A study led by researchers from University of Turku and Turku University Hospital has identified the probable origin of stuttering in the brain. This discovery sheds light on the neurobiological mechanisms underlying this speech rhythm disorder, which affects approximately 1% of adults worldwide.
"Stuttering was once considered a psychological disorder. However, with further research, it is now understood to be a brain disorder related to the regulation of speech production," said Juho Joutsa, senior author of the study published in Brain.
The researchers developed a novel research design that included individuals who developed stuttering after suffering a stroke. Remarkably, despite the strokes occurring in different brain regions, they all localized to the same brain network, distinct from strokes that did not cause stuttering.
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Additionally, magnetic resonance imaging (MRI) scans of 20 individuals with developmental stuttering revealed structural changes in the nodes of this identified brain network. "The greater the changes, the more severe the stuttering," Joutsa explained, suggesting a common neurological basis for stuttering, regardless of its developmental or neurological origin.
The key nodes of the implicated network are the putamen, amygdala, and claustrum—deep brain structures and their interconnections. "These findings explain well-known features of stuttering, such as the motor difficulties in speech production and the significant variability in stuttering severity across emotional states," Joutsa said. The putamen regulates motor function, the amygdala regulates emotions, and the claustrum acts as a hub, relaying information between various brain networks.
This discovery provides a unique insight into the neurobiological basis of stuttering and opens up new possibilities for medical treatment. In the future, stuttering could be effectively treated, for example, with brain stimulation that can be targeted specifically to the now identified brain network, the team reported.