The Neurobiological Grounding of Persistent Stuttering: from Structure to Function

Area of Science:

• Neuroscience
• Speech and Language Pathology
• Neuroimaging

Background:

• Chronic persistent stuttering is a complex speech disfluency with underlying neuronal mechanisms.
• Previous research suggests disrupted white matter connectivity and altered brain activation in individuals who stutter.

Purpose of the Study:

• To highlight robust findings on the neurobiology of stuttering using meta-analyses of neuroimaging studies.
• To integrate findings from diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI) with transcranial magnetic stimulation (TMS) data.

Main Methods:

• Meta-analysis of diffusion tensor imaging (DTI) studies investigating white matter integrity in persistent stuttering.
• Review of functional magnetic resonance imaging (fMRI) meta-analyses on brain activation patterns during stuttering and fluent speech.
• Integration of transcranial magnetic stimulation (TMS) findings on cortical dynamics in speech motor areas.

Main Results:

• Meta-analysis of DTI studies consistently showed reduced fractional anisotropy in the left dorsal stream and interhemispheric sensorimotor connections.
• fMRI meta-analyses linked stuttering to reduced left fronto-parieto-temporal activation, while fluency correlated with right-sided co-activation.
• TMS revealed reduced speech-planning neuronal dynamics in the primary motor cortex of individuals who stutter.

Conclusions:

• Neuroimaging and TMS collectively indicate disrupted white matter connectivity and aberrant cortical dynamics as key neurobiological features of stuttering.
• Future research should focus on the dynamic interactions between auditory, somatosensory, and speech motor circuits to understand fluent speech production.