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

Neural correlates of consciousness are often evaluated along single dimensions, such as large-scale integration or metabolic activity, yet it remains unclear whether either is sufficient, or whether conscious states require the joint satisfaction of multiple biological constraints. Here, we evaluate the prediction that conscious states occupy a regime defined by the co-occurrence of sufficient metabolic support and preserved perturbational complexity.

We performed a targeted 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 and perturbational complexity index (PCI) values were mapped across disorders of consciousness, sleep, and anaesthesia into a shared two-dimensional state space.

Across independent cohorts, a lower bound near ~42–46% of normal cortical metabolism and a complexity threshold near PCI* ≈ 0.31 consistently separate unconscious from conscious conditions. Of 16 conditions with complete data, all 9 conscious states occupied the joint regime (above both thresholds), while all 7 unconscious states fell below at least one threshold (Fisher’s exact test, p = 8.74 × 10 ⁻⁵ ). The sole off-diagonal placement — NREM sleep, with preserved metabolism but reduced complexity — was unconscious, supporting the prediction that metabolic support alone is insufficient without preserved integrative dynamics.

These findings support a joint metabolic–integrative constraint on consciousness and motivate a testable prediction: reportable experience should not occur outside this regime. Direct evaluation will require prospective within-subject multimodal studies combining FDG-PET and TMS–EEG.