Juggling and probably other visual skills that take time to master increase the size of your brain.
That's the conclusion of German researchers, which throws down the gauntlet to the mainstream view that the size of the adult brain does not change at all except when it is confronted by ageing or disease.
University of Regensburg neurologist Arne May and colleagues asked 12 people in their early 20s, most of them women, to learn a classic three-ball juggling trick over three months until they could sustain a performance for at least a minute.
Another 12 were a control group who did not juggle.
All the volunteers were given a brain scan with magnetic resonance imaging at the start of the programme, and a second after three months.
After this, the juggling group were told not to practise their skills at all for three months, and then a third scan was taken of all 24 volunteers.
The scans found that learning to juggle increased by about 3 per cent the volume of "grey matter" in the mid-temporal area and left posterior intra-parietal sulcus, which are parts of the left hemisphere of the brain that process data from visual motion.
Students who had not undergone juggling training showed no such change.
After the third scan, by which time many recruits had forgotten how to juggle, the increases in grey matter had partly subsided.