joint regime (above both thresholds) and all 6 unconscious states fell below at least one threshold (Fisher’s exact test, two-tailed p ≈ 2.00 × 10 −4 ); metabolic support and perturbational complexity were strongly correlated across conditions (Spearman’s ρ = 0.95). The sole off-diagonal condition — NREM sleep, with preserved metabolism (∼56% of normal) but low complexity (PCI ≈ 0.23) — was unconscious, consistent with the prediction that metabolic support is necessary but not sufficient without preserved integrative dynamics. These findings support a joint metabolic–integrative constraint on conscious experience. The framework yields a clear falsification target: reportable experience should not occur in conditions falling outside this joint regime. Prospective within-subject studies combining FDG-PET and TMS–EEG are needed to evaluate this prediction at the individual level.