A unique study imaging brain activity in children born with upper limb difference – for example, one hand – has shown the amazing ability of the brain to adapt to compensate and support their daily lives.
The research, led by a team at the University of Cambridge and Durham University, reveals widespread changes in the brain as it devotes more resources to help the children adapt to the world around them.
Our brains hold a map of the body in an area known as the somatosensory cortex, with different regions corresponding to different body parts. These maps are responsible for processing sensory information, such as touch, temperature and pain, as well as body position.
The extent to which these maps are adaptable or set in stone is not clear. Although the brain is widely believed to be plastic in early life, able to reorganise itself to compensate for blindness or limb differences, the evidence comes almost exclusively from studies with adults. This makes it impossible to tell retrospectively how, when and why any reorganisation took place – is it due to changes in behaviour during childhood, for example, or is something else driving this reorganisation?
One of the reasons for this knowledge gap is the challenge of doing brain imaging studies in children, who tend to move around much more than adults, making it hard to map brain activity using functional magnetic resonance imaging (fMRI), which allows us to see the human brain in sufficient detail to answer such questions.
Studying differences in brain activity
The Cambridge and Durham team developed a test that could overcome this challenge, allowing them to study brain activity among 16 children aged between five and seven years old with a congenital limb difference, and 21 children of the same age who had no limb difference. One in 2,000 newborns in the UK is born with an upper limb difference – in some cases, this means having one hand, with the arm ending below the elbow. The researchers also recruited two adult groups – one who had been born with a similar limb difference, and one without.
The results of the study are published today in Nature Communications.
In the first part of the study, the participants were asked to perform a number of everyday tasks, such as opening a jar or unwrapping a sweet, to allow the researchers to see how they compensated for their limb differences during daily activities.
Next, the children spent time in an fMRI scanner. Conscious that a scanner may be daunting or even frightening to a young child, the team took time to familiarise them with the machine.
In the task, participants were told a story about an enchanted forest where butterflies had become invisible. Participants were asked to help make the butterflies visible again by wearing special devices attached at several places on the body – the chin, arm, torso, leg, foot, thumb and forehead. These devices, developed at EPFL, Switzerland, fluttered on the skin to mimic the sensation of butterfly wings. The researchers could then see which areas of the brain map activated in response to this stimulation of different body parts.
How the brain adapts to upper limb difference
A recent study showed that when an individual loses a hand during adult life, the brain map representing this limb persists . This new study, however, showed that for children born with one hand, the brain area that would typically be allocated to the 'missing' limb instead represented multiple parts of the body.
But this was not all. The researchers also observed that changes to the body maps were not confined to the hand area. Instead, the entire body map from the toes to the forehead changes, shifting towards the brain map of the hand.
Professor Tamar Makin from the MRC Cognition & Brain Sciences Unit, University of Cambridge, said: "These kids have to figure out how to adapt to a world that's been designed for people with two hands, and they come up with unique and interesting behaviours, using lots of different body parts. This raises a really interesting question about how their brains adapt to support this unusual journey.
"Surprisingly, the brain seems to be already set up for this journey. Very early on we see more brain resources devoted to other body parts, that they're using territory designed by evolution to support hand function. Their entire body map is shifted and changed from an early age. On top of that, in each child's brain we see bespoke tailoring at a smaller scale based on the strategies that they've evolved."
The team worked with the charity Reach, which supports families and young people with upper limb difference, and was instrumental in helping recruit families to take part in the study.
Professor Dorothy Cowie from the Department of Psychology, Durham University, said: "A lot of the parents we meet have had very little information about their child's limb difference and how it will impact their daily life, let alone what's happening in the brain.
"Our research shows how adaptable the human brain is, and we hope this is reassuring. Their child's brain is wired differently to their two-handed peers so that it can support their different approaches to doing things, such as using their legs or torso to help open a jar. Their child will figure things out in their own way, and their brains will support these developing behaviours."
The team ran a computational model to try and understand how these widespread changes occur. Traditional thinking suggests a 'use it or lose it' strategy – the more you use a limb, the stronger its representation becomes; if you no longer use a limb, activity in that brain area ceases. Instead, the researchers showed that the brain regulates activity through a process known as 'homeostatic plasticity' to 'dial up' low signals and 'dial down' high signals, similar to how a graphic equaliser on a stereo balances sound.
Dr Raffaele Tucciarelli, from the MRC Cognition & Brain Sciences Unit, said: "Although we found changes in the brain relating to behaviour – how a child compensates for their limb differences – we saw much wider changes going on due to this homeostatic plasticity. This mechanism is there to maintain stability in firing rates in the brain, to ensure brain tissue doesn't stop working from too little activity or cause a seizure from too much activity.
"This was really surprising for us. Even though we knew these regulatory processes existed, we don't tend to think of them in relation to reorganisation at this large scale, because we tend to think of this reorganisation happening as result of behaviour."
When the researchers compared the brain maps in adults born with limb differences against those from the children in the study, they found that the changes seen early in life remain largely stable into adulthood. This happens even though adults tend to rely more on their one arm and less on other body parts, suggesting the brain's layout is mostly set early on and doesn't change much in later life.
Why taking part in the research is important
Gemma Lonnon's son Noah, 11, took part in the study through the research team's 'BOLDKids' programme. Speaking about this experience Gemma said: "We first met the BOLDKids research team at a Reach family weekend in 2019. They were conducting practical tests with children who have upper limb difference, and we thought Noah, who was five at the time, might enjoy taking part.
"Since then, BOLDKids have invited Noah to take part in other studies including an online problem-solving test designed to feel like a video game and this more in-depth study which included practical problem-solving tests and a brain scan. Noah really enjoyed taking part in this research. His favourite part was going in the MRI machine and seeing pictures of his brain!
"As a family, we wanted to take part to understand how Noah's brain adapted to his limb difference. Over the years we have seen that Noah adapts quickly to problem solving and everyday tasks and activities. He comes up with practical solutions to situations that we don't see.
"Taking part was important to us. It is fascinating to see how children like Noah develop unique skills to overcome challenges. We're proud to be part of something that could help other families too."
Steve Haynes from Reach said: "At Reach Charity we're really grateful this research has been undertaken. The findings reinforce what many Reach adults have long suspected: that our brains can feel like they're wired a little differently. This study highlights the unique strengths that those with upper limb difference can bring to a world that is often not designed with them in mind."
Reference
Tucciarelli, R et al. Global remapping of the sensory homunculus emerges early in childhood development. Nat Comms; 24 Feb 2026; DOI: 10.1038/s41467-025-66539-5
The research was supported by the Wellcome Trust and the Medical Research Council, with additional support from the Czech Science Foundation. Professor Makin and Dr Tucciarelli conducted some of their work while at UCL.
