Study Illuminates Brain's Ability To "Rewire" Itself After Strokes Or Injuries

The seemingly limited ability of the adult brain to recover from stroke or accidental injury has been a major stumbling block in treating brain disorders. However, the Vanderbilt study showed new growth in cell connections following injury.

Writing in the Nov. 6 edition of Science magazine, three Vanderbilt University researchers report that cells in the adult brain can sprout new axons, or branches, that travel relatively long distances and make contact with new targets at distant sites in the brain. The new growth was found in a region of the brain called the sensory cortex that receives information from touch.

First, the normal connections among cells in the sensory cortex were studied by injecting a harmless substance that reveals or "labels" cells and makes it possible to trace the point-to-point nature of cell connections, according to Sherre Florence, research assistant professor of psychology at Vanderbilt.

She said that cells in the sensory cortex normally have specific connections with neighboring cells. For example, cells that receive information from the hand make connections only with other cells concerned with the hand.

However, in four monkeys with hand injuries, cells had connections that spanned a much wider area of the sensory cortex, a nearly twofold increase compared to normal monkeys.

"Cells within the injured hand cortex apparently grew connections into neighboring cortical zones that were unimpaired by the injury," Florence said. "And cells outside the hand region of cortex made connections to cells in the zone deprived of sensory information because of the hand injury."

According to Florence, the way the cells behaved within the zone of expanded connections changed, suggesting that the new connections made fully effective contacts with their new targets. This could give the new connections the opportunity to change brain function.

The new growth appeared to be triggered by the injury to the hand. None of the injuries directly impacted the brain, but they all had the common effect of disrupting the amount and pattern of activity being relayed to the brain from the hand.

Florence and her colleagues think that it was the massive change in activity patterns that initiated the chain of events that led to new cell growth, not the injury itself. This suggests that it may be possible to coax more flexibility out of the adult brain, taking advantage of these natural processes, in contrast to other lines of research where chemicals were administered to facilitate cell growth.

The ultimate goal is to be able to reproduce the conditions necessary for axon growth, to help cells in the adult brain form effective new long-distance connections.

This might make it possible to reverse some of the effects of damage to the nervous system from spinal cord injury or brain disorders such as stroke.

Other researchers who worked on the project were Jon H. Kaas, Centennial Professor Psychology and Professor of Cell Biology at Vanderbilt; and H.B. Taub, a Vanderbilt graduate student in psychology.