A new study by scientists at the David Geffen School of Medicine at UCLA has provided important clues for one of the great mysteries of anaesthesia: the processes used by structurally normal brains to navigate back to consciousness after anaesthesia.
Previous research has shown that the anaesthetised brain is not ‘silent’ under surgical levels of anaesthesia but rather experiences certain patterns of activity, and spontaneously changes its activity patterns over time, said Andrew Hudson, assistant professor in anaesthesiology. The research team recorded the electrical activity from several areas of the brain associated with arousal and consciousness in a rodent model that had been given the inhaled anaesthetic isoflurane.
They then decreased the amount of anaesthesia, monitoring how the electrical activity in the brain changed and looking for common activity patterns across all the study subjects. They found that brain activity occurred in discrete clumps, or clusters, and that the brain did not jump between all of the clusters uniformly.
A small number of activity patterns occurred consistently in the anaesthetised rodents, dependent upon how much anaesthesia the subject was receiving, and the brain would jump spontaneously from one activity pattern to another. A few activity patterns served as ‘hubs’ on the way back to consciousness, connecting activity patterns consistent with deeper anaesthesia to those observed under lighter anaesthesia.
“Recovery from anaesthesia is not simply the result of the anaesthetic ‘wearing off’, but also of the brain finding its way back through a maze of possible activity states to those that allow conscious experience,” said Hudson. “Put simply, the brain reboots itself.”
Teams at UCLA will go on to test other anaesthetic agents to determine whether they produce similar characteristic brain activity patterns with ‘hub’ states.
Hudson, A.E., Calderon, D.P., Pfaff, D.W., et al. (2014) Recovery of consciousness is mediated by a network of discrete metastable activity states. Proc. Natl. Acad. Sci. (doi: 10.1073/pnas.1408296111)