The first neurons that go to form the human cerebral cortex are generated during the first half of gestation in the proliferative ventricular zone close to the cavity of the cerebral ventricle. They undergo a complicated form of migration, termed the ‘inside-out’ pattern, in which the later born neuroblasts travel past those born earlier to the more superficial layers. After the crucial transition in cortical differentiation from mitotically active neuroblasts to postmitotic young neurons, the cortex begins to form radially-organized columns, the basic functional units for sensory processing and motor output that have been most studied in terms of touch-modality columns in the somatosensory cortex and orientation and ocular dominance columns in the primary visual cortex. Evidence of columnar organisation has been found in other cortical areas (e.g., primary auditory cortex, primary motor cortex), with the suggestion that it is also a characteristic of non-cortical areas (e.g., the brain stem and superior colliculus). It is thought that the expansion of the cortex that becomes strikingly evident some 4 months after conception is due to increases in the number of columns rather than from increases in the sizes of individual columns. Furthermore, it is hypothesised that columnar development is driven by a process of activity-dependent self-organization. There are two major growth spurts. The first occurs during the eighteen months following birth, and consists of mainly motor and sensory projections, and the second prior to puberty at about 11 years in girls and 12 years in boys, mainly in the frontal cortex and tertiary overlapping areas. Other age-related morphometric studies of the cerebral cortex in humans show developmental changes continuing into adolescence, especially with regard to the frontal cortex. Interneuronal connectivity develops rapidly during infancy and early childhood, with excess synaptic connections being eliminated.
See Activity-dependent organization, Axon retraction (or pruning), Brain stem, Cell migration, Cerebellum (development), Cerebral cortex (or pallium), Cortical column, Frontal cortex, MRI morphometry, Neuroblasts, Neuronal migration disorders, Neurotransmitters, Primary motor cortex, Primary visual cortex (V1), Proliferative ventricular zone, Self-organization, Superior colliculus, Synapse elimination, Synaptogenesis, Ventricle