White matter connectivity between superior temporal sulcus and amygdala is associated with autistic trait in healthy humans.

Growing evidence suggests that autistic traits, such as reduced social and communication skills, exist along a continuum between healthy and pathological conditions. Thus, functional and structural investigations of neuroanatomical substrates that significantly correlate with autistic tendency in healthy human subjects are critical for understanding this disorder. To accomplish this goal, we performed functional magnetic resonance imaging (fMRI) in combination with diffusion tensor imaging (DTI) in 30 healthy young subjects. The subjects were evaluated using the Autistic-Spectrum Quotient (AQ), which was designed to measure autistic traits in healthy and autistic spectrum disorder (ASD) subjects. Face-specific brain activation in the superior temporal sulcus (STS) and amygdala (AMG) was identified using fMRI and passive viewing of faces. In addition, probabilistic tractography performed in each subject by using DTI showed a white matter pathway between the face-specific regions of interest in the STS and AMG. The volume of connectivity between the STS and AMG correlated positively with the total AQ score (Spearman's ρ=0.38, p<0.05); however, among the AQ subscales, only imagination was significantly associated with the connectivity volume. These results suggest that healthy subjects with high autistic traits may show an increase in the white matter pathway that connects key regions involved in face processing.