Connectivity deficit in the corpus callosum (CC), a major fiber system linking the two hemispheres, following delayed migration of a subset of cortical neurons. Schematic drawing shows that labeled neurons in the ipsilateral hemisphere (IPSI) send their axonal projections to the contralateral hemisphere (Contra). These so-called commissural fibers arborize and establish synaptic contacts in specific cortical layers (L2/3 and L5A). The upper row of images illustrate the situation in a control rat with normal neuronal migration. We can see high density of commissural fibers in the contralateral hemisphere at postnatal day 14. On the lower row of images show in a rat with delayed neurons there is a reduced density of commissural fibers in the contralateral hemisphere. © Bocchi et al. Nature Communication 2017, Fig 4. C.