A new study has found that the human brain remains surprisingly active during anaesthesia, continuing to process sounds and even recognise patterns in language despite the person being unconscious.
Researchers behind the study, published in the journal Nature, say the findings challenge long-standing assumptions that the brain largely shuts down under general anaesthesia. Instead, parts of the brain appear capable of analysing speech and predicting words even when awareness is absent.
“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 and researcher at Baylor College of Medicine.
“Even when patients are fully anaesthetised, their brains continue to analyse the world around them,” he added.
The research focused on seven patients undergoing epilepsy surgery aimed at removing sections of the temporal lobe to reduce severe seizures. During the procedures, scientists used advanced Neuropixels probes, ultra-thin silicon devices capable of recording activity from large numbers of neurons at the same time.
The team first examined how the brain reacted to sound. Patients were played a series of repeated tones that were occasionally interrupted by a different sound. Researchers discovered that about 71 percent of monitored neurons responded to the tones, indicating that the brain was still registering audio information while unconscious.
Around a quarter of those neurons reacted specifically to the unusual tones, showing that the brain could distinguish changes in sound patterns. Scientists also observed that the brain’s ability to detect these unexpected sounds appeared to strengthen over time.
In a second experiment, four patients listened to podcast recordings while under anaesthesia. Researchers found that their brains processed speech in real time, reacting not only to individual words but also to broader features of language.
One of the study’s most striking findings was evidence that the unconscious brain could anticipate upcoming words based on the context of a sentence.
“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 and co-author of the research.
Scientists say the findings could reshape understanding of consciousness and brain function during medical procedures. The study may also help researchers better understand how the brain behaves during sleep, coma or other altered states of awareness.
The authors stressed that more work is needed before drawing broader conclusions about unconscious brain activity. Future research will aim to determine whether similar neural responses occur in other forms of unconsciousness and how deeply the brain can process external information while awareness is suspended.
