The process of formation of functional asymmetry of the hemispheres, motor-sensory functions in ontogenesis. Lateralization (dominance) of the hemispheres is characterized by reciprocal and complementary interaction of the two hemispheres: in right-handed people, the left hemisphere is dominant, controlling speech functions, logical thinking, and the right hemisphere is subdominant, controlling the functions of perception and figurative thinking. Abnormal dominance of the hemispheres is represented by an equivalent interhemispheric interaction or a reversal of hemispheric dominance, when the right hemisphere becomes dominant. The process of formation of the dominance of the hemispheres goes in parallel with the dominance of the hand, leg, ear, eye, etc. Abnormal dominance of the hemispheres, arms, legs, ears, eyes, etc., can be a consequence of interhemispheric rearrangements as a result of their functional weakness.