Adolescence, an important window of opportunity and vulnerability for brain development Although less well studied, adolescence is also a critical period of brain development. The brain undergoes important organizational changes, with the re-emergence of gonadotropin-releasing hormone triggering a cascade of hormone dependent processes. Other biological processes involve epigenetic factors, which are highly sensitive to the environment and may therefore make this period of growth more vulnerable to external insults (Morrison, 2013). Moreover, the prefrontal cortex, which carries out important functions such as internally guided behaviors (control of emotion), logical thinking, working memory and organizing skills (executive function), is the last region of the brain to mature (early-twenties). The synaptic plasticity of the prefrontal cortex is accentuated during adolescence, a process that involves loss of grey matter density, and an increase in white matter volume, cerebral blood flow and synaptic pruning. Adolescence is also a time of refinement of brain connectivity and complex behaviors (Selemon, 2013). It is widely recognized that the synaptic plasticity of the brain decreases with age (Morrison, 2013; Selemon, 2013), but this pattern does not seem to follow a linear trend, and adolescence is an important period during which brain development can be enhanced and protected from environmental hazards with long-term consequences (everything from air pollution to social stress). There is a need for greater understanding of the biological pathways through which the environment affects human brain development, particularly during adolescence, when the most complex behaviors are refined to adulthood sophistication.