Although right-handed people may feel helpless with their right arm in a plaster, the brain acts quickly to compensate for the loss by adapting anatomically and increasing its activity on the opposite side of the body.
“Results show that the brain adapts rapidly to changing demands,” researcher Nicki Langer told The Local.
Researchers at the Trauma Surgery Department of Zurich University Hospital have demonstrated that the brain exhibits significant anatomical changes in particular areas when patients only used their left hand in the 16 days after the injury.
Left brain areas lose some of their thickness, while areas on the right-hand side compensate by growing in size. The fine motor skills of the otherwise lesser-used left hand also improve considerably.
For the study, led by professor Lutz Jäncke, ten right-handed people with broken upper right arms were examined shortly after their injury. With their arms in a plaster or sling, the patients' right hands were restricted to little or no movement for 14 days. As a result, they used their left hands for daily activities such as eating, brushing their teeth or writing.
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 subjects' grey 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 period of time, the immobilization of the right hand changed the sensory and motor brain areas,” explained Langer.
The grey and white brain matter of the motor areas in the right brain hemisphere decreased while the brain matter grew for the right motor areas that control the inferior left hand.
Given the results, Langer said that “an injured extremity should be immobilized for as long as necessary but as short as possible”, because “immobilization has negative effects for the brain as well, since it decreases the activity and size of the brain that controls the injured arm.”
The research team did not follow patients after the plaster was removed, but Langer said he assumed that “changes in the brain only stay for as long as the arm is immobilized and for a short period afterwards.”
The researchers believe the results of the study are significant for the treatment of strokes in which the immobilization of an arm or leg on the side of the body not affected is key to the recovery of the affected side.
Langer said the fact that the brain changes so rapidly should make doctors consider “motivational instructions” rather than immobilization for stroke patients in order to prevent further damage of the brain.
The study marks the first time ever that researchers have carried out a “longitudinal study” on patients with immobilized extremities.
This means the brain was studied right after the injury. Scientists then had “some sort of pre-injury data”, since there was very little time for the brain to change, and were also able to gather data at the point when the immobilization concluded. Previous studies had only measured brain activity after a limb had been amputated.