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Researchers at the University of Toronto have discovered that higher brain centres act as "training wheels" for the lower brain by enabling it to adapt to injury.

In a paper to be published in the October edition of the Journal of Neuroscience, scientists examined the role played by the cerebral cortex - the highest brain centre - in controlling changes commonly observed at lower levels of the nervous system.

"While it has been obvious to scientists for some time that sensory information must flow up each level of the brain, it has always been a puzzle why there is such heavy feedback from higher levels back down to the lower areas of the brain," says Dr. Jonathan Dostrovsky, lead author and professor of physiology at U of T.

Lower brain centres need input from the cerebral cortex initially to adapt to damaged sensory pathways. Once the lower brain centres have been given enough time to adapt to the damage, however, the cerebral cortex is no longer needed to maintain this new re-organized state. In this sense, Dostrovsky says, the cerebral cortex acts much like training wheels for lower brain centres such as the thalamus.

"This sheds new light on the role of the cortex on the thalamus and it could possibly lead to new ways of dealing with strokes or other neurological conditions that involve loss of sensory input," says Dr. Jayson Parker, who conducted this research as part of his PhD thesis at U of T. "These results are still preliminary, but very promising."

Dostrovsky and Parker simulated injury by removing sensory input to the thalamus from the hind limb of laboratory rats, causing the cells of the thalamus to change their properties. This is known as plasticity, a process by which cells modify their properties in response to the removal of sensory input from another part of the body.

"The cortex appears to be necessary to enable these reorganizational changes to take place," Dostrovsky says. "But once it has occurred the cortex is no longer needed for maintaining the new reorganization."

Prof. Dostrovsky's work involves both research and clinical intervention for the management of chronic pain and movement disorders in humans. He was recently named chair of the scientific program committee for the next World Congress on Pain to be held in San Diego in 2002.

This study was funded by the U.S. National Institutes of Health and the Medical Research Council of Canada.

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