Organisational and Activational Effects of Prenatal Exposure to Testosterone on Lateralisation in the Domestic Chicken (Gallus gallus domesticus)
Brain lateralisation is the specialisation of the two hemispheres on different tasks and is supposedly beneficial for individuals. There is a long-standing debate about to what extent and via which pathways prenatal exposure to testosterone affects lateralisation. Birds are excellent models to investigate this since the embryo can be manipulated outside the mother’s body. Moreover, avian eggs contain substantial concentrations of maternally derived hormones known to affect a wide array of behaviours. Therefore, birds provide an excellent model to integrate two flourishing fields: that of hormone mediated maternal effects and of lateralisation. In addition, in most birds the eyes are placed laterally and the information exchange between the two hemispheres is limited, facilitating measuring lateralisation of visually guided behaviour. We will discuss results of egg injection experiments on short- and long-term effects on the lateralisation of visually guided behaviours in the domestic chicken. Lateralisation in young birds, young chicken in particular, has been extensively studied, but to what extent lateralisation is consistent over life and affected by prenatal exposure in adult birds remains elusive. Our results do not show an effect of the prenatal manipulation, in contrast to some other studies, perhaps because ours were carefully carried out within the physiological range of the species. They therefore do not lend support for either of the three main hypotheses about how prenatal testosterone affects the development of lateralisation in the ‘Geschwind-Behan–Galaburda’ hypothesis, the ‘Corpus Callosum’ hypothesis and the ‘sexual differentiation’ hypothesis. Correlations between testosterone levels and lateralisation both measured in adulthood suggest a role for activating effects of this hormone on lateralisation, at least in males. Correlations of lateralisation indices at young and adult age within individuals were also inconsistent, suggesting brain reorganisation during late development and challenging functional explanations of lateralisation for adult chickens.
KeywordsCorpus Callosum Sexual Differentiation Prenatal Exposure Adult Bird Tonic Immobility
The Geschwind-Behan–Galaburda hypothesis
We thank Mirte Greve, Sjoerd Veenstra, Roelie Veenstra-Wiegman, Bonnie de Vries, Ilse Weites, Martine Muller and Saskia Helder for their assistance during several phases of the current study. This experiment was conducted under licence number 4765A of the animal experimentation committee (DEC) from the University of Groningen. BR was funded by NWO-grant 051-14-016, KP by EU grant EDCBNL.
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