Evidence of Left Inferior Frontal–Premotor Structural and Functional Connectivity Deficits in Adults Who Stutter

Abstract

The neurophysiological basis for stuttering may involve deficits that affect dynamic interactions among neural structures supporting fluid speech processing. Here, we examined functional and structural connectivity within corticocortical and thalamocortical loops in adults who stutter. For functional connectivity, we placed seeds in the left and right inferior frontal Brodmann area 44 (BA44) and in the ventral lateral nucleus (VLN) of the thalamus. Subject-specific seeds were based on peak activation voxels captured during speech and nonspeech tasks using functional magnetic resonance imaging. Psychophysiological interaction (PPI) was used to find brain regions with heightened functional connectivity with these cortical and subcortical seeds during speech and nonspeech tasks. Probabilistic tractography was used to track white matter tracts in each hemisphere using the same seeds. Both PPI and tractrography supported connectivity deficits between the left BA44 and the left premotor regions, while connectivity among homologous right hemisphere structures was significantly increased in the stuttering group. No functional connectivity differences between BA44 and auditory regions were found between groups. The functional connectivity results derived from the VLN seeds were less definitive and were not supported by the tractography results. Our data provide strongest support for deficient left hemisphere inferior frontal to premotor connectivity as a neural correlate of stuttering.

Birth weight and stuttering: Evidence from three birth cohorts

“…Packman (2012) has proposed a model of developmental stuttering whose central hypothesis is that the fundamental cause of the disorder is a neural deficit. This hypothesis is consistent with the findings of many recent studies which have reported structural and functional abnormalities in the brains of people who stutter (Chang, Erickson, Ambrose, Hasegawa-Johnson & Ludlow, 2008;Chang, Horwitz, Ostuni, Reynolds & Ludlow, 2011;Cykowski, Fox, Ingham, Ingham & Robin, 2010;Watkins, Smith, Davis & Howell, 2008). One risk factor for abnormal neural development is birth weight (Walhovd, Fjell, Brown, et al, 2012).…”

How Stuttering Develops: The Multifactorial Dynamic Pathways Theory

“…Anatomical studies using diffusion tensor imaging in AWS have been used to measure the fractional anisotropy (FA, an index reflecting the fiber coherence or efficiency of conduction of white matter tracts) of the tracts connecting the left premotor area to primary motor areas involved in articulation. Results of these studies suggest deficits in connectivity between these critical areas for speech production and in perisylvian tracts important for auditory/motor integration in individuals who stutter (Chang, Horwitz, Ostuni, Reynolds, & Ludlow, 2011;Cykowski, Fox, Ingham, Ingham, & Robin, 2010;Sommer, Koch, Paulus, Weiller, & Büchel, 2002). A recent study examined the frontal aslant tract, which connects the inferior frontal gyrus with the supplementary motor area and the pre-supplementary motor area and found evidence of atypical structure of this important part of the motor pathway for speech bilaterally in AWS (Kronfeld-Duenias, Amir, Ezrati-Vinacour, .…”

Speaking-related changes in cortical functional connectivity associated with assisted and spontaneous recovery from developmental stuttering

“…Comprehensive interpretation of recovery-associated changes indeed requires taking into account changes at the level of inter-regional functional connectivity. Several functional connectivity studies have already been performed in PS, either during speaking (Chang, Horwitz, Ostuni, Reynolds, & Ludlow, 2011;Lu et al, 2010;Watkins, 2011) or while resting silently inside the scanner (Lu et al, 2012;Sitek et al, 2016,Yang, Jia, Siok, & Tan, 2016. Both approaches have their advantages and drawbacks.…”