Juggling boosts the connections between different parts of the brain by tweaking the architecture of the brain's "white matter" – a finding that could lead to new therapies for people with brain injuries.
White matter describes all areas of the brain that contain mostly axons – outgrowths of nerve cells that connect different cells. It might be expected that learning a new, complex task such as juggling should strengthen these connections, but previous work looking for changes in the brains of people who had learned how to juggle had onlystudied increases in grey matter, which contains the nerve cells' bodies.
Now Jan Scholz and his colleagues at the University of Oxford have discovered that juggling changes white matter, too. They gave 24 young men and women training packs for juggling and had them practise for half an hour a day for six weeks. Before and after this training period, the researchers scanned the brains of the jugglers along with those of 24 people who didn't do any juggling, using a technique called diffusion tensor imaging that reveals the structure of white matter.
They found that there was no change in the brains of the non-jugglers, but the jugglers grew more white matter in a part of the parietal lobe – an area involved in connecting what we see to how we move.
The same transformation was seen in all the jugglers, regardless of how well they could perform. This suggests that it's the learning process itself that is important for brain development, not how good you are.
Arne May of the University Medical Centre Hamburg-Eppendorf in Germany, who led the previous work on juggling and grey matter, finds this result "fascinating". "It suggests that learning a skill is more important than exercising what you are good at already – the brain wants to be puzzled and learn something new," he says.
Like May, Scholz's group found increases in grey matter, but differences in the size and timing of the grey- and white-matter changes suggest they are independent. Nevertheless, both are probably necessary to learn how to juggle, argues Scholz.
"More white matter on its own might mean you can move more quickly, but you'd need the grey matter to make sure your hands were in the right place," he says.
The group scanned the jugglers' brains again after four weeks without juggling. They found that the new white matter had stayed put and the amount of grey matter had even increased. This could be why, when we learn a new skill, we retain some ability, no matter how long ago we last practised.
"It's like riding a bike," Scholz says. "Either you can juggle or you can't. It takes a lot of training to learn, but once it clicks, you don't forget it."
Scholz also hopes that it might be possible to develop juggling-based training programmes to help people with brain injuries, or that further study of how juggling changes the architecture of the brain may lead to the discovery of drugs that could boost this plasticity. "If we could use training or drugs to help stroke patients regenerate damaged parts of their brains, that would be fantastic," he says.
Journal reference: Nature Neuroscience, DOI: 10.1038/nn.2412