Are We Actually Hearing Everything?

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A common recurring joke in our society revolves around the concept of selective hearing. Your spouse might say, “He conveniently doesn’t seem to hear anything at my frequency.” Or you may remember your parents saying, “Why do I have to call your name five times before you hear me?”

Scientific Tuning Out

It seems we all have the ability to just tune the ones we love out whenever we’re interested in something else. Now, it seems this joke has become a reality that can be backed by science. Researchers part of a joint study conducted by Carnegie Mellon University and Birkbeck, University of London have developed a new way to passively map the auditory processing centers of the brain. They’re using this mapping to examine the specific ways the brain tunes into a particular frequency while ignoring others.

In the study conducted by these researchers and published in the Journal of Neuroscience, scientists wanted to find out just how the brain is able to tune into certain frequencies while completely tuning out others, just as we are able to listen to one person talk in the middle of a crowded subway platform, or hear our children talk at the other end of a busy dinner table. So, they implemented a non-invasive method to observe and map the specific areas of the brain of study participants that process certain frequencies of sound.

The Study

Researchers asked a number of participants to listen to a series of short tone melodies and to respond when they heard those melodies. They were told to actively ignore any other melody played. Each time they heard the target tone, they indicated such, while blocking out other melodies.

While the participants did this, researchers observed their brains under MRI scanners, specifically the areas of the tonotopic auditory frequency map located in the auditory processing centers of the temporal lobes. (Tonotopic refers to the way different frequencies of sounds are visually arranged and processed in the brain. Tones that are very close in frequency are arranged closely in the same area of the brain.)

While participants listened, different areas on these tonotopic maps were activated, physiologically reflecting the fact that the participants were only tuning in to certain frequencies. These activations were consistent in appearance across all areas of the cortex that dealt with auditory processing.

Discovery

Researches then used a different mapping method called multiparameter mapping to find consistencies with other observations of the brain’s topography and structure. Scientists noticed that areas with thicker myelin insulation around brain synapses were more strongly reacting to certain frequencies. This discovery revealed a new way to map the auditory frequency topography of the brain, which may have significant implications for future research particularly in the cause and treatment of topography deficits.

Future Implications

Deficits in a brain’s topography may be a result of damage caused by concussion, stroke, autism, or aging. They may even be associated with psychological circumstances such as social isolation, depression, cognitive dysfunction and lower workforce participation. As we learn more and more about the topography of the brain we may discover ways to prevent or reverse some damage made to specific areas of the brain due to the above conditions.

 

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