Do you know when you’ve accidentally closed a car door on the seatbelt just by hearing the sound?
Surprisingly, that feeling that something just ‘didn’t sound right’ – whether it’s the front door not closing properly behind you, or the sound of ball on bat as a cricket ball is unexpectedly (and often inexpertly) lobbed to ‘cow corner’ – uses the same brain circuitry involved in speaking, playing music and in diseases such as schizophrenia.
A collaboration of neuroscientists in the US has investigated how the brain processes audio information and makes decisions about what sounds ‘wrong’ and what sounds ‘right’.
“We listen to the sounds our movements produce to determine whether or not we made a mistake,” says David Schneider, an assistant professor in New York University’s Centre for Neural Science and the senior author of the paper, which appears in the journal Current Biology. “This is most obvious for a musician, or when speaking, but our brains are actually doing this all the time, such as when a golfer listens for the sound of the club making contact with the ball. Our brains are always registering whether a sound matches or deviates from expectations. In our study, we discovered that the brain is able to make precise predictions about when a sound is supposed to happen and what it should sound like.”
Although it is a phenomenon we experience relatively frequently – and probably take for granted when we do – the actual processes that enable our brains to perform this task are not well-understood.
To this end, the researchers studied the activity in the brains of mice performing a task requiring them to push a lever, accompanied by a signature sound.
By recording the neurological activity in the mice when these events occurred, the researchers were able to see how nerve cells were activated within a part of the brain involved in hearing called the auditory cortex.
When the mice pushed the lever and the correct tone was played as expected, the nerve cells, or neurons, were only minimally activated.
However, when the wrong sound was played or the right sound was played at the wrong time, the area lit up with activity.
“The auditory cortex seems to signal not what was heard, but whether what was heard matched or violated its expectations,” observes Nicholas Audette, the lead author on the study and a postdoctoral fellow in the Schneider lab.
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When no sound accompanied pushing the lever, the nerve cells became active at the same moment they would have if there was a sound, suggesting some level of anticipation in the area.
“Because these were some of the same neurons that would have been active if the sound had actually been played, it was as if the brain was recalling a memory of the sound that it thought it was going to hear,” notes Schneider.
This research may also one day be able to help scientists understand more about the phenomenon of hearing voices in patients with diseases like schizophrenia by comparing how the circuitry works in healthy brains compared to those afflicted with disease.