Editor's note: The orignal online version of this story was previously posted.

We often hear that teens are irresponsible because their brains are immature. But, contradicting that idea, teen turmoil is completely absent in more than 100 cultures around the world [see “The Myth of the Teen Brain,” by Robert Epstein; Scientific American Mind, April/May 2007]. Nevertheless, neuroscience studies do indeed suggest that the gray matter in the frontal cortex of teens, as compared with adults, is not fully developed.

Now a study by neuroscientist Gregory S. Berns and his colleagues at Emory University adds a new wrinkle to the gray matter findings, reporting that teens who are risk takers and drug users actually appear to have a more developed brain than their conservative peers.

The Berns team assessed the risk-taking tendencies of 91 teens between the ages of 12 and 18 with a written test and a drug test. Then, using a relatively new MRI technology called diffusion tensor imaging, the researchers looked at the amount of white matter in the frontal cortex of the teens’ brains. White matter contains the protein myelin, which coats neurons’ spindly axons as they reach toward other areas of the brain. Myelin is important for efficient signaling between neurons, and it is known to grow considerably between childhood and adulthood.

The investigators found that engaging in dangerous behaviors was associated with increased white matter, a result directly opposite to the gray matter findings. One possible interpretation: people whose brains mature early might be more prone to engage in adult activities. But Berns suggests that the entire teen brain idea might be overhyped. “Nobody denies that the brain develops or that teens take risks,” he says, “but how the two observations got intertwined is beyond me.”

Developmental psychologist Laurence Steinberg of Temple University questions the significance of the new study. Other researchers have found a connection between increased white matter and reduced impulsivity, Steinberg explains, which could mean a reduced likelihood of risk taking—the opposite of the Berns finding. Renowned neuroscientist Michael S. Gazzaniga of the University of California, Santa Barbara, is more impressed. “So much for the much touted model of the teenage brain,” Gazzaniga says. “Back to the drawing boards again.”