A neurobiologically realistic computational model of whole-brain haemodynamic signals, perturbed to simulate loss of consciousness, reveals two distinct neurobiological paths to unconscious brain activity. Incorporating PET data on GABA receptor distribution shows that spatially-specific local inhibition reproduces fMRI activity observed during propofol anaesthesia. Incorporating diffusion MRI data from patients with disorders of consciousness shows that randomized neuroanatomical connectivity can also produce the dynamics characteristic of loss of consciousness. The results generalize across anaesthesia and injury datasets, suggesting that increased inhibition and connectome perturbation are distinct routes to the same functional brain dynamics.
Consciousness relies on spatio-temporal interactions between brain integration and functional diversity. Combining graph theory and dynamic functional connectivity, resting-state fMRI data from awake volunteers, propofol-anaesthetised volunteers, and patients with disorders of consciousness showed that cortical networks are especially affected during loss of consciousness in temporal states of high integration, exhibiting reduced functional diversity and compromised informational capacity, while thalamo-cortical functional disconnections emerge during states of higher segregation. Posterior regions of the brain's default mode network show reductions in both functional diversity and integration during unconsciousness. These overlapping reductions in diversity and integration may represent a generalisable biomarker of loss of consciousness.
Advancing scientific research on consciousness is important for addressing clinical and ethical issues in neurology and mental health. To support this field, funding priorities must be set carefully, and challenges such as job creation and media misrepresentation need to be addressed.