A new study (2008) just published in PLoS One reports that learning to juggle alters the structure of motion detection areas in the brain within as little as 7 days. 

Led by neuroscientist Joenna Driemeyer, the study builds on a previous research that also found juggling could alter brain structure, although this previous study waited three months before the brain was checked for alterations using high resolution structural MRI scans. 

This new study also took 20 non-jugglers and asked them to learn to juggle, but scanned them after 7, 14 and 35 days. 

After only 7 days, a motion specialized part of the occipital lobe known as V5 had increased in density. In both studies, the changes were maintained over the subsequent weeks of practice, but these areas returned to their pre-learning state after several weeks without juggling. 

This is an interesting example of rapid ‘neuroplasticity‘, the ability of the brain to adapt structurally to new situations. 

However, the authors are careful to note that they can’t tell whether the brains of the participants had generated more neurons, or whether existing cells grew in size, or additional glial cells were developed, or maybe there were just changes in how much blood or other brain fluids packed the area. 

Also, the fact that changes seemed to occur at the beginning of the learning cycle but that further practice maintained but didn’t cause additional changes led the researchers to speculate that learning a variety of new things, rather than simply practicing old skills, may be most effective in terms of brain structure alterations.