That's the conclusion of researchers who found that people who have had strokes were better able to recall words after they silenced parts of the brain that therapies stimulate.

Stroke is caused when a clot forms or a blood vessel ruptures in the brain, cutting off the blood supply and killing neurons within minutes. Although the dead cells are not replaced, people can still recover lost functions such as the ability to recall words. The prevailing explanation is that healthy regions on one side of the brain learn to take over the jobs that were done by the corresponding cells that died in the other hemisphere. This idea is supported by studies using functional magnetic resonance imaging that have revealed increased electrical activity in regions in the intact hemisphere compared with the same area in healthy brains.

Many therapies are designed to boost this reorganisation by stimulating the intact hemisphere. For instance, speech-impaired patients are often encouraged to sing a song containing the word they are seeking. The hope is that embedding it in a heavily prosodic, or tonal, context will engage the right hemisphere-which processes prosody -and bypass the damaged left hemisphere that normally processes speech. In this way, stroke patients learn to recall a stored word by a different route.

Yet despite therapy, many patients fail to recover some lost functions. This suggests that overstimulating the healthy regions of the brain may be stifling recovery rather than aiding it, says Alvaro Pascual-Leone, director of the Laboratory for Magnetic Brain Stimulation at Harvard Medical School in Boston.

His team tested the theory by using magnetic fields to suppress those areas instead. Using a technique called transcranial magnetic stimulation, the researc
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Contact: Claire Bowles
claire.bowles@rbi.co.uk
44-207-331-2751
New Scientist
19-Jun-2002