为什么有些音乐让人想跳舞?

DAVID GREENE, HOST: Have you ever wondered why some songs just make you want to dance? Like Pharrell's song, "Happy," for example.

(SOUNDBITE OF SONG, "HAPPY")

PHARRELL WILLIAMS: (Singing) Clap along if you feel like a room without a roof.

GREENE: It got people dancing on video all around the world. Well now scientists have a theory about why certain songs have this effect. NPR's Michaeleen Doucleff reports.

MICHAELEEN DOUCLEFF, BYLINE: Maria Witek is a brain scientist. She studies people's emotions at Aarhus University in Denmark. But she also likes music, especially if it's groovy.

MARIA WITEK: The Meters are pretty funky. I like The Meters.

(SOUNDBITE OF SONG, "HAND CLAPPING SONG")

THE METERS: (Singing) Clap your hands now, people clap now. Clap your hands now, people clap your hands.

DOUCLEFF: So that's The Meters' "Hand Clapping Song" from 1970, and just like Pharrell's "Happy," it triggers a nearly uncontrollable need to tap your foot, bob your head - move to the rhythm in some way, and Witek thinks she knows why. Last month, Witek and her colleagues published a study showing that songs like these have just the right amount of gaps or breaks in the beat. She says your brain wants to fill in those gaps with body movement.

WITEK: Gaps in the rhythmic structure - gaps in the sort of underlying beat of the music - that sort of provides us with an opportunity to physically inhabit those gaps and fill in those gaps with our own bodies.

DOUCLEFF: A few years ago, Witek set out to figure out which songs get people out on the dance floor. She created an online survey and gave people drum patterns to listen to. Some had really simple rhythms with regular beats.

(SOUNDBITE OF SIMPLE BEATS)

DOUCLEFF: Others had very complex rhythms with lots of gaps where you expect the beats to be.

(SOUNDBITE OF COMPLEX BEATS)

DOUCLEFF: Finally, there were drumming patterns that fell in the middle of the two extremes. They have a regular predictable beat, but also some pauses or gaps. Witek says that people all over the world agreed about which drum patterns made them most want to dance.

WITEK: Not the ones that had very little complexity, and not the ones that had very, very high complexity, but the patterns which had sort of a balance between predictability and complexity. So, where there's enough regularity to sort of perceive the underlying beat, but also enough complexity to sort of invite participants to synchronize to the music.

DOUCLEFF: So I asked Witek, which popular songs today have just the right amount of complexity?

WITEK: I think the recent single by Pharrell, "Happy," is a very good example.

(SOUNDBITE OF SONG, "HAPPY")

WILLIAMS: (Singing) It might seem crazy, what I'm 'bout to say...

DOUCLEFF: Witek says the song is layered with predictable beats and syncopated ones. The drums, the piano, the clapping - even Pharrell's voice creates inviting gaps.

(SOUNDBITE OF SONG, "HAPPY")

WILLIAMS: ...With the air, like I don't care baby by the way...

DOUCLEFF: But Pharrell isn't the only one who knows about this trick. Witek says classic dance tunes in disco, funk, hip-hop and R and B also hit this sweet spot of syncopation.

WITEK: Michael Jackson, Stevie Wonder - I have a lot of tracks which seem to have this balance between predictability and complexity when it comes to the rhythmic structure.

DOUCLEFF: Not to mention, Ray Charles.

(SOUNDBITE OF SONG, "I GOT A WOMAN")

RAY CHARLES: (Singing) Well, I got a woman way over town...

DOUCLEFF: "I Got A Woman" made everybody hit the dance floor in the 1950s. Neuroscientist, Daniel Levitin at McGill University, says it's not just the song's syncopation, but also the layers of rhythm - layers that get you to go from just tapping your foot in your chair to standing up and full out dancing.

(SOUNDBITE OF SONG, "I GOT A WOMAN")

CHARLES: (Singing) She gives me money when I'm in need...

DANIEL LEVITIN: The drums are keeping a very steady rhythm, the piano is syncopated, the vocals are exquisitely nuanced in the time. It's very difficult to sing along with it exactly the way he does it.

DOUCLEFF: So we don't want to sing with Charles. We want to move with him.

LEVITIN: The more rhythmically complex the music is, the easier it is to engage different body parts because they can be synchronizing to different aspects of the music.

DOUCLEFF: You're swinging your shoulders with the snare drums, you're bobbing your head with the piano.

LEVITIN: And you might be wiggling your hips in half-time or something like that.

DOUCLEFF: Before you know it, you're up out of your chair and doing the twist. Michaeleen Doucleff, NPR News, San Francisco.