• Distinct neural activity patterns carried information about word categories, including nouns, verbs and adjectives.
• The hippocampus responded to meaningful features of language rather than merely registering that sounds were occurring.
• Neural activity contained information that could be used to predict upcoming words in a sentence.

That last result is the most consequential. "The brain appears to anticipate what comes next in a story, even without conscious awareness," said Sheth, who also directs The Gordon and Mary Cain Pediatric Neurology Research Foundation Laboratories within the Duncan Neurological Research Institute at Texas Children's Hospital.

The ability relates to a process called predictive coding: rather than passively receiving information, the brain continually uses patterns and prior experience to anticipate what follows. Scientists normally study this kind of prediction in awake, attentive listeners. Finding it under anesthesia suggests at least some of the underlying neural processes can operate independently of consciousness.

"This kind of predictive coding is something we associate with being awake and attentive, yet it's happening here in an unconscious state," said Dr. Benjamin Hayden, professor of neurosurgery at Baylor.

What does this mean for consciousness?

The findings do not mean the patients consciously understood the stories. They mean the brain can perform surprisingly complex language processing without a person knowing it is happening.

That distinction may help researchers understand how consciousness emerges. One possibility: awareness depends not on whether individual brain regions stay active, but on how information is coordinated and shared across larger networks. Under this view, the hippocampus might keep analyzing information even when the broader communication required for conscious experience is disrupted.

The study also highlights a parallel with artificial intelligence. Large language models, the technology behind modern chatbots, generate text by using patterns learned from enormous amounts of language data to predict what comes next. The hippocampus showed a related predictive ability, though biological brains and AI models operate in fundamentally different ways.

Could this help people who cannot speak?

The practical implications point toward brain-computer interfaces (devices that translate brain signals into commands for external technology), and specifically toward speech prosthetics, which aim to restore communication after injury or neurological disease impairs speech.

"Can we use these signals to deploy and run a speech prosthetic for some of the parts of the brain that are damaged by stroke or injury? These are questions that we can now consider in relation to this part of the brain," said Dr. Vigi Katlowitz, first author of the study and a neurosurgery resident at Baylor.

What are the study's limits?

The researchers urge caution. The experiments involved a single type of general anesthesia, so the results may not extend to other anesthetic methods or to states such as sleep or coma, which differ significantly from medically induced unconsciousness. The study also examined only the hippocampus; further work must determine whether other brain regions show comparable abilities and how they interact when consciousness is absent.

The first author is listed in the journal as Kalman A. Katlowitz; the full 23-author team published its results as "Plasticity and language in the anaesthetized human hippocampus" in Nature, volume 654.

Even with those caveats, the evidence is compelling: unconsciousness does not mean the brain has stopped. "This work pushes us to rethink what it means to be conscious," Sheth said. "The brain is doing much more behind the scenes than we fully understand."