In Brain part 1 and Brain part 2, we’ve talked about how every brain is a bit different—and how it keeps changing throughout life. But how do scientists study these differences? And if everybody is different how do they know what’s “normal” in the first place?
One way is by comparing a person’s brain shape to a standard “template” brain. Researchers look at how much certain parts of the brain need to stretch or shrink to match the template. This helps them spot which parts tend to vary the most between people. They even use colorful maps to show where these differences happen.
Another method is using “brain charts”— a bit like the growth charts doctors use to track a child’s height or weight. These charts show what’s common for things like brain size or thickness at different ages. If someone’s brain looks very different from the chart, it might mean there’s something to look into.
But here’s the catch: most of these methods treat healthy brain variability as small changes around an average. That might seem reasonable—until you think about what averages really mean.
Here’s an example: let’s say you have 10 friends. Five of them each have 5 candies, and five have just 1. The average is 3 candies—but no one actually has 3. That middle number doesn’t reflect anyone’s real experience. The same thing can happen when we talk about the “average brain.” It might not represent how any one person’s brain actually works.
So while brain templates and charts help scientists see broad trends, they don’t capture the full picture of what makes each brain unique.
Figuring out what counts as common, what’s truly unique, how much variation matters, and how a shared pattern show up differently in individual brains—that’s a challenge that still puzzles philosophers and researchers today.
Recommended reading
- Croxson PL, Forkel SJ, Cerliani L, Thiebaut de Schotten M. Structural Variability Across the Primate Brain: A Cross-Species Comparison. Cereb Cortex. 2018 Nov 1;28(11):3829-3841. doi: 10.1093/cercor/bhx244. PMID: 29045561; PMCID: PMC6887925.
- Ge R, Yu Y, Qi YX, Fan YN, Chen S, Gao C, Haas SS, New F, Boomsma DI, Brodaty H, Brouwer RM, Buckner R, Caseras X, Crivello F, Crone EA, Erk S, Fisher SE, Franke B, Glahn DC, Dannlowski U, Grotegerd D, Gruber O, Hulshoff Pol HE, Schumann G, Tamnes CK, Walter H, Wierenga LM, Jahanshad N, Thompson PM, Frangou S; ENIGMA Lifespan Working Group. Normative modelling of brain morphometry across the lifespan with CentileBrain: algorithm benchmarking and model optimisation. Lancet Digit Health. 2024 Mar;6(3):e211-e221. doi: 10.1016/S2589-7500(23)00250-9. PMID: 38395541; PMCID: PMC10929064.
