If you distil this study down to its essence, the conclusion is “the structure of a perfect pop song requires surprise.” But what does that structure include? Unexpected chord changes, apparently. They call it “harmonic surprise,” the kind of thing you find in the Beatles’ “Penny Lane” or in a variety of songs by the Beach Boys. If you want something more specific from a music theory point of view would be a deviation from the standard C-major, F-major, G-major progression.
This is from Neuroscience News:
Think of your favourite pop song. Can you explain why you like it so much? It might remind you of a memorable event, or move you in a way that makes you feel happy or sad. A new study, published in the open-access journal Frontiers in Human Neuroscience, has uncovered a simple, measurable explanation that can determine your preference for one song over another. It has linked the harmonic structure of pop songs to their placement in the charts.
“The most popular songs tend to include relatively rare chords, that is, they typically have high harmonic surprise,” says Norberto Grzywacz, a Professor of Neuroscience and Physics, who conducted this research at Georgetown University, Washington, USA. “These songs also tend to have choruses with relatively low harmonic surprise preceded by sections with many rare chords.”
Harmonic surprise can be described as where the music deviates from the listeners expectations. Scientists have predicted that these changes in structure could elicit a pleasurable reward response in the brain. In other words, harmonic surprise can increase the likelihood a song will be a hit.