The corpus callosum (CC) is the most prominent white matter structure and easily visualized on mid sagittal MR images. The CC consists of approximately 200 million mostly myelinated axons connecting homologous areas of the left and right cerebral hemispheres. The functions of the CC can generally be thought of as integrating the activities of the left and right cerebral hemispheres, including functions related to the unification of sensory fields (Berlucchi 1981; Shanks et al. 1975), memory storage and retrieval (Zaidel and Sperry 1974), attention and arousal (Levy 1985) and enhancement of language and auditory functions (Cook 1986). In agreement with several studies that have indicated increasing CC size during adolescence (Allen et al. 1991; Cowell et al. 1992; Pujol et al. 1993; Rauch and Jinkins 1994; Thompson et al. 2000), total midsagittal CC area increased robustly from ages 4–20 years in the CPB sample (Fig. 2e).
