Among the most important structural changes in the brain during adolescence are those involving the corpus callosum, the prefrontal cortex and the amygdala. The corpus callosum, a large bundle of axons that connects the brain's right and left hemispheres, thickens in adolescence, and this thickening improves adolescents' ability to process information. Advances in the development of the prefrontal cortex, the highest level of the frontal lobes, an area involved in reasoning, decision making, and self-control, continue through emerging adult years, approximately 18 to 25 years of age. The amygdala, a part of the brain's limbic system that is the seat of emotions such as anger, matures much earlier than the prefrontal cortex. Adolescents may have difficulty controlling the emotions that come from the amygdala because the prefrontal cortex is not yet fully developed.