[Morphological correlates and heredity in functional asymmetry of the cerebral hemispheres]

Morphological findings which may be associated with asymmetric functions of the hemispheres have mostly appeared over the last two decades. They concern the leftsided dominance of the temporal plane and of the cytoarchitectonic region TpT, as well as of the regions which have connections with them. The posterior horn of the left lateral ventricule is usually longer and the left occipital lobe larger. The findings are associated with the leftsided location of speech functions rather than with motor dominance. Several hypotheses have been put forward attempting to explain the mode of heredity of handedness: the hypothesis of biological left--right maturation gradient, the polygenic hypothesis, further the hypothesis suggesting that one pair of genes determines the hemisphere dominant for motor and speech functions and another pair determines whether the dominant hand will be controlled by the ipsilateral or contralateral hemisphere. The hypothesis of Annette offers a plausible explanation of the heredity of handedness. It proposes that the development of a right-handed or left-handed individual is accounted for by the presence or absence of the gene which determines the dominance of the left hemisphere for speech and facilitates the development of right-handed motor dominance.