Your brain runs on waves

In 1929 the German doctor Hans Berger recorded the first human brain waves, tiny rhythmic electrical signals measured through the scalp. Today we know that groups of neurons fire in rhythms, and that individual neurons respond most strongly to certain frequencies, a little like a guitar string that vibrates most at its own note.

Physicists call this resonance. It's a useful picture for thoughts too: some voices "resonate" with us because they match something we already fear or believe. Noticing that match is the first step to turning the volume down.

Sources: Berger, Archiv für Psychiatrie und Nervenkrankheiten, 1929; Hutcheon and Yarom, Trends in Neurosciences, 2000.