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

Abstract

BACKGROUND: Human posterior associative cortex, including its temporoparietal–occipital subarea, is important in cognitive control, verbal activity, sensory stimuli processing, and attention regulation, visuomotor responses, and situational decision making. Despite data suggesting the prolonged formation of these higher mental functions during postnatal ontogeny, the posterior associative cortex has been insufficiently characterized with respect to microstructural transformations in its individual functionally specialized zones during childhood development. AIM: This study aimed to examine age-related changes in the cytoarchitecture of functionally differentiated zones of the posterior associative cortex in the temporal and occipital lobes of the cerebral hemispheres from birth to 12 years of age. MATERIALS AND METHODS: The study analyzed 73 left cerebral hemispheres of male children from birth to age 12 years who died because of an accident. Computerized morphometry was employed 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, and 37d) and area 19 of the occipital region. Quantitative data were analyzed at annual intervals. RESULTS: The thickness of the posterior associative cortex increased on the lateral surface of the temporal and occipital lobes at the ages of 1, 4, and 7 years; on the inferior medial surface of the temporal lobe at the ages of 1 and 6 years; and on its medial surface at the ages of 1 and 7 years. The layer III thickness in subareas 37ac, 37a, and 37d significantly increased synchronously with the increase in cortical cross-sectional area, and in area 19, it continued from the age of 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 the total cortical cross-section. The size of the pyramidal neurons in subareas 37ac and 37d increased in two stages, whereas those in subarea 37a and area 19 increased in three stages of different durations. 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 level of cytoarchitectonic layers and intracortical microstructural components. The most significant morphofunctional transformations are observed during the first year of life and at the ages of 3–4, 6–7, and 10 years.