Hippocampus Neurons Detect Sounds and Language Under Anesthesia

Neurosurgeons inserted high-density Neuropixels probes into the hippocampi of seven patients undergoing epilepsy surgery. The patients were under general anesthesia when researchers played sequences of uniform tones interspersed with occasional oddball tones of different frequency.

More than 70 percent of the monitored neurons responded to the audio and improved at distinguishing the rare tones from the standard tones over a 10-minute session. Separate patients heard 10 to 20 minutes of educational videos and storytelling podcasts while the same probes recorded activity.

Individual neurons responded to the length, type, and meaning of spoken words. Their firing patterns could also predict the meaning of upcoming words in a sentence. The same patterns of activity have been observed in awake brains, yet the anesthetized patients showed no signs of regaining consciousness during the recordings.

The findings indicate that some language and prediction computations can occur without producing awareness or memory. Researchers noted that these results challenge theories that require consciousness for speech processing and word prediction. The work leaves open the question of what functions consciousness serves if complex neural computations can proceed independently of it.