Plasticity and function of cerebral lateralization

PhD ceremony: Ms. J.M. Lust, 13.15 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: Plasticity and function of cerebral lateralization

Promotor(s): prof. J.M. Bouma, prof. A.G.G. Groothuis

Faculty: Behavioural and Social Sciences

Lateralization refers to the division of labour between the hemispheres. The studies presented in this thesis addressed the developmental plasticity and function of cerebral lateralization. The access to an unique dataset of prenatal testosterone (pT) levels and the use of fTCD to measure individual lateralization patterns enabled us to test longstanding hypotheses.

Higher pT values were related to stronger lateralization of language to the left hemisphere. Moreover, the results suggested that different mechanisms may underlie this effect in girls and boys. The results suggest that in girls higher prenatal testosterone exposure facilitates left hemisphere language processing, whereas in boys it reduces the information transfer via the corpus callosum.

Higher pT levels were also related to decreased strength of lateralization. PT was thus differentially related to handedness and language lateralization.As motor brain areas and language brain areas are connected by different parts of the corpus callosum, a differential effect of pT on handedness and language lateralization may be explained by a differential effect of pT on different callosal areas.

Since research in animals has shown that lateralization is a wide spread phenomenon and has endured evolution and because deviant lateralization has been related to disorders in humans (e.g. dyslexia) is has been hypothesized that lateralization is advantageous to the individual. However, the present studies do not show an advantage of either stronger nor typical lateralization on task performance.