In 2004, a small study at the University of Regensburg quietly rewrote the popular understanding of the adult brain. The team took 24 non-jugglers, taught half of them a basic three-ball cascade, and scanned everyone with high-resolution MRI before and after.
The result was published in Nature under a deliberately understated title: “Neuroplasticity: Changes in grey matter induced by training.” It became one of the most cited pieces of evidence that adult brains remain structurally plastic.
What the paper actually shows - and what later research has clarified - is more specific than the headlines.
The 2004 study: what was measured
Draganski and colleagues used voxel-based morphometry, a technique that compares grey matter density at every point in the brain across two scans. The jugglers practised the cascade until they could sustain it for at least 60 seconds. After three months, two regions showed reliable increases of roughly 3-5%: the mid-temporal area, known as V5/MT, and the posterior intraparietal sulcus.
These are not general cognition regions. V5/MT is the brain’s primary visual motion processing area - it computes the trajectory of moving objects in your visual field. The posterior intraparietal sulcus integrates that motion information with the planning of arm and hand movement. The brain grew, in effect, exactly where juggling demands it grow.
Three months later the researchers scanned again, with practice paused. The grey matter changes had partially reversed.
What the white-matter study added
Five years after the 2004 paper, an Oxford group led by Jan Scholz used a different technique - diffusion tensor imaging - to look at white matter rather than grey. White matter is the brain’s wiring: bundles of myelinated axons that carry signals between regions.
In a 2009 Nature Neuroscience paper, Scholz et al. trained 24 adults to juggle for six weeks and found measurable increases in white matter coherence in the right intraparietal sulcus. Importantly, the changes appeared whether or not jugglers became proficient. The structural adaptation tracked time spent practising, not skill achieved.
This pairs with the grey-matter finding in a way worth noticing: juggling produces both denser cortical tissue in motion-processing regions and stronger connectivity between them. The brain restructures both the nodes and the wires.
The age question
A persistent assumption is that neuroplasticity is mostly a young-brain phenomenon. The juggling literature contradicts this directly.
Boyke and colleagues (2008) ran the Draganski protocol with adults aged 50-67. The grey matter increases in V5/MT were comparable to those seen in younger participants. A 2022 systematic review by Vetter and colleagues, looking across 11 juggling-training neuroimaging studies, found structural changes consistently across age groups, including participants over 60.
Older brains learn the cascade more slowly. The required practice volume is higher, and the proficiency curve is shallower. But the structural response is intact.
The brain restructures itself in response to current demand, not chronological age. Stop the demand and the structure begins to retreat - at any age.
Process, not expertise
One of the more surprising findings across these studies is that the brain changes are not driven by skill level. Participants who never achieved a clean cascade still showed measurable structural adaptation. The act of repeated, effortful practice produced the change, regardless of how successful any given attempt was.
For the Draganski study, the criterion was sustaining a cascade for 60 seconds. Many participants struggled to reach this. Their brains changed anyway. In the Scholz et al. follow-up, this was made explicit: white matter changes correlated with hours practised, not with cascade duration achieved.
This has practical implications. The neural benefit of learning a hard motor skill comes from the struggle, not the mastery. The dropped balls are not failures of the practice - they are the practice.
What this does and does not tell us
The temptation is to round these findings up to “juggling makes you smarter.” That overstates what the evidence supports.
The structural changes are region-specific. They affect motion tracking, motor sequencing, and the connectivity between visual and motor systems. They do not show transfer to unrelated cognitive domains - working memory, language, abstract reasoning.
What juggling demonstrates, with unusual rigor, is that adult cortical structure is responsive to specific, sustained practice. The mechanism is real. The benefit is local. The maintenance is ongoing.
That is a smaller claim than the popular reading of the literature, and it is also a more useful one. If you want to grow the parts of the brain that handle moving objects and rapid motor planning, juggling is one of the cleanest experimentally validated methods we have.
Further reading
- Draganski, B., Gaser, C., Busch, V., Schuierer, G., Bogdahn, U., and May, A. (2004). “Neuroplasticity: Changes in grey matter induced by training.” Nature, 427(6972), 311-312.
- Scholz, J., Klein, M.C., Behrens, T.E.J., and Johansen-Berg, H. (2009). “Training induces changes in white-matter architecture.” Nature Neuroscience, 12, 1370-1371.
- Boyke, J., Driemeyer, J., Gaser, C., Buchel, C., and May, A. (2008). “Training-induced brain structure changes in the elderly.” Journal of Neuroscience, 28(28), 7031-7035.
- Driemeyer, J., Boyke, J., Gaser, C., Buchel, C., and May, A. (2008). “Changes in gray matter induced by learning - revisited.” PLOS ONE, 3(7), e2669.
- Vetter, P., et al. (2022). “Systematic review of structural brain changes following juggling training.” Available via PubMed Central.