Pathways connecting limbic areas form earlier in development.

(A) Sketch of the right hemisphere (medial view) showing the major white matter tracts (green lines) in the human brain (redrawn from Fig 751 in [27]). Tracts connecting limbic areas (cingulate bundle and uncinate fasciculus) are curved and tracts connecting eulaminate areas (superior and inferior longitudinal fasciculi) are straight. (B) Formation of the temporal, occipital, and frontal poles in development (redrawn from Fig 11.4 in [1]). Early in development (left panel), there is an early posterior pole (orange). As the neocortex expands (middle panel), the early posterior pole is pushed anteriorly and ventrally to its final location; the temporal pole is composed of areas that are displaced with the early posterior pole (right panel). We propose that the axons of the cingulate bundle (green line in the three panels) and the uncinate fasciculus arrive to the subplate of their target areas early in development and are curved by the displacement of the early posterior pole to its final location. ac, anterior commissure; cc: corpus callosum.