Brains of one-handed people suggest new organization theory

April 20, 2017, Cell Press
Credit: Wikimedia Commons

In people born with one hand, the brain region that would normally light up with that missing hand's activity lights up instead with the activity of other body parts—including the arm, foot, and mouth—that fill in for the hand's lost function. Now, researchers reporting in Current Biology on April 20 say that the discovery could shake up scientists' fundamental understanding of how the brain is organized.

"Scientifically, I think one way to put our results in context is to say, what if the hand area is not the hand area per se, but just the part of the brain in charge of 'normally' carried by that hand?" says Tamar Makin of University College London, United Kingdom.

"In intact participants, all this is carried by the non-dominant hand," she continues. "But the fact that we see such a striking different representation in that area in congenital one-handers might suggest that this is not actually the hand area. If true, this means we've been misinterpreting based on part, rather than based on function. It's kind of mind blowing for me to think we could have been getting this wrong for so long. The implications, if this interpretation is correct, are massive."

But, she cautions, it's still just a working theory at this point.

Scientists have long known that different parts of the brain control different body parts. In the new study, Makin and her colleagues, including Avital Hahamy at Israel's Weizmann Institute of Science, set out to explore what happens to brain organization in people for whom a body part never existed.

This video shows one-handed people who participated in the study doing everyday tasks. Credit: Hahamy et al.

The researchers studied 17 people who lacked a hand from birth along with 24 matched, two-handed controls. Each participant was video recorded while completing five everyday tasks, such as wrapping a present or handling money, to see how he or she went about it. Participants were also asked to move various parts of their bodies while their brains were scanned using functional MRI (fMRI).

"We found that the traditional hand area"—which, Makin notes, takes up a rather sizable portion of the brain—"gets used up by a multitude of body parts in congenital one-handers. 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."

Whether Makin's theory on brain organization corresponding to function instead of body parts pans out or not, the findings reveal remarkable brain plasticity. Her hope is to find a way to encourage the brain to represent and control artificial , such as a prosthetic arm, using the area that would have controlled the missing .

"If we, as neuroscientists, could harness this process, we could provide a really powerful tool to better healthcare and society," Makin says. "Unfortunately, this process is currently quite restricted in the brains of adults. But by learning how this occurs spontaneously in one-handers, we can get a handle on what we might be able to achieve."

Explore further: 'Unfussy' brain finds ways of coping with loss of a hand

More information: Current Biology, Hahamy et al.: "Representation of multiple body parts in the missing-hand territory of congenital one-handers" http://www.cell.com/current-biology/fulltext/S0960-9822(17)30352-4 , DOI: 10.1016/j.cub.2017.03.053

Related Stories

'Unfussy' brain finds ways of coping with loss of a hand

January 8, 2015
People born without one hand, who are still able to use both limbs well in otherwise two-handed tasks, are likely to show brain activity which resembles that of people with two hands, an Oxford University study has found.

Amputees' brains remember missing hands even years later

August 30, 2016
Our brains have a detailed picture of our hands and fingers, and that persists even decades after an amputation, Oxford University researchers have found. The finding could have implications for the control of next generation ...

Getting a handle on brain organization: Study finds even those born without hands show hand-tool overlap

April 17, 2017
Tool use has long been considered one of the behaviors that makes humans, well, human.

Researchers examine unusual condition of mirror-touch synesthesia

February 6, 2017
When a student in a University of Delaware study watched a video of someone else's hand being touched, she felt the touch on her own hand. While that may seem a little eerie to most of us, she's not alone. About two in 100 ...

A dominant hemisphere for handedness and language?

July 4, 2014
Through an innovative approach using a large psychometric and brain imaging database, researchers in the Groupe d'Imagerie Neurofonctionnelle (CNRS/CEA/Université de Bordeaux) have demonstrated that the location of language ...

Study finds emotion reversed in left-handers' brains

May 2, 2012
The way we use our hands may determine how emotions are organized in our brains, according to a recent study published in PLoS ONE by psychologists Geoffrey Brookshire and Daniel Casasanto of The New School for Social Research ...

Recommended for you

New technique helps uncover changes in ALS neurons

June 22, 2018
Northwestern Medicine scientists have discovered that some neurons affected by amyotrophic lateral sclerosis (ALS) display hypo-excitability, using a new method to measure electrical activity in cells, according to a study ...

Broken shuttle may interfere with learning in major brain disorders

June 22, 2018
Unable to carry signals based on sights and sounds to the genes that record memories, a broken shuttle protein may hinder learning in patients with intellectual disability, schizophrenia, and autism.

Watching stem cells repair spinal cord in real time

June 22, 2018
Monash University researchers have restored movement and regenerated nerves using stem cells in zebra fish where the spinal cord is severely damaged.

Scientists discover fundamental rule of brain plasticity

June 21, 2018
Our brains are famously flexible, or "plastic," because neurons can do new things by forging new or stronger connections with other neurons. But if some connections strengthen, neuroscientists have reasoned, neurons must ...

Waking up is hard to do: Prefrontal cortex implicated in consciousness

June 21, 2018
Philosophers have pondered the nature of consciousness for thousands of years. In the 21st century, the debate over how the brain gives rise to our everyday experience continues to puzzle scientists. To help, researchers ...

Researchers find mechanism behind choosing alcohol over healthy rewards

June 21, 2018
A new study links molecular changes in the brain to behaviours that are central in addiction, such as choosing a drug over alternative rewards. The researchers have developed a method in which rats learn to get an alcohol ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.