Brain network connectivity behind speech disorder

Research on the hidden patterns of brain activity needed to produce speech is giving scientists fresh insights into what goes wrong in various speech disorders.

Speaking is one of the most complex human cognition processes the brain controls. Speech depends on the precise coordination of more than 100 muscles (spread across the mouth, lungs and vocal cords) when the brain sends the correspondent information to each of these muscles to voice distinct phonemes. If the brain sends continuous information to the muscles and they move in the exact pattern needed, words will just flow from your mouth.

The study of how brain cells are functionally connected in neuroscience is known as connectomics. Currently, it is a broader trend in neuroscience because if scientists understand the brain networks and how they work in a coordinated task-specific like speech, they can know what is causing such abnormalities and develop new diagnostics and treatments.

However, brain researchers are not sure yet how one region of the brain influences another or how the whole brain network works. As a result, doctors don’t have the tools they would like to have to help patients as much as they could.

In the Wall Street Journal, the writer of the article about this topic had an interview with a neurosurgeon at the University of California that is mapping brain activity as people pronounce simple syllables. The main goal of this researcher is to understand the brain patterns of speech-related activity so precisely that doctors can focus on that particular part of the brain in case a brain implant needs to be implanted.

Spasmodic dysphonia, which is incurable, is a neurological movement disorder that causes muscles to contract and spasm involuntarily. This kind of neurological disorder is now considered to be part of conditions called dystonias, and can be generalized, affecting the entire body, or focal, affecting only a specific area of the body or group of muscles. Following Parkinson’s disease and essential tremor, dystonia is the third most common movement disorder.

In certain dystonias, including SD, muscles spasm only when they are used for particular actions and not when they are at rest. When a person with SD attempts to speak, involuntary spasms in the tiny muscles of the larynx cause the voice to break up, or sound strained, tight, strangled, breathy, or whispery. The spasms often interrupt the sound, squeezing the voice to nothing in the middle of a sentence, or dropping it to a whisper. However, during other activities, such as breathing and swallowing, the larynx functions normally.

The disorder affects many different interacting brain areas and patients with SD exhibit different structure, function and connectivity between brain regions compared to people who don’t have the condition.

For more information about research done in this line, please read the article from the WSJ.

References

[1] National Spasmodic Dysphonia Association website.

[2] “The brain wiring behind a frustrating speech disorder” written by Daniela Hernandez in The Wall Street Journal (article).

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