Nathan Hesselink had never heard any of Radiohead's music — a bit unusual, perhaps, for an ethnomusicologist who spends his life immersed in music and studying the people who make it.

But in 2008, the band was billed to play a concert at the football stadium on the campus of the university in Vancouver where Professor Hesselink worked.

Tickets had been sold out for months, but as he watched the crowd build throughout the afternoon, he realised that this was his chance.

"I just thought, 'I've got to go out and hear Radiohead play live'."

In spite of drenching rain, Professor Hesselink and his wife and 10-year old son joined hundreds of other people to listen to the concert from outside the arena.

"It was just so fascinating hearing the band," he said.

"There was a lot going on with the music that maybe I wasn't expecting or I hadn't prepared myself for."

He was hooked. But perhaps unusually for a Radiohead fan, it wasn't the preternatural vocals, the dystopian lyricism, or even the experimental instrumentation that got him in. It was the rhythm.

Professor Hesselink specialises in studying the irregular beats in South Korean folk music.

South Korean folk percussion rhythms are created by drums and gongs. ( Supplied: US Army/Edward N. Johnson )

Transfixed by the rhythms in Radiohead's music, he wanted to know more about the band.

"[The concert] led to me pretty much the next week going out and finding all of their music on CD, and then starting to work my way through their music."

His approach to the Radiohead back catalogue was meticulously academic. He started with album one, Pablo Honey, track one, You, and listened through the album in order, over and over again, only moving on to album two, The Bends, once he was convinced he'd gained a full appreciation for the debut.

Then he started making sketches of the more rhythmically interesting songs.

"It was incredibly time consuming, of course. It sort of drove my family crazy because they would hear the same song or the same album over and over like they couldn't escape it."

And for a while, this highly structured journey of Radiohead discovery continued just like this; song after song, album after album. But then, he arrived at album five, Amnesiac, track two, Pyramid Song.

"When I got to that song, it completely threw me for a loop," he said.

"Right away with that song, it just has that one little stutter in the one chord that makes it impossible to tap your hand or your foot perfectly in time until you've gotten used to it — but it's not a regular pulse. That's just so unusual in any genre of popular music."

Loading...

Professor Hesselink was so stumped by the song, he went searching for answers online — not something he often did back in 2008.

Like turning up to the Radiohead concert and finding hundreds of other people crowded outside the stadium, he stumbled upon entire nooks of the internet overrun by warring tribes of Radiohead fans, each staunch in the belief that their interpretation of the Pyramid Song rhythm was the correct one.

"There were a lot of other people talking about the melody and the lyrics and why is it called Pyramid Song. But it was that rhythm discussion that I just couldn't believe that that many people were getting into it," Professor Hesselink said.

"I thought, 'You know what? I'm going to try to actually figure out what all these people actually mean'."

Why are humans so rhythm obsessed?

The compulsion to tap along to a beat — something scientists call entrainment — is unique to humans and emerges quite early in childhood.

While some other animals can synchronise with a steady, metronomic beat, they can't tap along to anything more complex, like music.

Neuroscientist and classically trained pianist Sylvie Nozaradan of Western Sydney University studies how our brains perceive and respond to music.

"When we talk about entrainment to music it usually refers to the spontaneous ability we have to move our body to the beat of the music," Dr Nozaradan explained.

Dr Nozaradan uses electroencephalogram (EEG) recordings to peer inside our brains as they're locking onto a beat. The EEG is recorded in real time, which allows her to directly link what's happening in the brain to whatever's going on in the music.

By comparing what happens when people listen to music without moving with when they are asked to tap along to beat, her experiments show our brains have an inbuilt metronome.

Surprisingly, not only do our feet tap to the beat, but neurons in our brain fire away in time with rhythms.

"If we present the participants with a simple metronome, and we record EEG, it's quite logical that we will find a peak of neural activity at the frequency of the metronome," Dr Nozradan said.

"But when we present more complex music, like the music we hear in our everyday life, we still find this peak of neural activity precisely at the beat frequency."

And even when the beat drops out our brain keeps pulsing as if the beat was still there.

Why and how we developed this ability to instinctively synchronise to a beat is highly debated. Some have argued that it's related to our brain anatomy. The network of brain regions that allows us to synchronise to a beat is the same network that gives us our capacity for speech. And the connections between these two abilities might have ancient origins.

"One of these theories argued that speech evolved as a byproduct of music," Dr Nozaradan said.

"As first humans we sang and communicated with some forms of primitive drumming, and then it evolved into more complex sound communication, which turns out to be our speech now."

But what do we like to listen to?

Even if our brains have evolved the capacity to instinctively pulse along to a beat, that doesn't tell us much about the type of music we enjoy listening to.

"When a rhythm is very simple it's quite boring," Dr Nozaradan said.

"We can synchronise with it, but it's not very interesting. When the rhythm is too complex, on the other hand, it's also boring because we can't really catch the beat. So there is a compromise between simplicity and complexity."

This is the concept of rhythmic ambiguity. Our brains seem primed to enjoy patterns of beats that are a bit more interesting than a regular four-to-the-floor metronomic beat, but not so complicated you can't find the beat at all.

African rhythms combine different patterns of beats. ( Supplied: USAID/Kasia McCormick )

Andy Milne, a colleague of Dr Sylvie Nozaradan, believes these rhythmically ambiguous zones can be a creatively rich space for musicians.

"What the artist is attempting to do is to find a sort of a Goldilocks zone in the middle where you're presenting the listener something which is complicated, but not so complicated they can't understand it," said Dr Milne, who researches the rhythms that capture our attention.

Dr Nozaradan's EEG data shows our brain's built-in metronome ticks loudest in this rhythmically ambiguous zone.

"When a rhythm is very simple we have a very clear activity, but it's not as big as what we would find in a more complex rhythm," she said.

"But again, when the rhythm is too complex, the activity is, again, smaller. So there's a compromise. It's like the brain locks more easily when it's slightly complex, but not too much."

Dr Milne uses maths to make beats that fall squarely within the Goldilocks Zone of rhythmic ambiguity such as the polyrhythms you hear in African drumming where two different patterns are played simultaneously.

Loading...

"If you've got four beats running, and you've got three beats running at the same time, then although one of them can coincide, the other two of the three beats cannot coincide with the others," Dr Milne said.

"You can count the four, or you can count the three or you can just, sort of, hear the totality of it. So, you get this sort of interlocking pattern."

So what's this got to do with Radiohead's Pyramid Song?

Radiohead's Pyramid Song sits squarely in the Goldilocks zone of rhythmic ambiguity; its rhythm is more complicated than a simple metronome, but not so complicated we can't find the beat at all. Which might explain why Professor Hesselink was compelled to go searching for answers online.

When he studied the Radiohead fans using Western music theory he found that, when you take out all the fringey outlier views, two main tribes formed in the Pyramid Song debate.

"Basically, the one camp is saying the song to them sounds more like a typical rock song, then the other camp really felt that the song was more jazz inflected."

Personally, Professor Hesselink is Team Jazz.

"I hear the jazz inflection in the song," said Dr Hesselink. "But it's not important that anyone agrees with me."

To hear more extraordinary stories from the world of numbers, subscribe to the Sum Of All Parts podcast.