Brain maturation and its relevance to understanding criminal culpability of juveniles

The purpose of this review is to summarize current understanding of the process of maturation in human brains during the juvenile period to young adulthood. We describe the methods used in such investigations, and outline the main findings regarding the course of brain development. There is much that we do not know about brain maturation, but there is congruence of evidence indicating that brain maturation is not complete until young adulthood (approximately age 21 years). Furthermore, the main index of maturation, which is rate of myelination, points to large variability in the rate of maturation among brain regions. Generally, maturation of association cortex is not complete by late adolescence, and within this cortex the prefrontal regions are last to mature. The review concludes by discussing the behavioral implications of these findings. The role of myelination is to focus and refine the operation of neural networks regulating behavior, and the frontal lobes specifically modulate and inhibit impulses, shaping behavior within the context of the environment in relation to planned action and long-term goals. Because the brain anatomy data indicate that people are not biologically prepared to exercise mature executive control required for full criminal intent until they reach adulthood, juveniles have diminished capacity in this regard and should not be eligible for the most severe punishment available for their crime.