Rewiring damaged brains

Recent research will, scientists hope, improve the human brain's ability to repair or reorganise itself after injury or disease, in infancy and eventually in adulthood.

Fish are much better at this than humans. If the brain of a fish is seriously damaged, it repairs itself within a month. An average fish can produce 100,000 brain cells every two hours to replace those lost through injury.

Scientists at Manchester University, England, believe that substances that stimulate this remarkable growth in the brains of fish may be able to do something similar in the human brain. They are carrying out research to test the idea.

Another group of researchers, at the Royal Victoria Hospital in Newcastle, north-east England, is investigating the infant human brain's capacity to rewire itself in some children who are born with cerebral palsy or those who suffer a stroke in early infancy. The researchers hope to learn how to encourage this rewiring in other children in whom it does not happen naturally and perhaps, ultimately, in adults.

Over the last 10 years Dr Gunther Zupanc, of the Department of Biological Sciences in the University of Manchester, has shown that, unlike human brains, the brains of fish produce new cells all the time. If an injury occurs, the damaged brain cells undergo apoptosis, a controlled process of cellular suicide whereby the damaged cells are broken down, packaged and neatly disposed of without damaging neighbouring cells or causing inflammation.

Meanwhile, new brain cells are produced from a pool of continually replenished young, undifferentiated stem cells that then differentiate to form whatever kinds of brain cells need replacing after injury. Research has revealed that the human brain repairs itself much less effectively than that. Damaged human brain cells are not neatly disposed of but spill out their contents causing inflammatory reactions in neighbouring tissues that in turn cause a second wave of unnecessary cell death.

Using magnetic brain-scanning techniques the Newcastle team has shown that, in some children with cerebral palsy, the brain has partially compensated for damage by using the right hemisphere (half) of the brain to take over functions which would normally be performed by the left hemisphere.

The brain scanning has revealed that in some infants affected by cerebral palsy the right side of the brain takes over functions normally performed by the left side. By understanding how this reorganisation occurs, researchers hope to find ways to stimulate it to happen in children affected by strokes or cerebral palsy in whom brain reorganisation has not happened naturally or has been less effective.