Another way to study ADHD is by taking “pictures” of the brain. Using a technique called functional magnetic resonance imaging, or fMRI, scientists can determine which parts of the brain are “activated” when performing a task that measures attention or learning.
The MRI scanner consists of a large, doughnut-shaped magnet that can generate magnetic fields several thousand times stronger than the Earth’s field. Functional MRI measures changes in the magnetic properties of blood as it transports oxygen to brain tissue in response to increased neuronal activity.
“Neuronal activation requires energy,” says John Gore, Ph.D., director of the Institute of Imaging Science at Vanderbilt University Medical Center. “To get the energy, the blood flow increases, bringing oxygen and glucose. The net effect is you wash out deoxygenated hemoglobin (hemoglobin that has given up its oxygen) from tissue, and the MRI signal increases.”
After climbing into the magnet and staying very still, the subject is asked to look at a picture, or listen to sounds, or perform a physical function, such as tapping his or her finger during the study. The signal can then be used to pinpoint the area of the brain involved in the cognitive function. Because it is non-invasive and does not involve the use of radiation, fMRI is a preferred technique for scanning the brains of children.
Before he moved last year to Vanderbilt, Gore helped pioneer the application of fMRI to reading disabilities at Yale University. He and his colleagues, who included Dr. Sally Shaywitz, reported this summer that the neural circuitry for reading is present in even the most persistently poor readers, but it has not been properly activated. The study supports the value of early interventions aimed at stimulating the ability to sound out words and understand word meanings.
Gore, who is Chancellor’s University Professor of Radiology & Radiological Sciences and of Biomedical Engineering, is continuing to push the frontiers of fMRI. He and his colleagues at the Vanderbilt Kennedy Center for Research on Human Development are studying brain activation in children who have trouble with math, and they’re planning to study children with ADHD who were exposed to cocaine in the womb, to see if they respond differently to methylphenidate.
“The main issue at the moment is to even know which circuits are involved because different drugs do target different parts of the brain,” Gore says. “Until we had imaging, there was no way to know about the circuits in the brain, other than if somebody actually had lost or had damage to a particular part of the brain (through a stroke, for example).”
Today, with techniques such as fMRI, “we’ve shown that you can detect the effects of different types of interventions,” he says. “You can now begin to use this as a tool to actually monitor treatments.”
There are limitations: Some children feel claustrophobic in the “doughnut,” or can’t stay still for very long. The technique also is not very good at determining which part of the brain activates before another.
The technique also is expensive—currently running about $500 to $800 for an hour-long exam, Gore says. But if it can help identify problems with brain function and achieve better outcomes, fMRI would save money in the long run, he says.