Brain and the connection with hearing loss.

Several parts of the body have to work together for us to understand sound. We commonly think of ear problems as leading to hearing loss, but researchers are still studying the extent to which problems at the brain level could be the culprit. A researcher at Tulane University is studying the brain’s role in hearing in mice, and he is using a new method that could help shed light on human hearing.

New Research Into the Brain and Hearing Loss

The National Institute on Deafness and Other Hearing Disorders has given a $1.8 million grant to a researcher at Tulane University to study a specific section of the synapses in mice that receive auditory signals. This research is important because prior studies have focused only on how the brain processes sound after it receives signals. The synapses that receive sound have been considered too small for researchers to be able to record what is going on at the site.

Dr. Huang, the Tulane researcher, is going to study a specific synapse called the calyx of Held, which is larger than other synapses that send out the neurotransmitters that help the brain interpret sound. He is going to look at how signals are stored and released at this site, and how signals are recycled to make room for new ones. If he finds a difference at this critical nerve transmission center in mice, it may help explain what leads to hearing loss or poor hearing quality in humans.

How Human Hearing Works

The brain is an important part of the auditory system. The different parts of your ear pick up sound signals and send them to the brain to interpret. The brain receives those nerve signals and then sends them back as “translated” sound.

  • The Outer Ear – The outer ear provides a pathway for sounds and protects the inner structures. The ear canal starts in the outer ear. This is where your body produces earwax to keep dust, bugs and other debris out.
  • The Middle Ear – The middle ear has sensitive bones called the hammer and stirrup that “feel” sound vibrations. The middle ear also controls equalizing pressure between your ear and your environment.
  • The Inner Ear – The inner ear is where the intricate processes of hearing start to take place. The all-important cochlea is in the inner ear. The cochlea is shaped like a snail, and it contains three compartments that are filled with fluid. The cochlea is surrounded by tiny hairs that serve as nerve cells, also called cilia. When the fluid in the inner ear is stimulated by sound, these tiny hairs release chemical responses that head to the brain by way of auditory nerves.
  • The Brain – The brain accepts the signals it receives from the auditory nerves, and it goes through a complex process to understand and interpret them in a way that we can understand. It probably never occurred to you to ask why you remember the voices of your loved ones, or even someone you met only once. That’s your brain storing sounds and recognizing them when they return. The brain accomplishes all of this through a series of nerves. The nerves talk to each other via synapses that sit between them. Some synapses release sound signals through neurotransmitters, while others synapses detect these signals.

Why Do We Study Hearing Loss in Mice?

It may seem strange to study the auditory systems of mice to try to understand problems in human hearing. Interestingly, the physiology of mice and the way they hear is remarkably similar to humans. It is also very easy to determine through a simple test if mice have hearing loss, making it easy to compare them to mice with healthy hearing.

Hearing is a very complex process, and we can’t discount the role of the brain. Changes that occur in the auditory system at any level can not only affect whether or not sounds are loud enough, but whether there is distortion that leads to misunderstanding speech and other sounds. Identifying brain-level problems can lead us down several paths to improve the quality of life for those with hearing loss.

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