Rats 'bop' their heads to Mozart, proving not just humans have rhythm

A new study published today (Nov. 11) in Science Advances indicates that rats possess the ability to move to music- a capability which, before now, was believed to be unique to humans.

This fresh finding not only challenges our knowledge of the animal mind, it could also shed light on the evolution of music and dancing.

The rats 'bopped' their heads, like humans, to Mozart's Sonata

Wireless, tiny accelerometers that could detect even the slightest head movements were implanted in the rats. Additionally, participants' heads were equipped with accelerometers. Then, one-minute snippets from Mozart's Sonata for Two Pianos in D Major (K. 448) were performed at four different tempos: 75, 100, 200, and 400 percent of the original speed.

While the original tempo of the songs in Mozart's Sonata is 132 bpm, the results showed that the rats' beat synchronicity was clearest within the 120-140 bpm range. Interestingly, the researchers explained that this beat range is identical to the rate at which humans also exhibit the clearest beat synchronization.

The rats also liked Born this way by Lady Gaga amongst other hits

Other musical pieces were also played to the human and animal participants: Born This Way by Lady Gaga, Another One Bites the Dust by Queen, Beat It by Michael Jackson and Sugar by Maroon 5.

Additionally, the team discovered that both rats and people jerked their heads to the beat at similar times, and that the amount of head jerking reduced the faster the music was played.

What is 'beat synchronization'?

While animals may react to sound, create rhythmic noises, or be trained to respond to music, these behaviors are not the same as the sophisticated brain and motor mechanisms that allow humans to instinctively detect the beat of a song, react to it, or even predict it. This trait is known as beat synchronicity.

This skill appears to be partly influenced by our innate genetic ability, previously believed to be a uniquely human attribute. Amongst other cases of animals displaying beat synchronicity, this study from the University of Tokyo offers proof that rats, too, appear to share our desire to groove.

"Rats displayed innate — that is, without any training or prior exposure to music — beat synchronization," said Associate Professor Hirokazu Takahashi from the Graduate School of Information Science and Technology.

Takhashi also claimed, “To the best of our knowledge, this is the first report on innate beat synchronization in animals that was not achieved through training or musical exposure.”

Addressing the rat in the room: Why are scientists playing music to rats?

Well, it sounds excellent that rats have rhythm and all, but why would you play music to rats anyway? What's the significance? Takahashi explained that "music exerts a strong appeal to the brain and has profound effects on emotion and cognition. To utilize music effectively, we need to reveal the neural mechanism underlying this empirical fact."

Takahashi further disclosed that he is an expert in the field of electrophysiology, which examines the electrical activity of the brain, and has spent many years researching rats' auditory cortexes, which are the parts of the brain responsible for processing sound.

This makes sense, considering that part of the study involved tuning the rats' auditory cortex to match certain beats per minutes (bpm).

'Understanding the perceptual principles of music can benefit from studying the animal brain'

The team came up with two theories to explain what beat synchronization depends on: The first suggested that the 'body's' time constant would determine the ideal musical pace for beat synchronization. This varies between species and happens much more swiftly for small animals than humans (think of how quickly a rat can scuttle). 

The second was that optimal beat synchronization would be determined by the time constant of the 'brain', which surprisingly, was stable across species. 

"Our findings imply that the best tempo for beat synchronization depends on the time constant in the brain. We conducted our investigation with 20 human volunteers and 10 rats. This proves that understanding the perceptual principles of music can benefit from studying the animal brain," Takahashi said.

A beginning to answering one big question and developing the next-generation AI (artificial intelligence)

The team now plan to play genres outside of classical, such as melody and harmony to better understand, how these relate to the dynamics of the brain.

"I am also interested in how, why, and what mechanisms of the brain create human cultural fields such as fine art, music, science, technology and religion,” said Takahashi.

“I believe that this question is the key to understand how the brain works and develop the next-generation AI (artificial intelligence). Also, as an engineer, I am interested in the use of music for a happy life.”