Roughly 90% of people experience 'earworms' — songs that lodge in the mind and repeat involuntarily. Brain scans show they activate the same neural circuits as actual music, as if your brain is literally playing the song in real time. This isn't a bug in human cognition. It reveals something deep about how memory works.

Music is processed in more regions of the brain than almost any other stimulus. Rhythm activates motor areas — which is why you tap your foot involuntarily. Melody engages the auditory cortex. Lyrics engage language regions. Emotional content activates the limbic system. Unlike most experiences, which fade when attention shifts, music recruits so many systems that it creates unusually vivid, persistent memories.

This is why music is uniquely powerful for people with severe memory loss. Alzheimer's patients who can no longer recognize their own spouses often remember the words and melodies of songs from their youth. Musical memory is stored differently from autobiographical memory, in brain regions that are among the last to be damaged by dementia. Caregivers have started using personalized playlists as treatment, and the results can be remarkable — patients briefly return to themselves when their favorite songs play.

Music also synchronizes brains. When musicians play together, their brain waves literally align. Studies using EEG show that improvising jazz musicians, in particular, enter shared neural states that don't happen during normal conversation. Something similar happens at concerts — the audience's brain activity synchronizes around the music, which may explain why live shows feel more powerful than recordings.

The emotional effects are neurochemical. Listening to music you love releases dopamine, the same neurotransmitter involved in food, sex, and drug use. The peak emotional moments in a song — what music psychologists call 'frisson' — trigger measurable dopamine spikes. This is chemically the same pleasure as eating chocolate or falling in love, just produced by patterns of sound waves.

The evolutionary origin of all this is still debated. Music predates written history; bone flutes have been dated to over 40,000 years ago. Some researchers argue music evolved as a social bonding mechanism. Others think it was a side effect of language. Darwin himself speculated it was for mate selection.

Whatever the origin, music hijacks some of the most sophisticated circuitry in the human brain. No wonder it can haunt you.