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Neurons “Meta-Adapted” to Our Rowdy World

A study published in Nature Communications has revealed how auditory neurons in the brain cope in both quiet and loud environments, with the results opening a new avenue to investigate why some people find it difficult to follow a conversation in a noisy environment.

“We discovered that neurons quickly adapt to the current sound environment being experienced – quiet or loud – and adjust to maximise the transmission of information about the current environment,” said Prof David McAlpine of Macquarie University.

“However, what is really interesting is how these neurons adjust: their adaptation process itself adapts as sound environments become increasingly familiar. For example, after experiencing a sound environment five or six times, neurons are able to adapt twice as fast as when they first experienced it, in a process we’ve called ‘meta-adaption’.”

The study measured the neural response of guinea pigs, which have similar hearing range to our own, by exposing them to relatively quiet or loud unfolding soundscapes. It found that parts of the brain held onto these sound memories much longer than expected due to a feedback loop between the midbrain and the auditory cortex. The discovery of this loop indicated a previously unknown connection between these two brain regions.

“One of the unusual things we found was that the midbrain – a part of the brain that is thought to retain information for only a few hundreds of milliseconds – was actually retaining the information it learned about how an environment sounded over many minutes, which was what allowed the auditory neurons to meta-adapt. When we blocked this loop the neurons could no longer adapt, indicating a relatively unexplored loop function between these brain regions,” McAlpine concluded.