On the cause of stuttering: Integrating theory with brain and behavioral research

Stuttering is present in all cultures with a prevalence of around 1%. While there has been extensive brain and behavioral research into stuttering over the last 50 years, its cause remains unknown. Brain imaging research has shown anomalous activations during stuttered speech and, more recently, has identified structural anomalies in the speech language areas of the brain. A recent meta-analysis concluded that these aberrant neural activations are a consequence of stuttering rather than a cause, and that stuttering is a disorder of the initiation of speech motor plans. Expanding on this hypothesis we propose that this disorder comprises the initiation of syllables. We provide evidence that this is underpinned by a disturbance of neural function in SMA. Our syllable initiation (SI) theory has evolved from our working model, the variability or Vmodel. SI theory draws not only on brain research in stuttering but also on research into speech production deficits after brain damage. SI theory locates stuttering at the interface of speech and language and we suggest that it provides a plausible and parsimonious explanation of the cause and critical phenomena of stuttering.