We present a set of hypotheses about the biologic mechanisms of lateralization, ie, the processes which lead to an asymmetrical nervous system. It would have been difficult even 20 years ago to formulate such a theory in the face of the prevalent belief that cerebral dominance lacked an anatomic correlate. It is proposed that cerebral dominance is based in most instances on asymmetries of structure. Although genetic factors are important we will lay stress on sever
See also pp 427 and 500.
al factors that, in the course of development, both prenatal and postnatal, modify the direction and extent of these structural differences. Special attention will be directed to the intrauterine environment as a determinant of the pattern of asymmetries, and in particular sex hormones, eg, testosterone or related factors. We will discuss the associations of anomalous cerebral dominance which include not only developmental disorders such as dyslexia and certain