For the average myelin content of areas 4 [L] and p24' [R] (where [L] denotes left and [R] denotes right), the multiple mediation model (Figure 1) measured the indirect effects, which are defined by the path from age to the regional myelin score (Figure 1, ax) and from the regional myelin score to the pegboard score (Figure 1, bx). The proportion of the indirect effects of area 4 [L] was about twice as large as that of area p24' [R] for the dominant hand (28% for 4 [L] and 14% for p24' [R]) but had similar effects for the non-dominant hand (24% for 4 [L] and 22% for p24' [R]) (Table 4).
