FOR DECADES, neuroscientists were like mental drill sergeants, always directing volunteers to do some-thing: read this word, listen for that sound, add these numbers, tap your finger, and so forth.
As volunteers worked, scanners tracked changes in their brain’s blood flow and oxygen use, which increase when neurons in a brain region become more active. Researchers could compare and contrast the results of slightly different tasks (reading a word aloud versus reading a word silently, for example) to determine which brain regions were essential to particular mental abilities (in this example, speech).
Scientists built a tremendous wealth of knowledge using such approaches, but Marcus E. Raichle, MD, professor of radiology, neurology and neurobiology, and his colleagues had lingering questions.
The condition typically results from an injury to the right side of the brain. That a right-side injury disables left-side attention is not surprising; neurologists’ established understanding of the brain puts the brain’s right side in charge of the body’s left side, and vice-versa.
But when scientists used conventional brain-scanning techniques to study spatial neglect patients as they performed visual tasks, they could see that not only had activity in the right side of the brain diminished, the left side of the brain had become significantly busier. Greater overactivation of the left side was linked to greater problems with spatial attention.
In more recent studies, the researchers tested whether FC could be used to predict how stroke damage affects patients. In 23 patients who had recently suffered a stroke on one side of the brain, researchers assessed the strength of the connections in two networks, one for moving the arm and one for paying attention to the environment. Each includes regions in both hemispheres of the brain. Patients with damage to connections linking regions in both hemispheres were more likely to suffer a greater degree of impairment after the stroke.
That meant, for example, that stroke damage on the left side of the brain might lead to problems with control of the right arm, but the losses were worse if the left-side damage disrupted network connections with the right side of the brain.
This and other recent findings have neuroscientists thinking they may need to adjust their picture of how the brain’s hemispheres divide control of the body.
“It’s not wrong to say that one side of your brain controls the opposite side of your body, but we’re starting to realize that it oversimplifies things,” says Alex Carter, MD, PhD, assistant professor of neurology.
To further define and confirm FC’s clinical applicability, researchers are planning additional studies of brain injury patients. They also plan to use FC in long-term studies of the recuperation of such patients.
This story appeared in the Spring 2010 Outlook magazine.