Differential effects of prenatal testosterone on lateralization of handedness and language

Handedness is the most noticeable functional expression of cerebral lateralization in humans. However, its developmental process and plasticity remain elusive. It has been postulated that prenatal testosterone (pT) has an effect on human lateralization development. In the present study we examined the relationship between pT and handedness and compared the outcome to previously published data on language lateralization in the same children.

pT was assessed from amniotic fluid of healthy pregnant women using radioimmunoassay. Strength and direction of handedness of the children (n = 65 [31 girls, 34 boys], mean age [years]: 6.43, range: 5.97-7.53) was assessed based on hand choice during performance of age appropriate tasks. Regression procedures and the Olkin & Siotani Z-statistic were used.

Results demonstrate that higher pT exposure was related to a decrease in strength of handedness (R² = .11, p = .01). The analysis shows that pT has quite stronger explanatory power than sex by itself, although there may be an additional effect of sex independent from pT. In a subgroup of these children we recently reported that higher levels of pT are related to increased left hemisphere dominance for language. Analyses show that pT is differentially related to handedness and language lateralization in these children (Z > 2.75, p < .003).

Results imply a differential effect of pT on language lateralization and handedness. This may be explained by differential sensitivity of different areas of the corpus callosum or hemispheres for androgens, fuelling the ongoing debate about the relationship between prenatal exposure to testosterone and lateralization of brain and behavior.