Abstract: In this experimental study of conditioned reflex to simultaneous and successive complex stimuli, three age groups (9, 12, 15) of children were studied. The results show the age characteristics in the analytical synthetic activities of children's higher central nervous system:1) In the process of formation of conditioned reflexes to the complex stimuli, it was found that the younger the child, the easier it reacted in motor reactions toward the presented single element of a complex stimulus (especially to the last element of successive complex stimuli). In other Words, the synthetic activities of these children are not fully developed.2) The formation of differential inhibition has an active influence on the synthetic activities of the cerebral cortex, and in the two older groups the active influence is clearer than that in the 9 year old age group, in which the process of inhibition is not so concentrated.3) The older the children, the more correctly they can react to the complex stimuli, as regards both motor reactions and their relationship in the second signal system.The formation of differentiation in active influence on the synthetic process is also reflected in the second signal system.

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