Higher brain functions rely on functional units such as laminated structures and nuclei. To construct these structures, postmitotic neurons migrate from their sites of origin to their final destinations. Most CNS neurons are generated in the ventricular zone of the neural tube and then migrate radially towards the pial surface. Birthdate-dependent settlement followed by radial migration leads to the establishment of laminated structures such as the cerebral cortex. Neuronal migration also occurs in tangential directions. Although occurrence of tangential migration (TM) has been known for a long time, significance of TM has recently begun to be elucidated. A good example can be found in the cerebral cortex: here the excitatory neurons are born in the ventricular zone, and then migrate to the cortical plate (CP). On the other hand, inhibitory interneurons are generated in the basal forebrain and migrate tangentially to the CP. As a result, a structure with mixed excitatory and inhibitory neurons is established. TM of neurons also contributes to nucleogenesis. For example, neurons that are destined to form precerebellar nuclei originate from the lower rhombic lip, migrate circumferentially and then, they change the direction of migration from tangential to radial. These neurons eventually terminate radial migration at a distance from the pial surface to form nuclei (Kawauchi et al., 2006). Thus, nucleogenesis is a consequence of successive occurrence of TM and radial migration. Real time imaging further elucidates additional interesting features of TM. This will be shown with the aid of movies. [J Physiol Sci. 2007;57 Suppl:S3]
