The brain looks like a featureless expanse of folds and bulges, but it’s actually carved up into invisible territories. Each is specialized: Some groups of neurons become active when we recognize faces, others when we read, others when we raise our hands.

On Wednesday, in what many experts are calling a milestone in neuroscience, researchers published a spectacular new map of the brain, detailing nearly 100 previously unknown regions — an unprecedented glimpse into the machinery of the human mind.

Scientists will rely on this guide as they attempt to understand virtually every aspect of the brain, from how it develops in children and ages over decades, to how it can be corrupted by diseases like Alzheimer’s and schizophrenia.

“It’s a step towards understanding why we’re we,” said David Kleinfeld, a neuroscientist at the University of California, San Diego, who was not involved in the research.