How do surgeons focus intently on their patients for hours on end? Why do other people have difficulty finishing a book or listening to a lecture? Can they train themselves to improve, as they might train to run a marathon or play the violin?

Scientists hope to find answers to these questions by using a new variation on brain imaging that lets people watch detailed movies of their brains in action. If this new technology can indeed strengthen the brain areas that mediate attention, people with attention deficit hyperactivity disorder (ADHD) might have a drug-free way to improve their symptoms.

Functional magnetic resonance imagining (fMRI) measures blood flow in precise areas of the brain, giving scientists an indirect measure of the brain's activity patterns. While data collected from fMRI has traditionally taken days or weeks to analyze, newer algorithms and greater computing power have collapsed that time down to milliseconds. That means scientists -- and subjects -- can watch the brain in action.

Known as real-time fMRI, the technique has been used mostly as a scientific tool. But scientists are beginning to use real-time fMRI as a form of neural feedback to teach people to consciously control their brain activity. Preliminary studies by Stanford neuroscientist Sean Mackey and colleagues have shown that the technology can help people control chronic pain (see "Seeing Your Pain," July/August.) Now scientists are setting their sights on attention disorders such as ADHD.

When you're having a conversation with a friend in the middle of a cocktail party, your brain is assaulted with huge volumes of sensory information -- the clink of martini glasses, the nasal whine of a nearby conversation. Ideally, mechanisms in the brain filter out this extraneous information, allowing you to focus attention on your companion's voice. "We know the brain can home in on visual or auditory information," says Seung-Schik Yoo, a neuroscientist at Harvard Medical School in Boston. "But for some people, it's not that easy to do."

People with ADHD may have difficulty filtering out extraneous sounds, or may find it hard to focus on complex directions or a lengthy speech. Yoo and others want to see if fMRI feedback can help strengthen the attentional machinery in the brain.

"[Researchers] understand what parts of the brain are active when people are paying attention," says Peter Bandettini, director of the Functional MRI Core Facility at the National Institute of Mental Health in Bethesda, MD. "If you could focus on those areas, it's kind of like bootstrapping yourself to pay attention."