A growing body of research into adolescent brain development indicates that the brains of even those over the age of 18 continue to physically change in ways related to culpability for criminal offenses. The Supreme Court referred to such scientific evidence regarding those under the age of 18 when it struck down the death penalty for juveniles in 2005 (Roper v. Simmons) and when it recently limited life without parole sentences for juveniles. According to Laurence Steinberg (pictured), a professor of psychology at Temple University, the brain continues a process called myelination into a person’s twenties. That process affects planning ahead, weighing risks and rewards, and making complex decisions. This research may yield mitigating evidence for younger defendants, including accused Boston marathon bomber Dzhokhar Tsarnaev. Steinberg’s research shows that someone like Tsarnaev, who was 19 at the time of the bombing, may not have the same understanding of his actions as an older adult would. Young adults are particularly susceptible to the influence of peers. “What we know is that this is an age when people are hypersensitive to what other people think of them. It’s also an age when people are trying to figure out who they are, and one way is by identifying with a group. There probably are similarities between the dynamics here and dynamics of antisocial or delinquent gangs. Older, more powerful young adults persuading younger adolescents to do their bidding for them,” Steinberg said.

(D. Goldstein, “The Teenage Brain of the Boston Bomber,” The Marshall Project, January 8, 2015). See Juveniles and Studies.

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