If You're Missing a Limb, the Brain Recruits Another for the Job

A new study about how the brain organizes  body part function might upend common assumptions. PhotoAbility/Getty Images A new study about how the brain organizes  body part function might upend common assumptions. PhotoAbility/Getty Images
A new study about how the brain organizes body part function might upend common assumptions. PhotoAbility/Getty Images

Recent research published in the journal Current Biology is poised to transform how scientists understand the brain, specifically which sections control which body parts. The previous line of thought was that a certain area of the brain was in charge of hand function, but new research shows that other body parts compensating for the missing hand (like a foot, mouth or arm) just as effectively "light up" the erstwhile hand area. So, instead of that section of the brain being hand-specific, it appears to actually be function-specific.

"It's kind of mind blowing for me to think we could have been getting this wrong for so long," says study co-author Tamar Makin, a neuroscientist at University College London, United Kingdom in a press release. "The implications, if this interpretation is correct, are massive."

The scientists looked at 17 people born without a hand along with 24 people born with two hands as control. The participants were video-recorded doing five everyday tasks (such as wrapping a present) and moving various body parts while their brains were scanned using functional MRI.

"We found that the traditional hand area gets used up by a multitude of body parts in congenital one-handers," says Makin. She notes that this "hand area" takes up a large portion of the brain. "Interestingly, these body parts that get to benefit from increased representation in the freed-up brain territory are those used by the one-handers in daily life to substitute for their missing-hand function — say when having to open a bottle of water."

Although still just a working theory, the concept is illustrated by 6-year-old Zion-Li Aguila-Velez, who was was born without arms, and so has used his feet to accomplish tasks with aplomb for his entire life. Alexandria Aguila-Velez of Kennesaw, Georgia, who adopted Zion from China, recalls attempts by a surgeon to fashion Spider-Man prostheses for the young child to use. "We tried it out and he just couldn't adapt to it. It would slow him down and he would cry because he wanted to do everything with his feet," Aguila-Velez says.  

Zion primarily uses his feet to dress, bathe, eat and handle all other personal hygiene. He writes, colors, paints, plays with Legos and helps his mother cook dinner. He carries around small packages of cleansing wipes to de-germ his feet come snack or meal time. Zion also enjoys skateboarding, swims "like a little fish," according to his mom, and recently enjoyed his first season of team baseball. 

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Zion Aguila-Velez, who was born without arms, feeds his mom Alexandria a piece of fruit.
Alexandria Aguila-Velez

"He never sees [having just one hand] as a challenge. He's one step ahead of me," Aguila-Velez says. "Some things my husband and I see as a challenge, we act normal about it and let him figure it out ... He comes up with better ideas than I would have!"

Interestingly, Zion's brain is better equipped to adapt to his missing limbs than that of a person who loses a hand later in life. "The brain gets its input from the body," explains James Giordano, Ph.D., neurology and biochemistry professor at Georgetown University. "For functions that need to be done, what the brain will do is use the tools at its disposal. It literally recruits or harnesses the body parts it has available. If we don't have hands, well, if we have to grab a pen or open a door we have a foot to use. The brain is a very adaptive organ."

If the limb loss occurs later in life, says Giordano, another appendage can be trained to fill in but it's more difficult because the brain has to basically rewire its connections. Neurophysical rehabilitation, as well as higher-tech approaches, like transcranial electrical or magnetic stimulation (where small electric currents are delivered to the brain) can encourage the brain to adapt. Researcher Makin is hoping that her study could help scientists determine how the brain could control, for instance, a prosthetic arm using the brain area that would have controlled that missing arm.

"I think the study demonstrates what most of the research to date has been leaning toward. The brain does remodel itself. It also remodels the sensory and motor space," says Giordano, noting that the level of remodel depends on the extent of the injury and congenital challenge. "The study demonstrates and in many ways, confirms our understanding that the brain can be more plastic than we had imagined."