A new study has found that the brain remains active under anaesthesia and continues processing language even when a person is unconscious.

Researchers discovered that certain parts of the brain can still identify and respond to sounds and speech despite the loss of consciousness. The findings, published in the journal Nature, suggest that neural circuits continue to encode and react to external stimuli during anaesthesia.

“Our findings show that the brain is far more active and capable during unconsciousness than previously thought,” said Sameer Sheth, a co-author of the study. He noted that fully anaesthetised patients still appeared to analyse the world around them.

The research involved seven patients undergoing epilepsy surgery, during which scientists used tiny Neuropixels probes to study how the brain processed sound and language without conscious awareness.

In one experiment, patients listened to repeated tones interrupted by different sounds. Researchers found that about 71% of neurons responded to the tones, while 25% reacted specifically to the unusual sounds, indicating that the brain continued detecting changes in audio patterns.

In another test, patients listened to podcasts while unconscious. Scientists observed that the brain processed speech in real time, responding to individual words and speech patterns.

The study also found that the brain could predict upcoming words based on context, a process known as predictive coding. According to Benjamin Hayden, this ability is usually linked to wakefulness and attention, making its presence during unconsciousness particularly significant.

Researchers said further studies are needed to better understand brain activity under anaesthesia and whether similar neural responses occur during sleep or other unconscious states.