Why don’t teens think? Here’s a clue

Perhaps there’s an explanation after all for why some teenagers are so notoriously difficult: Their minds cannot yet fully reason.

Government researchers found in a recent study that the last areas of the brain to mature in humans appear to be those responsible for reasoning, problem-solving and other sophisticated functions. This doesn’t happen until sometime between the ages of 18 and 21.

The findings come from researchers at the National Institute of Mental Health in Bethesda, Md., and UCLA, who studied the brain development of 13 healthy children and teens for eight to 10 years from ages 4 to 21. The researchers took periodic scans of their brains and used brain-mapping technology. They combined the images into a time-lapse, 3-D movie that condensed 17 years of brain growth into a few seconds of images.

Areas in the extreme front and back of the brain, governing such basic functions as smell, hearing and sight, are the first to mature. The upper-middle portion of the brain, which governs movement and touch, appears to mature next. Next come the parietal lobes, associated with language and spatial orientation -- the ability to bring together sight, touch and other perceptions to get your bearings in various surroundings. Last is the prefrontal cortex, which integrates information registered by the senses and controls reasoning and decision-making.

The new images are important because “no one had actually shown that ... simple areas would develop first and mature first, and complex areas would have to wait until simple areas mature,” said lead study author Dr. Nitin Gogtay, a psychiatrist with the National Institute of Mental Health.

The study was published online last week in the Proceedings of the National Academy of Sciences.