Researchers from the University of Regensburg, Germany, studied 24 people using brain scans. Half were given the task of learning to juggle, while the others were give no special task. After three months, the brains of all 24 people were scanned again. They found that the brains of the people who had learned to juggle had grown in size by 3-4% while no change occurred in the non-juggling group.
The jugglers were found to have more grey matter in the mid-temporal area and the left posterior intraparietal sulcus. Both of these brain areas are involved in the processing of visual and motor information. The researchers also found that the more skilled the jugglers had become at juggling, the greater the brain growth they experienced.
To finish up the experiments, the researchers asked the jugglers to stop practicing. A third set of scans 3 months later showed that the enlarged brain areas of the new jugglers had shrunk back down. This seems to imply a sort of use it or lose it phenomenon. Similarly, the same type of increase/decrease goes on with physical exercise so it really should be of no surprise.
If you’re interested in learning the skill of juggling, I’ve found a couple of great instructional videos below to get you started. Have fun!