DTI data. FA threshold for line tracking was set to 0.2. The maximum angle threshold was 50°. We performed tractography using the two‐regions‐of‐interest (ROIs) approach. In recent years, analyses have been carried out by segmenting CC fibers using a two‐ROIs approach into multiple regions based on the cortical regions that the CC projects to (Huang et al., 2005; Lebel, Caverhill‐Godkewitsch, & Beaulieu, 2010). One of our previous studies applied that technique in mood disorder investigations (Yamada et al., 2015). The first reference ROI was focused on the CC in a midsagittal slice, and secondary ROI was seven separate cortices spanning both sides of the midline (Appendix S1). As seen in Figure 1, callosal fibers were separated into seven segments based on their cortical projection zones. Ordered from front to back, the seven sections were as follows: orbital frontal, anterior frontal, superior frontal, superior parietal, posterior parietal, temporal, and occipital. All ROIs were drawn in accordance with specific anatomical landmarks and guidelines that were followed carefully and consistently for all patients (Figure 2). Same as the previous studies (Brandstack, Kurki, Laalo, Kauko, & Tenovuo, 2016; Huang et al., 2005; Lebel et al., 2010), fibers that were clearly not part of the
