This study explores how the brain processes predictions and what happens to these processes during unconsciousness induced by the anesthetic propofol.

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Our brains are constantly making predictions about our surroundings, enabling us to focus on and respond to unexpected events. A recent study explores how this predictive process functions during consciousness and how it changes under general anesthesia. The findings support the idea that conscious thought relies on synchronized communication between basic sensory areas and higher-order cognitive regions of the brain, facilitated by brain rhythms in specific frequency bands.

Previously, members of the research team at The Picower Institute for Learning and Memory at MIT and at Vanderbilt University had described how brain rhythms enable the brain to remain prepared to attend to surprises. Cognition-oriented brain regions (generally at the front of the brain), use relatively low-frequency alpha and beta rhythms to suppress processing by sensory regions (generally toward the back of the brain) of stimuli that have become familiar and mundane in the environment (e.g. your co-worker’s music). When sensory regions detect a surprise (e.g. the office fire alarm), they use faster frequency gamma rhythms to tell the higher regions about it and the higher regions process that at gamma frequencies to decide what to do (e.g. exit the building).

Anesthesia’s Impact on Brain Communication

The new results published Oct. 7 in the Proceedings of the National Academy of Sciences, show that when animals were under propofol-induced general anesthesia, a sensory region retained the capacity to detect simple surprises but communication with a higher cognitive region toward the front of the brain was lost, making that region unable to engage in its “top-down” regulation of the activity of the sensory region and keeping it oblivious to simple and more complex surprises alike.

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