[Ontogenic aspects of functional asymmetry of the hemispheres]

The use of one preferred hand for differentiated activities develops gradually and stabilizes at about the age of four years. Immediately after delivery the majority of infants turn spontaneously their head to the right and are able to perceive verbal stimuli and to respond to them by turning the head to the right. The recognition of verbal stimuli involves already in infants of 1-4 months the differentiation of different phonetic categories and perhaps also of bimodal and acoustic visual categories. The development of verbal functions end sat the 9th-12th year of life. The ontogenesis of functions of the right and left hemisphere is in addition to genetic factors influenced by perinatal cerebral lesions of various extent. During transmission of verbal functions from the left to the right hemisphere a more important part is played by plasticity than by the equipotentiality of the hemispheres. The right and left hemisphere develop at a different rate continuously, however, there are sudden developmental stages in some areas of the brain.