Inside the unconscious brain

A new study from MIT and Massachusetts General Hospital (MGH) reveals, for the first time, what happens inside the brain as patients lose consciousness during anaesthesia .

By monitoring brain activity as patients were given a common anaesthetic, the researchers were able to identify a distinctive brain activity pattern that marked the loss of consciousness. This pattern, characterised by very slow oscillation, corresponds to a breakdown of communication between different brain regions, each of which experiences short bursts of activity interrupted by longer silences.

''Within a small area, things can look pretty normal, but because of this periodic silencing, everything gets interrupted every few hundred milliseconds, and that prevents any communication,'' says Laura Lewis, a graduate student in MIT's Department of Brain and Cognitive Sciences (BCS) and one of the lead authors of a paper describing the findings in the Proceedings of the National Academy of Sciences this week.

This pattern may help anaesthesiologists to better monitor patients as they receive anaesthesia , preventing rare cases where patients awaken during surgery or stop breathing after excessive doses of anaesthesia  drugs.

''We now finally have an objective physiological signal for measuring when someone's unconscious under anaesthesia ,'' says Patrick Purdon, an instructor of anaesthesia  at MGH and Harvard Medical School and senior author on the paper. ''Now clinicians will know what to look for in the EEG when they are putting someone under anaesthesia .''

Other MIT authors of the PNAS paper are co-lead author Veronica Weiner, a graduate student in BCS, and Emery Brown, professor of brain and cognitive sciences and health sciences and technology at MIT and an anesthesiologist at MGH.