Concordant anatomical and functional connectivity changes in developmental stuttering

Abstract

Stuttering is based on a maldevelopment of speech-relevant brain regions and is associated later in life with left perisylvian grey and white matter anomalies and right-hemispheric functional compensation attempt. We hypothesized that in adult stutterers left-hemispheric structural anomalies alter the functional connectivity of the speech production network which prompts stutterers to use right-hemispheric strategies to reduce symptoms. To study anatomical and functional connectivity during overt reading, we performed a structural (DTI) and functional (EPI) study on 13 male adult stutterers and 13 male matched fluent control subjects. Anatomical connectivity was assessed by comparing values of fractional anisotropy using TBSS for FSL and functional connectivity was studied by comparing psychophysiological interactions for overt>covert reading in SPM. Anatomical connectivity changes were restricted to the left hemisphere: We confirmed (Sommer et al., Lancet 2002) an FA reduction below the somatomotor representation of articulation and found pathologically enhanced FA values in fibre tracts below the left inferior frontal gyrus, anterior insula and in the anterior segment of the arcuate fasciculus. The increases and decreases of anatomical connectivity were accompanied by similar changes in functional connectivity of the corresponding brain regions: Functional connectivity during overt>covert reading was reduced between the articulatory motor cortex and the superior temporal gyrus while it was enhanced between the inferior frontal and the supramarginal gyrus compared to fluent controls. We interpret the concordant alterations in functional connectivity in adult stutterers as a consequence of pathological anatomical connectivity on the basis of a left perisylvian maldevelopment in early childhood. Thus, linking comparative analyses of anatomical and functional connectivity helps understanding how structural pathology translates into dysfunction.