A highly significant negative correlation was observed for the place ( r = −0.6, P < 0.001) condition (Fig. 3 a), indicating that participants that performed better with the left hand had larger volume of the right SLF I (compared with the left SLF I), while those who performed better with the right hand had larger volume of the left SLF I (compared with the right SLF I).
When the analysis was repeated for each handedness group separately, the relationship between volume asymmetry of the SLF I and lateralization of performance in the pegboard test was significant only for the right-handers ( r = −0.542, P < 0.05) in the place condition with a trend towards significance also for the left-handers ( r = −0.545, P = 0.06).
Of the 5 variables, only the LI of the SLF I was significantly associated with handedness ( P = 0.003; see Supplementary Table S1 ), although SLF II tract asymmetry approached significance ( P = 0.064).