Have you ever noticed how your body naturally syncs to a beat—tapping a foot to music, matching your pace to a walking partner, or getting drowsy during a steady train ride? That “syncing” tendency has a scientific name: entrainment . And researchers are now exploring whether the brain can be gently guided by rhythm too—especially at a frequency that keeps showing up in neuroscience: 40 hertz (40-Hz) . Why 40-Hz matters Forty hertz sits in the range of faster brain rhythms so