Inside The Teenage Brain

Over the past 25 years, neuroscientists have discovered a great deal about the architecture and function of the brain. Their discoveries have led to huge strides in medicine, from pinpointing the timing at which children should be operated on for vision problems to shedding light on the mechanisms that cause such diseases as schizophrenia. Much of the early focus of the research was on the early years of development or on diseased brains. Now, with the advent of new imaging techniques, researchers are able to examine normal brains and brains of people throughout their lives.

Before the advent of magnetic resonance imaging (MRI), scientists already knew a lot about how the brain functioned. When people suffered brain damage or injury to particular parts of the brain, scientists could see what functions were impaired, and infer that the injured areas governed those functions. For example, people who had strokes in the area of the brain affecting speech lost the ability to speak. Autopsies showed when particular parts of the brain matured, the connections were wrapped in white matter, or myelin.

With functional MRIs, researchers can see how the brain actually functions -- what parts of the brain use energy when performing certain tasks. They know, for instance, the particular part of the brain that "lights up" when performing a visual task. Those images in which brain activity is measured are called "functional" because they measure how the brain performs tasks rather than simply mapping out the structure of the brain.

FRONTLINE's "Inside the Teenage Brain" focuses on work done by Dr. Jay Giedd at the National Institute of Mental Health in Bethesda, Md., together with colleagues at McGill University in Montreal. In a particularly interesting study, Dr. Giedd looked at the brains of 145 normal children by scanning them at two-year intervals. This was work Giedd was only able to do with magnetic resonance imaging, because it requires neither harmful dyes nor radiation, making the study of normal children, as opposed to sick ones, ethically tenable.

What the researchers have found has shed light on how the brain grows and when it grows. It was thought at one time that the foundation of the brain's architecture was laid down by the time a child is five or six. Indeed, 95 percent of the structure of the brain has been formed by then. But these researchers have discovered changes in the structure of the brain that appear relatively late in child development.