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Cytoarchitectonics of motor speech areas 44 and 45 of human brain was studied during postnatal ontogeny. Hemispheric asymmetry of some cytoarchitectonic indexes and volumes of the cortex and the number of neurons in these structures was revealed. The presence of stable and unstable types of morphological markers of hemispheric asymmetry in human brain that change the sign of asymmetry during various periods of ontogeny is hypothesized. Key Words: human brain; asymmetry; ontogeny; cytoarchitectonicsInterhemispheric asymmetry of the brain first studied by P. Broca [6] and other investigators is still of considerable interest. The left hemisphere is involved in speech functions, and the right hemisphere plays the major role in spatial and temporal processes. Functional asymmetry of the brain and neuronal organization of the right and left hemispheres are extensively studied. However, the problem of structural asymmetry of human brain received little attention. There are only few reports concerning the asymmetry of macroscopic structures of human brain and some cytoarchitectonic areas [1][2][3][4][5]7,9]. The following questions remain unclear: which structural signs characterize functional asymmetry of the brain, when they are formed during ontogeny, and whether all cytoarchitectonic markers reflect the interhemispheric lateralization of brain functions?Here we studied structure and development of motor speech areas 44 and 45 and the motor speech region of the left and right cerebral hemispheres during postnatal ontogeny. Particular attention was given to specific cytoarchitectonic features of Broca's areas in the left and right hemispheres, volumes of motor speech areas 44 and 45. and the number of neurons in these regions at various ages. MATERIALS AND METHODSSerial frontal slices of brain hemispheres of a neonate, children (2, 7, and 12 years), and 30-year-old adult were examined. A total of 11 brains (22 hemispheres) were examined. Slices (20 p thick) were stained with cresyl violet by a modified procedure (Institute of Brain). Each 40th or 80th slices were examined. The volume of structures and the number of neurons were determined by stereological methods proposed by H. B. M. Uylings [8,10]. The coefficient of tissue shrinkage was considered during the quantitative analysis of results. Boundaries between motor speech areas and adjacent structures were determined using an MBS-9 microscope and then transferred to slice projections. Topographic cytoarchitectonic maps of areas 44 and 45 were reconstructed on the lateral surface of cerebral hemispheres.

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