Rats can bop to the beat – a trait once thought to be exclusively human

2022-11-14

Naturally recognising a beat in a song – known as beat synchronicity – is something that humans are naturally good at. Even if you’ve never heard a song in your life, the ability to bop your head or tap your feet at the right time is a trait that we take for granted.

But research has found that it’s not just a human trait. First it was Snowball, a pet sulphur-crested cockatoo, who went viral a decade ago for his headbanging and ended up the star of a paper in Current Biology.

Now, researchers have published a paper in Science Advances showing that rats also have the ability to recognise beats, and the finding might help scientists understand the mechanism behind how this occurs in humans.

“Rats displayed innate — that is, without any training or prior exposure to music — beat synchronisation most distinctly within 120-140 bpm (beats per minute), to which humans also exhibit the clearest beat synchronisation,” explained biomedical engineer Associate Professor Hirokazu Takahashi from the University of Tokyo.

“The auditory cortex, the region of our brain that processes sound, was also tuned to 120-140 bpm, which we were able to explain using our mathematical model of brain adaptation.”

The researchers attached an accelerometer to the head of 10 rats, and then played music for them. The rats listened to 60 second excerpts of ‘Sonata for Two Pianos’ in D major, by Mozart.

They played at four different tempos — 99 BPM (which is 75% of the original), 132 BPM (normal speed), 264 BPM (twice the original), and 528 BPM (four times the original).

The accelerometers allowed the researchers to measure the slightest head movements in the rats. They also did the research in 20 human participants, with accelerometers attached to headphones.

The team found that just like humans, the 132 BPM version was the one that the beat was most understood, and the rats’ beat synchronicity was clearest.

This is a little surprising, as rats are generally a lot ‘faster’ than humans. Their heartbeat, breathing rate, circulation time and lifespan are all shorter, and so the team thought that maybe the ideal tempo would be faster as well.

Instead, the similar BPM result means that maybe the speed is determined by something called the brain ‘time constant’, suggesting that our ability to keep the beat has been conserved in the brain waves of both humans and rats.

“After conducting our research with 20 human participants and 10 rats, our results suggest that the optimal tempo for beat synchronization depends on the time constant in the brain,” said Takahashi.

“This demonstrates that the animal brain can be useful in elucidating the perceptual mechanisms of music.”

Although this might just seem like a cute, unimportant experiment, understanding why only some animals – including rats – seem to be able to understand beats will help us get to the bottom of why music is so important to us… and Snowball the cockatoo.

Cosmos, 11 November 2022
; https://cosmosmagazine