How to see a memory

This collection of work from multiple groups has built a strong case that the physiological trace of a memory — or at least key components of this trace — can be pinned down to specific neurons, says Silva. Still, neurons in one part of the hippocampus or the amygdala are only a tiny part of a fearful foot-shock engram, which involves sights, smells, sounds and countless other sensations. “It’s probably in 10–30 different brain regions — that’s just a wild guess,” says Silva.