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

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 [18F]- 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* {approx} 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 (Fishers exact test, two-tailed p {approx} 2.00 x 10-4); metabolic support and perturbational complexity were strongly correlated across conditions (Spearmans {rho} = 0.95). The sole off-diagonal condition -- NREM sleep, with preserved metabolism ([~]56% of normal) but low complexity (PCI {approx} 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.