General anaesthesia as fragmentation of selfhood: insights from electroencephalography and neuroimaging

Summary

Selfhood depends on brain processes that allow a person to experience being a distinct, capable agent. It includes a hierarchy of components: core self (awareness of existence), embodied self (sentience), executive self (agency), and higher-order cognition. Consciousness and selfhood are related but not identical; understanding selfhood helps explain partial consciousness during anesthesia. Brain-imaging and EEG studies show that anesthetic drugs selectively impair self-related networks, especially the anterior insula and salience network, causing depersonalization at moderate doses while preserving disembodied self-awareness. Unlike natural sleep, where loss of agency and sentience tracks with decreasing self-awareness, anesthesia maintains posterior brain connectivity even at high concentrations, possibly marking a core self involved in reduced energy homeostasis.

Study at a glance

Abstract

Selfhood is linked to brain processes that enable the experience of a person as a distinct entity, capable of agency. This framework naturally incorporates a continuum of both non-conscious and conscious self-related information processing, and includes a hierarchy of components, such as awareness of existence (core self), embodied self (sentience), executive self (agency/volition), and various other higher-order cognitive processes. Consciousness relates to, but is not congruent, with selfhood; understanding the processes required for selfhood can explain the partial consciousness seen in anaesthesia. Functional-brain-imaging and electroencephalographic studies in sleep and general anaesthesia have shown differential effects of anaesthetic drugs on various specific self-related functional brain networks. In particular, drug-induced selective impairment of anterior insula function suggests there might be a crucial difference between anaesthesia and natural sleep when it comes to the salience network. With increasing concentrations of anaesthetics, it is not uncommon for patients to become depersonalised (i.e. to lose sentience and agency), but retain many higher-order functions and a disembodied self-awareness, until quite high concentrations are reached. In this respect, general anaesthesia differs significantly from physiological sleep, where it appears that loss of agency and sentience parallels, or lags behind, the decrease in self-awareness. Interestingly, connectivity within the posterior brain regions is maintained even to quite high concentrations of anaesthetics, potentially representing a pathognomonic marker of the core self that possibly is involved in maintaining a reduced energy state of homeostasis.