Altered cingulum bundle microstructure in autism spectrum disorder.

OBJECTIVE Here, we examined the cingulum bundle, a long-range white matter tract mediating dorsal limbic connectivity, using diffusion tensor imaging (DTI) tractography, in children and adolescents with autism spectrum disorder (ASD) versus controls. We hypothesised that cingulum bundle microstructure would be altered in ASD, based on evidence implicating abnormal white matter connectivity in this disorder. METHODS DTI data were acquired for 19 ASD participants (IQ ⩾ 70; 7-18 years; mean = 12.4 ± 3.1) and 16 age-matched controls (7-18 years; mean = 12.3 ± 3.6) on a 3 T magnetic resonance imaging system. Deterministic tractography was used to isolate the cingulum bundle. Left and right cingulum bundles were examined for differences in several DTI metrics in ASD children/adolescents versus controls, including: fractional anisotropy (FA), mean, axial, and radial diffusivity. RESULTS Significant age × group interaction effects were found for all DTI metrics (mean diffusivity: F 1,28 = 9.5, p = 0.005, radial diffusivity: F 1,28 = 7.8, p = 0.009, axial diffusivity: F 1,28 = 5.2, p = 0.03, FA: F 1,28 = 4.4, p = 0.04). Interaction effects were driven by increases in cingulum bundle diffusivity (mean, radial, and axial diffusivity), and decreased FA, in younger ASD participants within our sample versus controls. CONCLUSION Our results point to immature microstructural organisation of the cingulum bundle in ASD, particularly during the early years of life, with implications for limbic network synchronisation and complex socio-emotional performance.