The Washington Post

Brain quickly adapts when arm is immobilized, study finds

When I had my first baby, I was amazed to see how quickly I, a right-handed person, learned to accomplish certain tasks with my left hand while holding my daughter in my right arm. “Look at me, brushing my teeth like a born lefty!” I remember thinking on my first morning as a new mom.

I don’t know whether that newfound skill at using my unaccustomed hand caused any physical change to my brain. In fact, I hadn’t thought about that experience for years, until I read a study published Monday afternoon in the journal Neurology.

That research looked at 10 right-handed people (a tiny sample, the authors admit) whose right-arm injuries required them to wear a cast or sling for at least two weeks. Each subject underwent motor-skills testing of their left hand and a brain MRI within 48 hours of injury and again 16 days after being placed in the cast or sling. During that period, the right hand and arm were completely immobilized, unable even to wield a toothbrush or spoon, for instance.

The researchers observed decreases in the thickness of brain tissue in the left side of the brain — responsible for controlling the right side of the body — and increases in the thickness of tissue in the right side of the brain. Those changes corresponded to increased motor skills in the left hand.

In short, the study showed the brain adapting quickly to the loss of use of the right hand and arm, shifting capacity from the side of the brain linked to the disabled limb to the side associated with the unencumbered limb. The authors speculate that the brain’s accommodation prepared the left hand to do the compensatory work, though they allowed for the possibility that the process worked the other way around, with the increased use of the left hand increasing capacity in the right side of the brain, even as the decreased use of the right hand decreased capacity in the left side.

The authors note that their work could lead to improved therapies for stroke victims and others who have lost use of a limb, though they point out that larger studies — and research to determine whether those brain changes are long-lasting — are in order to build on their findings.


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