Immobilization of one hand causes rearrangement of brain matter

What happens in the brain of right-handed people if their dominant hand is immobile for two weeks? This is the question addressed in the latest study led by Professor Lutz J-ncke and the Trauma Surgery Department at Zurich University Hospital. For the study, ten right-handed people with broken upper right arms were examined. Because of the plaster or sling, the test people's right hands were restricted to little or no movement for fourteen days. Therefore they used their left hands for daily activities such as eating, brushing their teeth or writing. The participants were given two MRI brain scans: one 48 hours after injury and a second 16 days after the arm was immobilized. Based on the scans, the neuropsychologists analyzed the test people's gray and white brain matter. They calculated the thickness of the cerebral cortex and the values of the corticospinal tract and measured the fine motor skills of the left, free-moving hand.

"In a short space of time, the immobilization of the right hand changed the sensory and motor brain areas," explains the author of the study, Nicki Langer. The gray and white brain matter of the motor areas in the right brain hemisphere that control the immobilized right hand decreases while the brain matter of the right motor areas that control the inferior left hand grows. "It is interesting that the fine motor skills of the left hand improved considerably during the 16 days the right hand was restricted," adds neuropsychologist Lutz J-ncke. The improvement in motor performance correlates with the anatomical change: the better the fine motor skills of the left hand, the more brain substance there is in the right motor area. And: the better the fine motor skills of the left hand, the less brain matter there is in the left motor area.

The results of the study are interesting for the treatment of strokes. In a therapeutic approach, for instance, the undamaged arm can be immobilized to strengthen the affected arm and stimulate the corresponding brain area for new skills. "Our study shows that this kind of therapy has both positive and negative effects," says Langer. "Our study also supports the current trauma surgery guidelines, which state that an injured arm or leg should only be immobilized for as short a period as possible, but as long as necessary," concludes Langer.