Moving with precision to a musical beat was considered a skill inherently unique to humans. However, new research now shows that rats have this ability too. The optimal rhythm for nodding depended on the time constant in the brain (the speed at which our brain can respond to something), which is similar for all species.
This means that the ability of our auditory and motor systems to interact and move to music may be more widespread among species than previously thought. This new discovery not only offers deeper insight into the animal spirit, but also into the origins of our own music and dance.
Can you move in rhythm or do you have two left feet? Apparently, how we can time our movement to music is somewhat dependent on our innate genetic ability, and this skill was previously thought to be a uniquely human trait. Although animals also respond to auditory noise, or may make rhythmic sounds, or be trained to respond to music, this is not the same as the complex neural and motor processes that work together to allow us to naturally recognize rhythm of a song, responding to it or even predicting it. This is called beat synchronicity.
It’s only relatively recently that research studies (and home videos) have shown that some animals seem to share our urge to move in the groove. A new paper from a team at the University of Tokyo provides evidence that rats are one of them.
“Rats display innate synchronization – that is, without any prior training or exposure to music – the synchronization of beats most distinctly between 120 and 140 bpm (beats per minute), with which humans also exhibit the clearest beat synchronization,” explained Associate Professor Hirokazu Takahashi of the Graduate School of Information Science and Technology.
“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.”
But why play music to rats in the first place? “Music exerts a strong pull on the brain and has profound effects on emotion and cognition. To use music effectively, we need to uncover the neural mechanism underlying this empirical fact,” Takahashi said. “I am also a specialist in electrophysiology, which is interested in electrical activity in the brain, and have been studying the auditory cortex of rats for many years.”
The team had two alternative hypotheses: the first was that the optimal musical tempo for beat synchronicity would be determined by the time constant of the body. This is different between species and much faster for small animals compared to humans (think how quickly a rat can scuttle). The second was that the optimal tempo would instead be determined by the time constant of the brain, which is surprisingly similar across species.
“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,” Takahashi said. “This demonstrates that the animal brain can be useful in elucidating the perceptual mechanisms of music.”
The rats were equipped with miniature wireless accelerometers capable of measuring the slightest movements of the head. The human participants also wore accelerometers on headphones. They were then played one-minute excerpts from Mozart’s Sonata for Two Pianos in D Major, K. 448, at four different tempos: seventy-five percent, 100 percent, 200 percent, and 400 percent of the speed. ‘origin.
The original tempo is 132 bpm and the results showed that the rats’ beat synchronicity was clearest in the 120-140 bpm range. The team also found that rats and humans shook their heads in time with the beat at a similar rate, and that the level of head shaking decreased as the music was sped up.
“To the best of our knowledge, this is the first report of innate beat synchronization in animals that has not been achieved by training or musical exposure,” Takahashi said.
“We also hypothesized that short-term adaptation in the brain was involved in beat tuning in the auditory cortex. We were able to explain this by fitting our neural activity data to a mathematical model of adaptation. Additionally, our adaptation model showed that in response to random click sequences, the highest beat prediction performance occurred when the average interstimulus interval (the time between the end of a stimulus and the start of another) was about 200 milliseconds (one thousandth of a second). This matched the statistics of internote intervals in classical music, suggesting that the adaptive property in the brain underlies the perception and creation of music.”
As well as being a fascinating insight into the animal spirit and the development of our own rhythmic synchronicity, researchers also see it as insight into the creation of music itself.
“Next, I would like to reveal how other musical properties such as melody and harmony relate to brain dynamics. I am also interested in how, why, and what brain mechanisms create human cultural fields such as fine arts, music, science, technology and religion,” Takahashi said.
“I believe this question is the key to understanding how the brain operates and develops next-generation AI (artificial intelligence). Moreover, as an engineer, I am interested in the use of music for a happy life.”
“Spontaneous synchronization of beats in the rat: neural dynamics and motor drive” is published in Scientists progress.
Yoshiki Ito et al, Spontaneous beat synchronization in the rat: neural dynamics and motor drive, Scientists progress (2022). DOI: 10.1126/sciadv.abo7019
University of Tokyo
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