The Neurobiological Grounding of Persistent Stuttering: from Structure to Function

Abstract

Neuroimaging and transcranial magnetic stimulation provide insights into the neuronal mechanisms underlying speech disfluencies in chronic persistent stuttering. In the present paper, the goal is not to provide an exhaustive review of existing literature, but rather to highlight robust findings. We, therefore, conducted a meta-analysis of diffusion tensor imaging studies which have recently implicated disrupted white matter connectivity in stuttering. A reduction of fractional anisotropy in persistent stuttering has been reported at several different loci. Our meta-analysis revealed consistent deficits in the left dorsal stream and in the interhemispheric connections between the sensorimotor cortices. In addition, recent fMRI meta-analyses link stuttering to reduced left fronto-parieto-temporal activation while greater fluency is associated with boosted co-activations of right fronto-parieto-temporal areas. However, the physiological foundation of these irregularities is not accessible with MRI. Complementary, transcranial magnetic stimulation (TMS) reveals local excitatory and inhibitory regulation of cortical dynamics. Applied to a speech motor area, TMS revealed reduced speech-planning-related neuronal dynamics at the level of the primary motor cortex in stuttering. Together, this review provides a focused view of the neurobiology of stuttering to date and may guide the rational design of future research. This future needs to account for the perpetual dynamic interactions between auditory, somatosensory, and speech motor circuits that shape fluent speech.

A Diagnostic Marker to Discriminate Childhood Apraxia of Speech From Speech Delay: IV. The Pause Marker Index

“…Momentary (within a few milliseconds) increases in amplitude of the inappropriate between-words abrupt pauses are consistent with deficits associated with state feedback control theory (Houde & Nagarajan, 2011), with possible control parameters including movement commands for respiratory, laryngeal, and articulatory targets. Phonatory behaviors as biomarkers of apraxia of speech, in particular, have attractive measurement features as they do in research in voice, dysfluency, and other motor speech disorders (e.g., Civier, Bullock, Max, & Guenther, 2013;Cohen, Renshaw, Mitchell, & Kim, 2016;Kim, 2015;Konopka & Roberts, 2016;Kumar, Croxson, & Simonyan, 2016;Ludlow, 2015;Neef, Anwander, & Friederici, 2015;Pouplier, Marin, & Waltl, 2014;Simonyan, 2013;Simonyan & Horwitz, 2011;Vanhoutte et al, 2014). In the present context, the same control mechanism underlying an abrupt inappropriate speech onset could underlie the excessive/equal sentential stress sign of CAS described previously.…”

Atypical brain activation in children who stutter in a visual Go/Nogo task: An ERP study

“…The less positive amplitudes on the right frontal area in CWS may reflect a lack of motor deactivation that would normally generate a positive deflection in the ERP wave in the Nogo condition (Smith et al, 2013). This would correlate with the documented over-activation of motor areas on the right side in adults who stutter (Belyk et al2015;Brown et al, 2005;Budde et al, 2014;Neef et al, 2015 ). This may be a compensatory means to overcome left-sided malfunctions in the motor control but perhaps also stimulus processing and inhibitory control.…”

“…The atypical distribution of brain activity in persons who stutter when compared to controls has been shown both in vocal tasks with fMRI or PET imaging ( Please, see meta-analysis by Belyk et al, 2015 andBudde et al, 2014 ) as well as in non-speech motor studies using TMS (Alm et al, 2013;Neef et al , 2011; see also review by Neef et al, 2015). Many recent studies have implied that the main problem lies in the connective white matter tracts of the brain rather than specific cortical areas.…”

“…This is often seen with simultaneous over-activation of right-sided areas such as right frontal operculum and pre-SMA (Belyk et al, 2015;Brown et al, 2005;Budde et al, 2014;Chang et al, 2009;Preibisch et al, 2003). Also non-speech motor function has been abnormally lateralized in recent transcranial magnetic stimulation studies in adults who stutter (Alm et al, 2013;Neef et al, 2011; see also review by Neef et al, 2015). Since the structural and functional aberrations in stuttering persons overlap structures relevant to inhibitory control (for an overview, see Chambers et al, 2009), the CWS could possibly show atypical lateralization of brain activity in an inhibitory task, as well.…”

How Stuttering Develops: The Multifactorial Dynamic Pathways Theory

“…Our understanding of the factors underlying chronic stuttering has been transformed by major advances over the past two decades in specifying the central neural correlates of stuttering in AWS (Neef, Anwander, & Friederici, 2015). Clear regions of interest for stuttering are left premotor and motor areas that are typically specialized for speech motor planning and production.…”