Abstract
Background: Prior brain imaging and autopsy studies have suggested that structural abnormalities of the basal ganglia (BG) nuclei may be present in Tourette Syndrome (TS). These studies have focused mainly on the volume differences of the BG structures and not their anatomical shapes. Shape differences of various brain structures have been demonstrated in other neuropsychiatric disorders using large-deformation, high dimensional brain mapping (HDBM-LD). A previous study of a small sample of adult TS patients demonstrated the validity of the method, but did not find significant differences compared to controls. Since TS usually begins in childhood and adult studies may show structure differences due to adaptations, we hypothesized that differences in BG and thalamus structure geometry and volume due to etiological changes in TS might be better characterized in children. Objective: Pilot the HDBM-LD method in children and estimate effect sizes. Methods: In this pilot study, T1-weighted MRIs were collected in 13 children with TS and 16 healthy, tic-free, control children. The groups were well matched for age. The primary outcome measures were the first 10 eigenvectors which are derived using HDBM-LD methods and represent the majority of the geometric shape of each structure, and the volumes of each structure adjusted for whole brain volume. We also compared hemispheric right/left asymmetry and estimated effect sizes for both volume and shape differences between groups. Results: We found no statistically significant differences between the TS subjects and controls in volume, shape, or right/left asymmetry. Effect sizes were greater for shape analysis than for volume. Conclusion: This study represents one of the first efforts to study the shape as opposed to the volume of the BG in TS, but power was limited by sample size. Shape analysis by the HDBM-LD method may prove more sensitive to group differences.
Highlights
Tourette syndrome (TS) is a chronic idiopathic syndrome characterized by the appearance of both vocal and motor tics during childhood or adolescence[1,2]
It has been suggested that problems with activity modulation in the basal ganglia and thalamus may contribute to the inability of Tourette Syndrome (TS) patients to exercise behavioral inhibition[5,6] as a result of these structures’ effects on behavioral inhibition via the prefrontal, parietal, temporal, and cingulate cortices[7]
Effect sizes (Cohen’s ƒ2) for both volume and shape are provided in Table 4; the effect sizes for the shape comparisons were larger than those for the volume comparisons
Summary
Tourette syndrome (TS) is a chronic idiopathic syndrome characterized by the appearance of both vocal and motor tics during childhood or adolescence[1,2]. Case studies of focal brain lesions have demonstrated new tic onset after lesions to the prefrontal cortex, thalamus, and basal ganglia[12]. Some TS patients have benefitted from deep brain stimulation of the globus pallidus and thalamus in TS13–16 These observations suggest a role for the basal ganglia, thalamus, and frontal cortex in tics. Prior brain imaging and autopsy studies have suggested that structural abnormalities of the basal ganglia (BG) nuclei may be present in Tourette Syndrome (TS). These studies have focused mainly on the volume differences of the BG structures and not their anatomical shapes.
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