Age-related changes in the microstructural organization of the human posterior associative cortex from birth to 12 years

The aim was to study age-related changes in cytoarchitecture in functionally differentiated zones of the posterior associative cortex in the temporal and occipital lobes of the cerebral hemispheres in children from birth to 12 years of age. Materials and Methods. The study material included 73 left cerebral hemispheres of male children from birth to 12 years of age who died as a result of an accident. Computerized morphometry was used to measure cortical thickness, outer pyramidal plate thickness, and pyramidal neuron profile field area on Nissl-stained paraffin sections of the cortex taken in the temporoparietal-occipital subarea (subareas 37ac, 37a, 37d) and area 19 of the occipital region. Quantitative data were analyzed at annual intervals. Results. The thickness of the posterior associative cortex in children increased on the lateral surface of the temporal and occipital lobes at 1, 4, and 7 years, on the inferior medial surface of the temporal lobe at 1 and 6 years, and on its medial surface at 1 and 7 years. The significant increase in layer III thickness in subareas 37ac, 37a and 37d occurred synchronously with the increase in cortical cross-sectional area, and in area 19 it continued from 4 to 7 years after the stabilization of the group-average indicators of cortical thickness in this field. All areas examined were characterized by a two-step growth of cortical thickness, which exceeded the growth rate of layer III thickness in relation to total cortical cross-section. The size of pyramidal neurons in subareas 37ac and 37d increased in two stages, while those in subarea 37a and area 19 increased in three stages of different duration. Conclusions. Microstructural changes in the posterior associative cortex in children are heterochronic, heterodynamic, and specialized not only in topographically and functionally distinct cortical areas, but also in separate cytoarchitectonic fields, subfields, and at the level of cytoarchitectonic layers and intracortical microstructural components. The most significant morphofunctional transformations are observed during the first year of life, as well as at 3-4, 6-7, and 10 years of age.