What is the difference between the “hearing brain” and the “deaf brain”?

In the video, we present research conducted by the Institute of Psychology at the Jagiellonian University. The research group was led by Dr. Marcin Szwed.

Dr. hab. Marcin Szwed from the Institute of Psychology at Jagiellonian University, together with his research team, analyzed the function of the auditory cortex in deaf individuals. There were few scientific studies on the functioning of this brain area in people who are deaf. Scientists knew that a certain part of the auditory cortex in deaf individuals assists the visual cortex in seeing things from the corner of the eye, which allows deaf individuals to have a broader field of view, enabling them to perceive stimuli they cannot hear, such as approaching cars.

But what about the rest of the auditory cortex?! It is not responsible for hearing! For scientists, this was even more interesting because they confirmed the presence of a well-developed visual rhythm, known as the “visual beat,” in deaf individuals. This means they have the ability to recognize rhythm in visual signals from the environment, such as flashing lights. However, until then, it was not known how this is possible and what processes occur in the brain of a deaf person. How is it possible then that the deaf have a sense of rhythm?

Sense of rhythm in deaf individuals

The team led by Dr. Szwed was inspired by an experiment conducted by other scientists who studied synesthetes, individuals in whom stimuli from one sense evoke experiences typical of another sense. Dr. Szwed conducted a study involving deaf individuals to analyze and compare how the “hearing brain” and the “deaf brain” would function when it comes to tasks related to perceiving rhythm. The study included 15 hearing individuals and 15 individuals born deaf with profound hearing loss. Magnetic resonance imaging was used to observe the brain activity of the participants.

During the study, individuals without hearing impairments heard rhythmic sounds, while deaf participants only watched flashing circles. The circles were presented precisely in the same rhythm as the sounds in the study with the hearing individuals. Both groups had to judge whether two consecutive series of rhythms were the same or different. It turned out that a part of the auditory cortex, which is responsible for sensing and processing rhythm in sounds, completely switched to vision in deaf individuals!

When a hearing person hears music, the auditory cortex is automatically activated, which is mainly responsible for recognizing rhythm. As explained by Dr. Szwed:

“the exact same part – down to the millimeter – is activated in deaf individuals when they see flashing lights, or any other visual rhythm.”

Incredible plasticity of the brain

So, the study shows that the auditory cortex, responsible for rhythm, “switches” from one sense to another: from hearing to vision! In summary, the auditory cortex in deaf and hearing individuals serves the same function, but thanks to the brain’s plasticity, it accomplishes this task in a different way, specifically by drawing information from a different sense!

Previously, scientists described numerous studies involving blind individuals, which reported a similar phenomenon of changes in the functioning of the visual cortex. The conclusions from such research allow us to infer a general rule of reorganization in the brain’s cortex. The task of a specific area remains unchanged, but the sense used to execute that task changes!

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