Title: Microstructural changes in the posterior associative cortex in children during the first year of life
Abstract: The aim of the study was to study of age-related changes in cytoarchitectonics in functionally different areas of the posterior associative cortex in the temporal and occipital lobes of the cerebral hemispheres in children during the first year of life. Material and methods. The study material included left hemispheres of male children (39 observations) aged from birth to 12 months who died in accidents without brain damage. Using computer morphometry, the thickness of the cortex, the thickness of the external pyramidal layer and the area of the profile field of pyramidal neurons were measured on Nissle stained frontal histological sections of the cortex taken in the temporo-parietaloccipital subfield (subfields 37a, 37a, 37d) and field 19 of the occipital region, which are jointly part of the posterior associative cortex. Quantitative data were analyzed at monthly intervals. Results. The thickness of the posterior associative cortex in infants on the lateral surface of the temporal and occipital lobes increased by 3, 6, and 9 months; on the inferior medial and medial surfaces of the temporal lobe, by 5 and 12 months. Significant increases in the cross section of layer III occurred simultaneously: in subfield 37as by 2 and 6 months, in subfield 37a by 3 and 8 months, in subfield 37d by 2 and 5 months, and in field 19 by 3 and 9 months. All of the studied neocortex zones were characterized by two-stage cortical growth in thickness, as well as a faster rate of increase in the thickness of layer III in relation to the total cortical cross section, relative stability in the size of pyramidal neurons in sublayer III3 from birth to 3 months and their intense increase from 3 to 8-9 months. Conclusion. Microstructural changes in different fields of the posterior associative cortex have significant differences, which are reflected in the age-related dynamics of the thickness of the cortex and associative layer III, as well as the size of the pyramidal neurons. The most significant structural and functional changes in these parameters are noted from 3 to 5 months and from 8 to 9 months, as well as by the end of the first year of life.