Add to ORKGBrain lateralization is the phenomenon that both hemispheres of the brain are specialised in different functions. Lateralization differs in strength and direction between individuals and among tasks within individuals, potentially affecting cognitive performance. There is debate to what extent individual differences in lateralization are due to early or later exposure to sex hormones. We use unique data sets to test this: (1) Existing data on prenatal hormone exposure, obtained from amniotic fluid during pregnancy of the mothers, will be correlated with brain lateralization and cognitive performance in a group of healthy adolescents of 13-15 years old (30 boys, 30 girls). (2) Current testosterone and progesterone levels are measured in sali...