Summary: A new international study has identified a common brain network linked to stuttering, regardless of whether stuttering began developmentally or after brain injury. Researchers found that strokes that produced stuttering and cases of developmental stuttering both implicate the same deep-brain regions and their connections.
These results point to potential targeted treatments, such as focused brain stimulation, and clarify which brain areas are most relevant to speech motor control and the emotional fluctuations that affect stuttering.
Key Facts:
- Common network: Stuttering arising from different causes converges on the same brain network.
- Core regions: The putamen, amygdala and claustrum emerge as critical nodes in that network.
- Treatment potential: The discovery opens avenues for targeted therapies, including neuromodulation.
Source: University of Turku
What is stuttering?
Stuttering is a disorder of speech fluency marked by involuntary repetitions, prolongations or pauses that interrupt the normal flow of speech. It affects roughly 5–10% of preschool children, with about 1% of people continuing to stutter into adulthood. For those with severe symptoms, stuttering can have a profound effect on communication, social interaction and quality of life.
“Stuttering was once thought to be primarily psychological, but accumulating evidence shows it is rooted in brain systems that regulate speech production,” says Professor of Neurology Juho Joutsa from the University of Turku.
While many cases begin during development, stuttering can also appear after neurological events such as stroke or in neurodegenerative conditions like Parkinson’s disease. Until now, pinpointing the precise neurobiological origins of stuttering has been difficult because brain imaging studies have produced partly inconsistent findings.
Same brain network for stuttering regardless of cause
Researchers from Finland, New Zealand, the United States and Canada used a novel research design to address this challenge. They examined patients who had suffered strokes, including a subset who developed stuttering immediately following the stroke, and compared these cases with people who have persistent developmental stuttering.
Although the stroke lesions were located in diverse brain regions, lesion network mapping showed that all lesions producing stuttering were functionally connected to a single common network. Lesions that did not cause stuttering did not map to this network.
The team also performed MRI scans on 20 adults with developmental stuttering. In these individuals, structural differences appeared in the very nodes of the lesion-derived network: the greater the anatomical change in those nodes, the more severe the stuttering symptoms.
Taken together, these observations indicate that stuttering—whether developmental or acquired after brain injury—can be localized to a shared brain network centred on deep subcortical structures and their connections.
The principal nodes identified were the putamen, the amygdala and the claustrum, together with the white-matter pathways that connect them. Each of these regions contributes in complementary ways: the putamen is a central motor-regulating nucleus, the amygdala is closely tied to emotional processing, and the claustrum acts as an integrative relay across multiple brain networks.
“This network account explains clinical features of stuttering such as motor timing difficulties in speech and the pronounced sensitivity of symptom severity to emotional state,” Joutsa explains. “Because these structures sit at the intersection of motor control and emotion, their dysfunction can produce both speech disruption and variability with stress or anxiety.”
By locating stuttering within a reproducible neural network, the study provides a clearer neurobiological framework and suggests concrete targets for future interventions. The researchers highlight brain stimulation approaches that could be directed at the identified network as a promising therapeutic avenue to reduce stuttering.
About this research
Author: Tuomas Koivula
Source: University of Turku
Contact: Tuomas Koivula – University of Turku
Image credit: Neuroscience News
Original research (open access): “Localization of stuttering based on causal brain lesions” by Juho Joutsa et al., published in Brain.
Abstract
Localization of stuttering based on causal brain lesions
Stuttering affects about one in a hundred adults and can lead to significant communication difficulties and social anxiety. Most commonly it is a developmental condition, but stuttering can also be caused by focal brain damage, offering a unique window into the brain regions critical for fluent speech.
This study examined three independent datasets: (i) published case reports of acquired neurogenic stuttering after stroke (n = 20, ages 16–77); (ii) a clinical cohort of patients with acquired stuttering after stroke (n = 20, ages 45–87); and (iii) adults with persistent developmental stuttering (n = 20, ages 18–43). Using lesion network mapping on the first two datasets, the investigators tested whether diverse lesions that produced stuttering converge on a common functional network, and then assessed whether that lesion-derived network is relevant to developmental stuttering.
Lesions causing acquired stuttering were anatomically heterogeneous but were all functionally connected to a common network centered on the left putamen and including the claustrum, the amygdalostriatal transition area and adjacent regions. This pattern was specific to stuttering and replicated across both stroke datasets. Within this common network, grey matter volume in the left posteroventral putamen—extending into the claustrum and amygdalostriatal transition area—correlated with stuttering severity in adults with developmental stuttering.
The authors conclude that acquired neurogenic stuttering maps to a common brain network centered on the left putamen, claustrum and amygdalostriatal transition area, and that the overlap between this lesion-based network and structural differences in developmental stuttering supports a shared neuroanatomical basis across different causes of stuttering.