Scientists examined 545 top-selling pop songs from more than three decades

They found that the key to the perfect pop song is a sudden chord change

This triggers a rush of dopamine in the brain similar to that created by sex

Record bosses have spent millions trying to create the perfect pop song.

They find heart-throb singers who will set teenagers' hearts aflutter, employ teams of lyricists, and demand a tune catchy enough to guarantee weeks of airplay.

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But the key to a smash hit may be far more simple, as classic bands like the Beatles and Beach Boys know all too well.

To achieve greatness, a song needs a sudden chord change, according to US neuroscientists who examined 545 top-selling pop songs from more than three decades.

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Record bosses have spent millions trying to create the perfect pop song. They find heart-throb singers who will set teenagers' hearts aflutter, employ teams of lyricists, and demand a tune catchy enough to guarantee weeks of airplay

WHAT MAKES THE PERFECT SONG? The study analysed chord-by-chord transcriptions of the harmonies of 545 songs that entered the American Billboard Hot 100 charts between 1958 and 1991. The resarchers measured how far the chords of the song deviated from what was expected. For example, C major is usually followed by G and F major in Western tonal music and a change from this would be classed as a surprise. These measures of surprise were compared throughout the entire song and between song sections. The team then used the peak position of the song in the weekly Billboard Hot 100 chart to determine its popularity. It revealed that verses, not the choruses or bridges, accounted for much of the difference in harmonic surprise between the most and least popular songs in the Billboard Hot 100 chart. The researchers suggest that high surprises in the harmony of a song, as well as high surprises followed by a lower-surprise section, can both contribute to the enjoyment of an unfamiliar piece of music.

An unexpected chord change is thought to trigger a rush of dopamine in the brain similar to that created by food and sex.

This is the moment when people get 'chills' from a song, and the technique is used by the Beach Boys in the first 10 seconds of Wouldn't It Be Nice as well as in the final chorus of the Beatles' classic Penny Lane.

The US researchers present their findings in the journal Frontiers in Human Neuroscience.

Co-author Norberto Grzywacz, professor of neuroscience at Georgetown University in Washington, said: 'We evaluated the role of a compositional element - the harmonic surprise.

'Surprise is important because it is a measure of new information - something that the reward centres of the brain recognise as being of value, leading to a positive emotional response.

'Therefore, our finding that the most popular songs tend to include surprising chords reflects our brain's in-built preference.'

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The study took the harmonies of the top 100 songs in the charts between 1958 and 1991, analysing their harmonies chord by chord.

To select their sample, they chose songs only in a major key, and judged their popularity based on their chart ranking for record sales and airplay.

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The key to a smash hit may be far more simple, as classic bands like the Beatles and Beach Boys (pictured) know all too well

The team measured how far the chords of the song deviated from what was expected, such as the popular Western chord progression from a C major chord to G and F major.

Professor Grzywacz said: 'The most popular songs tend to include relatively rare chords - that is, they typically have high harmonic surprise.

'These songs also tend to have choruses with relatively low harmonic surprise preceded by sections with many rare chords.'

The researchers found that the most popular songs tend to include relatively rare chords, that is, they typically have high harmonic surprise. Pictured are The Beatles

However it seems we don't like our pop music too unpredictable, so part of the reward in the brain comes when the sudden chord change returns to normal.

The neuroscientist added: 'The brain enjoys surprise only up to a point, because unexpected events indicate a failure of prediction.

'Hence, the release of tension from surprising sections of a song to common choruses is also signalled positively by the reward centres. Our research reveals that the brain has a deep-rooted preference, which can affect whether people enjoy a piece of music.'

The researchers suggest that harmonic surprises - unexpected changes in structure - can increase the likelihood a song will be a hit. Pictured is Micahel Jackson

The researchers suggest that high surprises in the harmony of a song, as well as high surprises followed by a lower-surprise section, can both contribute to the enjoyment of an unfamiliar piece of music. Pictured is Whitney Houston

The most popular songs are believed to release the same 'happy hormone', dopamine', as novelty-seeking behaviours such as drug-taking or casual sex.

Brain scans have previously shown dopamine is released when people hear sections of music that evoke the 'chills', such as a chord change followed by a predictable harmony.

MUSIC CAN CHANGE THE TASTE OF FOOD University of Oxford psychologist Charles Spence has previously explored an effect he calls 'digital seasoning', in which different musical genres can change your the taste of your takeaway. The research found some music genres can enhance the taste of a meal while others seem to have a detrimental impact on the experience. Indie rock bands like the Arctic Monkeys complements the spice in a curry. Pop music such as Ed Sheeran's hit Sing, or Taylor Swift's Blank Space is perfect for Chinese. Opera favourite Nessun Dorma, and classical music, such as Vivaldi, boosted the tastiness of Italian food. Jazz, along with classics by Sinatra and Nina Simone were best for Sushi and Thai Dance. Hip hop either has no effect or a detrimental effect on the expected enjoyment of food. But look away Justin Beiber fans: the Canadian star's hit song Baby had a detrimental effect on the enjoyment of pretty much every dish in the study.

The new study revealed that verses, not the choruses or bridges, most often produced the chord change behind the most popular songs in the US charts – the Billboard Hot 100.

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The researchers will now examine whether a song has to have different chord changes to historic pop songs to provide the same brain hit.

Professor Grzywacz said: 'Our overall goal is to use this knowledge to develop a general theory of how the brain experiences beauty in art.'