Abstract
Deep anaesthetisation is an important surgical and explorative tool in the study of consciousness. Much work has been done to connect the deeply anaesthetised condition with decreased functional complexity. However, anaesthesia-induced unconsciousness is also a dynamic condition in which functional activity and complexity may fluctuate, being perturbed by internal or external (e.g. noxious) stimuli. We use fMRI data from a cohort undergoing ultra-slow propofol induction and a dynamic graph modelling framework which characterises changes in functional activity and connectivity as changes in brain state. We examine the group-level dynamics of brain state activity, complexity, integration and modularization in deep anaesthesia and wakefulness and propose novel measures for temporal complexity of brain state dynamics. We find that deep anaesthesia states are less temporally complex and less functionally-related to one another than wakeful states. Anaesthesia dynamics are dominated by a handful of sink states that act as low-complexity attractors to which subjects repeatedly return. Our analysis suggests that dynamic functional organisation in anaesthesia can be characterised by temporally stable, modular communities that change little in time, stratifying regional activity and functionally isolating cortical from both subcortical, and in particular, thalamic brain areas. Using data from a large human structural tractography atlas, we show that functional modularisation in deep anaesthesia more closely resembles normative structural organisation than does functional organisation in wakefulness. We find evidence suggesting that brain state trajectories and in particular, the dominance of low complexity attractor-like sink states in anaesthesia, appear to depend on subject-specific age and anaesthesia susceptibility factors.
Competing Interest Statement
The authors have declared no competing interest.
