Four specific structural changes in the brain during adolescence are noteworthy. First, there is a decrease in gray matter in prefrontal regions of the brain, reflective of synaptic pruning, the process through which unused connections between neurons are eliminated. This occurs mainly during pre-adolescence and early adolescence, the period during which major improvement in basic cognitive abilities and logical reasoning occur. Second, important changes in activity that involve the neurotransmitter dopamine occur during early adolescence, especially during puberty. Because dopamine plays a critical role in how humans experience pleasure, these changes have important implications for sensation-seeking. Third, there is an increase in white matter in the prefrontal cortex during adolescence. More efficient neural connections within the prefrontal cortex are important for higher order cognitive functions. Fourth, there is an increase in the strength of connections between the prefrontal cortex and the limbic system, which is especially important for regulating emotion. In the course of these changes in brain structure and functions, there is no simple answer as to when an adolescent brain becomes an adult brain. The consensus that emerges from recent research on the adolescent brain is that teens are not as mature in either brain structure or function as adults, such that adolescence is a developmental stage when individuals are, on average, not as mature as they will be when they become adults. The most significant challenge for those who wish to incorporate the findings of neuroscience in policy will be a multidisciplinary appreciation of the complicated interplay of biological maturation and environmental influence as they jointly shape adolescent behavior. 10 listings for recommended reading