title: The trajectory of gray matter development in Broca's area is abnormal in people who stutter.
abstract: The acquisition and mastery of speech-motor control requires years of practice spanning the course of development. People who stutter often perform poorly on speech-motor tasks thereby calling into question their ability to establish the stable neural motor programs required for masterful speech-motor control. There is evidence to support the assertion that these neural motor programs are represented in the posterior part of Broca's area, specifically the left pars opercularis. Consequently, various theories of stuttering causation posit that the disorder is related to a breakdown in the formation of the neural motor programs for speech early in development and that this breakdown is maintained throughout life. To date, no study has examined the potential neurodevelopmental signatures of the disorder across pediatric and adult populations. The current study aimed to fill this gap in our knowledge. We hypothesized that the developmental trajectory of cortical thickness in people who stutter would differ across the lifespan in the left pars opercularis relative to a group of control participants. We collected structural magnetic resonance images from 116 males (55 people who stutter) ranging in age from 6 to 48 years old. Differences in cortical thickness across ages and between patients and controls were investigated in 30 brain regions previously implicated in speech-motor control. An interaction between age and group was found for the left pars opercularis only. In people who stutter, the pars opercularis did not demonstrate the typical maturational pattern of gradual gray matter thinning with age across the lifespan that we observed in control participants. In contrast, the developmental trajectory of gray matter thickness in other regions of interest within the neural network for speech-motor control was similar for both groups. Our findings indicate that the developmental trajectory of gray matter in left pars opercularis is abnormal in people who stutter.
authors.affiliation: Department of Communication Sciences and Disorders and the Institute for Stuttering Treatment and Research, Faculty of Rehabilitation Medicine, University of Alberta Edmonton, AB, Canada ; Neuroscience and Mental Health Institute, University of Alberta Edmonton, AB, Canada.
authors.forename: Deryk S
authors.initials: DS
authors.lastname: Beal
authors.affiliation: Program in Neuroscience and Mental Health, The Hospital for Sick Children Toronto, ON, Canada ; Department of Medical Biophysics, University of Toronto Toronto, ON, Canada.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Lerch
authors.affiliation: Department of Communication Sciences and Disorders and the Institute for Stuttering Treatment and Research, Faculty of Rehabilitation Medicine, University of Alberta Edmonton, AB, Canada.
authors.forename: Brodie
authors.initials: B
authors.lastname: Cameron
authors.affiliation: Department of Communication Sciences and Disorders and the Institute for Stuttering Treatment and Research, Faculty of Rehabilitation Medicine, University of Alberta Edmonton, AB, Canada.
authors.forename: Rhaeling
authors.initials: R
authors.lastname: Henderson
authors.affiliation: Haskins Laboratories New Haven, CT, USA ; Centre for Research on Brain, Language and Music, McGill University Montreal, QC, Canada.
authors.forename: Vincent L
authors.initials: VL
authors.lastname: Gracco
authors.affiliation: Department of Speech-Language Pathology, University of Toronto Toronto, ON, Canada.
authors.forename: Luc F
authors.initials: LF
authors.lastname: De Nil
keywords: Broca’s area; cortical thickness; developmental disorders; developmental stuttering; inferior frontal gyrus; motor control; neurodevelopment; speech production