Adjusting for presumed earlier maturity in females by comparing females with boys who were approximately two years older resulted in even more pronounced effects with the exception of the splenium, where the effects size of the difference decreased. As increases in FA and decreases in mean diffusivity with development had been reported in a similar population by this group as well as others, the finding of greater FA values in males, despite their later maturation, suggested that sexually dimorphic processes are at work beyond differences in maturational rates. The authors speculated that this may be related to more extensive fiber crossing in females. A study in 21 adolescents (9 male, mean age 12.3 +- 2.9yrs) also found that males overall had higher FA values in left frontal WM regions than females (Silveri et al., 2006). These results are different than those found in a study in adults, which reported greater anisotropy in frontal regions in females (Szeszko et al., 2003). It is possible that relative anisotropy values in males and females may change as maturation completes, a question awaiting the
