The human brain is not fully developed by the time a person reaches puberty. Between the ages of 10 and 25, the brain undergoes changes that have important implications for behavior. The brain reaches 90% of its adult size by the time a person is six or seven years of age. Thus, the brain does not grow in size much during adolescence. However, the creases in the brain continue to become more complex until the late teens. The biggest changes in the folds of the brain during this time occur in the parts of the cortex that process cognitive and emotional information. Changes to the brain directly influence changes to behavior and mental process. We will discuss some of these issues.

Figure 5.1.1. The brain reaches its largest size in the early teen years but continues to mature well into the 20s.