Brain Continues to Process Language and Predict Words During Anaesthesia, Study Shows

Some parts of the brain remain active under anaesthesia and can identify and process language, according to a study published in the journal Nature. The results showed that neural circuits continue to encode and respond to stimuli even without consciousness.

“Our findings show that the brain is far more active and capable during unconsciousness than previously thought,” said Sameer Sheth, co-author of the study at Baylor College of Medicine.

The researchers studied seven patients undergoing epilepsy surgery to remove part of their temporal lobe to control seizures. Using Neuropixels probes – tiny silicon needles – the team collected data on how the brain processed sound and language without conscious awareness. In a first test, patients listened to a sequence of identical tones occasionally interrupted by a different one.

Around 71% of the neurons responded to the sound, and 25% of them reacted to the different tones. The brain’s ability to detect these unusual sounds improved over time. Researchers played podcasts to four patients and found that the brain processed speech in real time, responding to individual words and different elements of speech.

The brain, even in an unconscious state, was able to anticipate upcoming words based on prior context. “This kind of predictive coding is something we associate with being awake and attentive, yet it’s happening here in an unconscious state,” said Benjamin Hayden, professor at Baylor College of Medicine.

The study’s authors noted that more research is needed to better understand the brain’s activity under anaesthesia and whether the level of neural activity observed can also be found during sleep or other unconscious states.