How environment and genes shape the adolescent brain

•Brain–behavior relationships are bidirectional.•Androgens influence axon caliber, estrogens myelination.•Social interactions may shape relevant neural circuits.

This article is part of a Special Issue “Puberty and Adolescence”.This review provides a conceptual framework for the study of factors – in our genes and environment – that shape the adolescent brain. I start by pointing out that brain phenotypes obtained with magnetic resonance imaging are complex traits reflecting the interplay of genes and the environment. In some cases, variations in the structural phenotypes observed during adolescence have their origin in the pre-natal or early post-natal periods. I then emphasize the bidirectional nature of brain–behavior relationships observed during this period of human development, where function may be more likely to influence structure rather than vice versa. In the main part of this article, I review our ongoing work on the influence of gonadal hormones on the adolescent brain. I also discuss the importance of social context and brain plasticity on shaping the relevant neural circuits.