0362-1197/01/2705- $25.00 © 2001 MAIK “Nauka /Interperiodica” 0544 Human Physiology, Vol. 27, No. 5, 2001, pp. 544–550. Translated from Fiziologiya Cheloveka, Vol. 27, No. 5, 2001, pp. 41–48. Original Russian Text Copyright © 2001 by Tsekhmistrenko, Vasil’eva. It is well known that the most complex integrative processes in human cortex involve the frontal and cau- dal associative zones, controlling intersensory analysis and programming the adaptive behavioral responses in a changing environment [1]. These brain regions are involved in the higher integrative functions of cognition [2]. It is also known, that various areas of the human brain mature heterochronously, and the associative zones are characterized by the most prolonged and complex structural modifications [3]. To analyze the age-related patterns of postnatal development of the late-maturing areas of human cor- tex, we examined microstructural modifications of the temporo–parieto–occipital subregion of the neocortex (fields 37a, 37ac, and 37d of the caudal associative zone), which play significant roles in the perception and recognition of complex visual patterns. The tem- poro–parieto–occipital subregion, in addition to the lower occipital area, works as a higher integrating cen- ter in the analysis of visual information [4]. We also studied postnatal modifications of the structural organi- zation of the cortex, the frontal lobe, in field 8 (oculo- motor), 44 (speech motor), and 32/10 (adjacent to the limbic area, involved in psychoemotional processes) of the frontal associative area. The existing studies of frontal and caudal associative zones are relatively few and involve a limited number of subjects [5–7]. METHODS The materials of this study consisted of 124 brain hemispheres of practically healthy children, adoles- cents and young adults, from neonates to 20 years of age, who died of various causes not associated with brain injury. The material was grouped according to the years, as required by the study. For the cytological anal- ysis, samples of cortex were taken from fields 37a, 37ac, 37d, 8, 44, and 32/10 indicated in [8]. The histo- logical preparations were stained with cresyl purple following Nissl, impregnated with silver nitrate using the methods of Peters and Golgi. The analysis of the preparations was done using the computer imaging sys- tem, including a Biolam L-211 light microscope, a computer with a display, a video camera, and a special video card. Image analysis was performed with Bios- can-AT computer software, with the same optical and metric characteristics used for all preparations. Mor- phometry included measurement of the area of the pro- file fields of neurons in the ensemble-forming layers III and V of the cortex, and nest-type cellular groups in the sublayer III 3 . Using an eyepiece micrometer, we mea- sured the thickness of the cortex, its layers and sublay- ers in the frontal sections at the top of the convolution. To determine the age-related modifications of neurons and their groups, we used the basic statistics package Biotest of the package Bioscan-AT and other statistical methods [9–12]. Structural Transformations of the Associative Cortex As the Morphological Base of the Development of Human Cognitive Functions from Birth to 20 Years of Age T. A. Tsekhmistrenko and V. A. Vasil’eva Institute of Age Physiology, Russian Academy of Education, Russia Received April 11, 2001 Abstract—The microstructure of the temporo-parieto-occipital subregion and the frontal area of the brain from birth to 20 years of age was studied using computer morphometry. These brain zones are involved in the higher integrative mechanisms of cognitive functioning in children, adolescents and young adults. Structural transfor- mations of the cortex represent a stage-by-stage process. Each stage in the frontal and occipital associative zones has specific temporal limits and is characterized by the quantitative and qualitative specificity of the mor- phological changes at each of the system levels considered: neuronal, modular, and stratification. The structural modifications from birth to early adulthood are primarily associated with the final development of micro and macroassembles and their structural components, primarily, neurons of various types. The growth and differen- tiation of neurons involves heterochrony with respect to the terms and developmental rates in the frontal and occipital associative cortex. The terms of the most active synchronous postnatal structural modifications, occur- ring during the first year of life, during the years 2–3, 6–7, 9–10, and 13–14 were analyzed. It was shown, that local specialization of cellular ensembles at various levels is a consequence of the functional specialization of microensembles, involved in cortical information processing, including cognitive activity and other higher psy- chophysiological functions of the human brain.