Does Your Brain Let You Hear Your Own Footsteps?

Our brains may be equipped with a noise-cancelling feature: to help us ignore the sound of our own footsteps or the crunch of biting objects.

In a new study with mice, the mice’s brains cancelled out the sound of their own footsteps. The ability helped the mice better hear other sounds in their environment, researchers report today (Sept. 12) in the journal Nature.

For a mouse walking around a field, “it’s better to hear the cat than to hear your own footsteps,” said senior study author Richard Mooney, a professor of neurobiology at Duke University.

Mooney and his team used mice to study their “acoustic virtual reality system.” They implanted tiny electrodes into their auditory cortex – the area of the brain that processes sound – and had the mice run on a treadmill under a microscope so they could also take real-time images of the brain.

To understand how the brain processes sounds associated with the animals’ own movements, the researchers created artificial footsteps – sounds the mice wouldn’t encounter in the wild. With each step the mice took, the researchers popped a quick note or “sound pipe.” Mooney told Live Science to imagine that the mice are running on a small piano. But “every key would play the exact same note,”

Mooney and his team found that after thousands of footsteps over a two- to three-day period, activity in the auditory cortex decreased.

But when the researchers changed the sound of the lute, the auditory cortex became more active. That could also explain why you can hear your footsteps if, say, you’re ever wearing loud boots, which you normally wouldn’t, Mooney says.

“Experience can shape how the brain suppresses predictable sensations generated by movement,” he says.

Their imaging and measurements showed a strong coupling between the motor cortex – an area of the brain associated with movement – and the auditory cortex. During training, the motor cortex begins to form synapses, or connections to the auditory cortex. These connections eventually act as a noise filter.

So-called inhibitory neurons, or brain cells in the motor cortex, begin to send signals to counteract the firing of the neurons in the auditory cortex that make us aware of sound. The process is so fast that it’s “predictive,” says Mooney, meaning the cancellation signal occurs at the same time as the brain commands movement.

The researchers also found that mice trained to ignore the sound of their own footsteps were better able to detect abnormal or new sounds while running than untrained mice trained to ignore the sound of their own footsteps.

Mooney believes that these results translate very clearly to humans. Although the human cortex is much more advanced, “the basic brain structure between the motor cortex and auditory cortex is present in all the mammals studied,” he says.

“Mice don’t play the piano, at least none that I’m aware of,” Mooney said. For them, the ability to suppress sounds associated with movement is more of a survival benefit, such as being better aware of potential predators.

This may be true for humans as well, but this auditory adaptation may also allow humans to engage in complex tasks, such as learning to speak, play an instrument or sing, Mooney says.

This system can train your brain to expect the notes you play or sing.” Once you have a good prediction of what should happen…. . you’re also very sensitive to whether it turns out differently.”

(It’s well known that a similar motor system exists in the human brain. For example, figure skaters. Their brains learn to anticipate movements and begin to cancel reflexes that would prevent their heads from spinning. However, if a figure skater lands incorrectly, the brain thinks it’s unexpected and doesn’t fire its inhibitory neurons – and the fall-capture reflex kicks in).

In addition, Mooney claims that understanding this system is beneficial to the study of psychosis. For example, a common symptom of schizophrenia is sound-like hallucinations, which he says are thought to be caused by a “broken” prediction circuit in the brain. In other words, auditory brain cells aren’t so inhibited that they fire too much, even if there’s no external sound to trigger them.