is to support voluntary saccades (Vogt 2016), control over which is critical for eye-hand coordinated movement needed for successful grooved pegboard performance. The complementary relation of unimodal (area 4) and multimodal (areas p24' and 23c) cortices between normalized myelin content and function is consistent with the hypothesis that heavy myelination (as in area 4) occurs with simple circuitry (used for speed), whereas lighter myelination occurs with greater intracortical circuit complexity (used for purposefully directed movement). Coordination of such different levels of circuit complexity continues to develop throughout adolescence, and the unimodal/multimodal complementary microstructural changes may represent active synaptic tuning, pruning, and functional development towards an asymptote in young adulthood.
