Brain Reprograms Itself After Stroke.

• Position: Brief Article

Functional imaging of the brain demonstrates that this highly complex organ adapts to injury by redistributing its cognitive workload across established neural networks and recruiting local cortical areas to fill in for lost functions like speech and language comprehension. "Functional MRI [magnetic resonance imaging] indicates that the dogma that some areas of the brain ... are not important for normal function is clearly fallacious," argues Keith Thulborn, director of MR research at the University of Illinois at Chicago. "Loss of any brain tissue is likely to compromise the reserve capacity of many large-scale neurocognitive networks that will ultimately be reflected in the performance of more difficult tasks or recovery from subsequent disease processes."

Watching the brain at work with a very-high-field MRI scanner, Thulborn has mapped a two-stage recovery process in patients who lost their language skills after strokes. In one patient suffering from damage to Wernicke's area (the region in the left cortex that controls the understanding of language), functional MRI showed that the brain initially recouped by allocating speech comprehension to an area on the opposite side of the brain.

Over time, while Wernicke's area remained damaged, an adjacent area took on this cognitive task. The ability of the brain to maintain performance by recruiting undamaged portions of the cortex may suggest why functional recovery can occur even following large strokes.

One key factor in recovery time, Thulborn suggests, is whether white matter has been damaged. White matter consists of myelinated neuronal axons that serve as cables linking the different areas of the cortex. When these are injured, vital connections needed to allocate functions elsewhere are lost. "The involvement of white matter tracts portends slower and reduced recovery. This may reflect reduced capacity to redistribute workload when the connectivity through white matter is disrupted."

The...