What happens in the anaesthetised brain when people become unresponsive?

What is it about?

We looked at how brain activity changes when individuals become unresponsive under anesthesia. We recorded the brain activity of healthy volunteers when they experienced a really slow loss of consciousness during FMRI and EEG. We found that activity in the dorsal anterior part of brain region called the insula was significantly reduced to several different types of external sensory stimuli (such as words, beeps and pain) when people became unresponsive. This region is called the dorsal anaterior insula cortex (dAIC). We also showed that how well the dAIC is connected to frontal and parietal regions of brain changes as people become unresponsive.

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Why is it important?

Changes in the brain's stimulus-evoked responses under anaesthesia have not been investigated in such detail before. Importantly, we found activity in most brain regions classically associated with the perception of these stimuli were unchanged when people become unresponsive under anesthesia. We suggested that the observed changes in the dAIC brain regions may indicate a loss of 'selfhood' - meaning the stimuli are 'perceived' by the brain but maybe not associated with one's self. We showed that changes in the connectivity of the dAIC brain region acts as a seed for breakdown in other known 'consciousness' networks, with a bias towards those associated with decision making at this anaesthetic depth.