Reduced integrity in the frontal aslant tract's premotor connections is associated with dysfluency severity in stuttering.

Overview

1. Laboratoire Praxiling, UMR 5267—CNRS, Université Paul Valéry, Montpellier 34000, France
2. Department of Epilepsy, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, United Kingdom
3. Victor Horsley Department of Neurosurgery, National Hospital for Neurology and Neurosurgery, London WC1N 3BG, United Kingdom
4. Department of Neurosurgery, Gui de Chauliac Hospital, Montpellier University Medical Center, Montpellier 34295, France
5. Institut Universitaire de France, Paris 75005, France
6. Department of Medicine, University of Montpellier, Campus ADV, Montpellier 34090, France

Abstract

Stuttering is a neurodevelopmental disorder marked by impaired speech production and substantial interindividual variability in symptom severity. Although neuroimaging studies have identified abnormalities in the basal ganglia-thalamocortical circuitry, the specific white matter pathways that underpin dysfluent speech production remain poorly understood. Here, we focus on the frontal aslant tract (FAT), a dorsoventral intralobar tract connecting the superior and inferior frontal cortices and proposed to support both cognitive and motor functions. Using diffusion MRI, we first compared the quantitative anisotropy of the FAT and relevant control tracts in individuals who stutter (n = 30, mean age = 35.67, SD = 13.03) and fluent speakers (n = 22, mean age = 35.64, SD = 10.87) and observed no significant group-level differences in either hemisphere. To delineate the role of FAT subbundles in speech dysfluency, we then segmented the tract at its dorsal and ventral cortical terminations and assessed their relationships with stuttering severity (Stuttering Severity Instrument-Fourth Edition). We identified left FAT subbundles connecting the posteroventral frontal structures, particularly the rostroventral precentral gyrus and, to a lesser extent, the pars opercularis to a dorsal prefrontal region whose integrity predicts stuttering severity. The left-lateralized nature of these associations suggests that stuttering results, in part, from abnormal connectivity between prefrontal systems governing volitional control and the motor circuits engaged in speech production. Together, these findings refine current neurobiological models of stuttering by implicating frontofrontal white matter pathways underlying speech dysfluency and highlight a potential anatomical target for individualized therapeutic interventions.

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The codes used for statistical analyses are available on the Open Science Framework repository at https://doi.org/10.17605/OSF.IO/JMB6F. Due to the sensitive nature of the clinical and neuroimaging data involved, and because participants did not provide consent for unrestricted public access or general external sharing of raw data, the raw dataset cannot be made publicly available. However, access to pseudonymized individual-level data may be considered upon request from qualified researchers. Such access is contingent upon approval from the study sponsor/data controller. Additionally, it must comply with relevant French ethical and data protection requirements, including the General Data Protection Regulation and the provisions of the National Commission on Informatics and Liberty (CNIL). Where necessary, approval from the competent French Comité de Protection des Personnes will also be required (contact details: ; https://www.chu-toulouse.fr/comite-de-protection-des-personnes-cpp). Any granted access will necessitate the completion of an appropriate data-use agreement.

Reproduced under the paper's license (CC BY-NC), from the paper cited above.

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Recorded: type, language, journal, volume, issue, pages, dates, 9 authors, 5 keywords, 1 funder, 78 references.

Cite

This paper

Michon, M., Hirsch, F., Didirková, I., Giampiccolo, D., Monfrais-Pfauwadel, M.-C., Lemaitre, A.-L., Deverdun, J., Lebars, E., & Herbet, G. (2026). Reduced integrity in the frontal aslant tract's premotor connections is associated with dysfluency severity in stuttering. PNAS nexus, 5(7), pgag245. https://doi.org/10.1093/pnasnexus/pgag245

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