How Scientists Map the Brain

Scientists map the brain the way cartographers once mapped the world: no single survey does it all, so they combine methods that each capture a different layer. Some techniques reveal what the brain is made of, others show where regions begin and end, and still others trace the connections between them. A modern brain atlas is really a stack of these maps laid on top of one another.

Mapping structure: what the brain is made of

The oldest brain maps came from slicing and staining tissue under a microscope. More than a century ago, Korbinian Brodmann divided the cortex into numbered areas based on differences in its cellular layers, and his map is still cited today. Structural MRI now does something similar in living people, capturing the folds, thickness, and boundaries of the cortex without a single cut.

Mapping activity: what the brain is doing

To see the brain in action, researchers watch it work. Functional MRI tracks blood flow as a stand-in for neural activity, lighting up regions that engage during a task, while EEG reads the brain's electrical rhythms directly through the scalp. These methods do not show wiring, but they reveal which areas tend to fire together, which hints at how they are linked.

Mapping connections: how regions link up

The hardest thing to map is the wiring itself. In animals, the gold standard is tract-tracing: a chemical injected into one region travels along neurons and reveals exactly where they reach. In living humans, where injections are not an option, diffusion MRI and tractography infer the major white-matter tracts by tracking how water moves along nerve fibers. Tractography is powerful but indirect, and it can miss real pathways or invent ones that are not there, which is why animal tracer data remains the benchmark.

Why animal brains are part of human brain maps

Because we cannot trace connections invasively in people, much of our knowledge of brain wiring comes from other species, especially monkeys. Decades of macaque and marmoset tracer studies have been gathered into shared connectivity databases, such as CoCoMac, that let researchers compare and cross-check results. Curating that primate connectivity literature, matching regions across studies and standardizing the references, is the kind of groundwork brainmeta grew out of, and it is part of what makes human brain maps possible at all.

Putting the layers together

No single method wins. The best modern brain atlases combine structure, activity, and connectivity, aligning them to a shared reference template so that a spot on one map means the same thing on another. The result is less a single picture than a layered map you can zoom into and switch between, and it keeps improving as the tools sharpen. Brain mapping also underlies a lot of what shapes personality and behavior: for the wiring side of one well-studied trait, see our piece on the neuroscience of introversion and extraversion, or read about the connectome for the map of the brain's connections.