A recent article by Dr Michael Lombardo and colleagues, published in Biological Psychiatry, investigates the mechanistic effects of prenatal testosterone on approach-avoidance behavioural tendencies. Approach-avoidance behaviours are present in many neuropsychiatric conditions with skewed sex ratios. Because prenatal testosterone levels are much higher in boys than in girls, these levels may affect brain regions involved in approach-avoidance behaviours (i.e. reward- or punishment-seeking behaviours) that show discrepancy between the sexes.

This research is part of a longitudinal project looking at the effects of prenatal influences, including prenatal testosterone levels, on behavioural and brain development. Using fMRI the authors scanned brains of boys between 8-11 years old while they viewed happy, fear or neutral faces in the scanner.

It was found that areas in the reward system, such as the caudate, putamen and nucleus accumbens, were all positively correlated with prenatal testosterone levels when looking at a happy face compared to looking at a fear expression. A statistical mediation analysis also showed that increasing prenatal testosterone levels predicts increased responsiveness of the caudate, putamen and nucleus accumbens to positive cues than to negative cues.

Testosterone is therefore suggested to act as a foetal programming mechanism on the neural reward system and also influence behavioural approach tendencies later in life. These results may be important for studies investigating neuropsychiatric conditions with skewed sex ratios, and those that affect the reward system, approach behaviour and emotion processing.