In a scientific first, researchers at University of Iowa Health Care recorded responses from single neurons in the human insula—a brain region linked to emotional processing and perception of bodily sensations—while the participants listened passively to simple sounds. These unique recordings showed that insula neurons respond to sound during passive listening, and the responses are just as fast as those from the auditory cortex, although they do not last as long. The finding suggests a new role for the insula in processing external auditory input, even without active attention.

“The fact that this brain region, which is involved in complex cognition, also responds to simple sounds, even during passive listening, changes how we think about parallel processing of sounds in the brain," says Joel Berger, PhD, UI research assistant professor of neurosurgery and lead author of the study, which was published in the Journal of Neuroscience.

The team recorded and analyzed data from single neurons in humans, from a brain region called the insula, as well as from auditory cortex. They recorded over 340 single neurons in 12 participants undergoing intracranial monitoring, allowing rare insight into deep-brain activity during passive listening. This is the first time anyone has reported single-neuron responses from the human insula to sounds.

The UI researchers found that nearly one‑third of neurons in the posterior insula—and a smaller subset in the anterior insula—responded to tones and clicks. These responses occurred with relatively short onset times and exhibited preferred tuning to specific sound frequencies.

Showing that insula neurons respond to simple sounds during passive listening offers additional insight into how sound may be processed beyond the traditional auditory cortex.

Overall, the study suggests a fundamental reframing of the role of the insula in processing sounds and how these sounds are integrated with our bodily sensations. The results may also have relevance to hearing disorders and brain plasticity following hearing loss.

In addition to Berger, the team included Hiroto Kawasaki, Sukhbinder Kumar, Matthew Howard III, and Kirill Nourski, from the UI Department of Neurosurgery, and Matthew Banks from the University of Wisconsin.

The work was supported in part by funding from the National Institutes of Health.