How movement affects hearing

Ever wondered why we stop moving when we carefully want to listen to someone? This, scientists have found, is not just to prevent unwanted sounds generated by our own movements.

This interplay between movement and hearing also has a counterpart hidden deep in the brain.

Researchers have revealed exactly how the brain's motor cortex, which controls movement, can tweak the volume control in the auditory cortex.

Movement stimulates inhibitory neurons that, in turn, suppress the response of the auditory cortex to tones, the findings showed.

The new lab methods allowed the group to "get beyond a century's worth of very powerful but largely correlative observations, and develop a new, and really a harder, causality-driven view of how the brain works," said the study's senior author Richard Mooney, a professor at Duke University School of Medicine in the US.

The team recorded electrical activity of individual neurons in the brain's auditory cortex in mice.

Whenever the mice moved - walking, grooming, or making high-pitched squeaks - neurons in their auditory cortex were dampened in response to tones played to the animals, compared to when they were at rest.

To find out whether movement was directly influencing the auditory cortex, researchers conducted a series of experiments in awake animals using optogenetics, a powerful method that uses light to control the activity of select populations of neurons that have been genetically sensitised to light.

The findings contribute to the basic knowledge of how communication between the brain's motor and auditory cortexes might affect hearing during speech or musical performance.

Disruptions to the same circuitry may give rise to auditory hallucinations in people with schizophrenia.

The study appeared in the journal Nature.