A report in the journal Nature compared brain-imaging scans of non-jugglers who were taught to juggle and a control group. Three months after, scans showed that the grey matter of the new jugglers increased in the areas of the brain that processes and stores visual information. Scans done three months after they stopped juggling showed that the grey matter had been reduced. So...the concept of using our brain or losing it becomes even more accurate.
Separately, the work I do with Brain Gym(r) has been proven to make changes in brain function. You can learn more by going to www.BrainGym.org.