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English: Increase in brain size and the maturation of cortical circuits. The maturation of mental processes and motor skills is associated with an approximately four-fold enlargement in brain size [1]. A., B. Photographs of the brains of a 1-month and 6-year-old child, respectively. This size increase is accompanied by a dramatic development in the complexity of the neuronal processes, which in turn is influenced by the genetic background and the surroundings. This increase in the complexity is clearly evident in the drawings of Golgi-stained cortical neurons from the cerebral cortex of a 1-month-old child (C. showing the cortical area known as “pars triangularis of gyrus frontalis inferior”; D. showing “orbital gyrus”) and a 6-year-old child (E. “pars triangularis of gyrus frontalis inferior”; F. “orbital gyrus”). Scale bar for A and B: 2 cm.