Root causes of stuttering investigated.

An international team of researchers, spearheaded by experts from the University of Turku and Turku University Hospital in Finland, has made a significant breakthrough in identifying the likely origin of stuttering in the brain. Stuttering, characterized by involuntary repetitions, prolongations, or pauses in speech, disrupts normal speech production. While approximately 5-10% of young children stutter, about 1% continue to experience this speech rhythm disorder into adulthood, and severe stuttering can greatly impair an individual's quality of life.

Historically, stuttering has been viewed as a psychological disorder, but researchers, including Professor of Neurology Juho Joutsa from the University of Turku, now recognize it as a brain disorder tied to the regulation of speech production. Stuttering can also occur due to neurological diseases like Parkinson's disease or stroke. Despite extensive studies, the neurobiological mechanisms underlying stuttering remain elusive, and pinpointing its exact location in the brain has been challenging due to partly contradictory findings from brain imaging studies. Distinguishing the root causes from associated phenomena has posed a significant challenge.

The international research team from Finland, New Zealand, the United States, and Canada developed an innovative research design that may address these uncertainties. The study involved individuals who had suffered strokes, some of whom developed stuttering immediately afterward. Surprisingly, although the strokes occurred in different brain regions, they all localized to the same brain network, in contrast to strokes that did not result in stuttering. The researchers also performed magnetic resonance imaging (MRI) scans on the brains of 20 individuals with developmental stuttering. They found that stuttering in these individuals correlated with structural changes in key nodes of the brain network previously linked to stroke-induced stuttering. The greater these changes, the more severe the stuttering, implying that stuttering stems from a common brain network irrespective of its developmental or neurological origin. The research identified several critical nodes within this network, including the putamen, amygdala, and claustrum, all located deep within the brain and connected by various pathways.

“These findings elucidate well-known features of stuttering, such as motor difficulties in speech production and significant variability in stuttering severity across different emotional states,” explains Joutsa. “The putamen plays a crucial role in regulating motor function, the amygdala regulates emotions, and the claustrum acts as a hub, relaying information between several brain networks." This groundbreaking study offers unique insights into the neurobiological basis of stuttering, presenting new avenues for medical treatment. The researchers are optimistic that these findings will pave the way for targeted medical interventions, such as brain stimulation, aimed specifically at the now-identified brain network to effectively treat stuttering in the future.