Precisely moving to a musical beat was considered a skill unique to humans. But now new research shows that even rats have this ability. The optimal pace for nodding along was found to depend on the brain’s time constant (the speed at which our brains can react to something), which is similar across 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 provides further insight into the animal mind, but also into the origins of our own music and dance.
Can you move to the beat, or do you have two left feet? How well we can time our movement to music apparently depends somewhat on our innate genetic ability, and this ability was previously thought to be a uniquely human trait. Although animals also respond to hearing sounds, or can make rhythmic sounds, or are trained to respond to music, this is not the same as the complex neural and motor processes that work together to enable us to naturally recognize beat in a song, respond to it or even predict it. This is called beat synchronicity.
Only relatively recently have research studies (and home videos) shown that some animals seem to share our urge to move to the groove. A new paper from a team at the University of Tokyo provides evidence that rats are one of them.
“Rats exhibited innate — that is, without training or prior exposure to music — beat synchronization most distinctly within 120-140 beats per minute, to which humans also show 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 with our mathematical model of brain adaptation.”
But why play music for rats in the first place? “Music exerts a strong appeal to 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,” says Takahashi. “I’m also a specialist in electrophysiology, which deals with electrical activity in the brain, and I’ve studied the auditory cortex of rats for many years.”
The team had two alternative hypotheses: The first was that the optimal music tempo for beat synchronicity would be determined by the body’s time constant. This is different between species and much faster for small animals compared to humans (think how fast a rat can hover). The second was that the optimal pace would instead be determined by the brain’s time constant, which is surprisingly similar across species.
“After conducting our research with 20 human participants and 10 rats, our results suggest that the optimal pace of beat synchronization depends on the time constant of the brain,” says Takahashi. “This shows that the animal brain can be useful for elucidating the perceptual mechanisms of music.”
The rats were fitted with miniature wireless accelerometers, which could measure the smallest head movements. Human participants also wore accelerometers in headphones. They were then played a one-minute excerpt from Mozart’s Sonata for Two Pianos in D major, K. 448, at four different tempos: seventy-five percent, 100%, 200%, and 400% of the original speed.
The original tempo is 132 bpm and the results showed that the rats’ beat synchronicity was most evident in the range of 120-140 bpm. The team also found that both rats and humans bobbed their heads to the beat in a similar rhythm, and that the level of head bobbing decreased as the music sped up.
“To our knowledge, this is the first report of innate beat synchronization in animals that was not achieved through training or musical exposure,” says Takahashi.
“We also hypothesized that short-term adaptation in the brain was involved in rate tuning in the auditory cortex. We were able to explain this by fitting our neural activity data to a mathematical model of the adaptation. Furthermore, our fitting model showed that in response to random click sequences, the highest prediction performance occurred when the average interstimulus interval (the time between the end of one stimulus and the beginning of another) was about 200 milliseconds (one-thousandth of a second). This matched the statistics for internote intervals in classical music, suggesting that the adaptive nature of the brain underlies the perception and creation of music .”
As well as being a fascinating insight into the animal mind and the evolution of our own beat synchronicity, the researchers also see it as an insight into the creation of music itself.
“Next, I would like to uncover how other musical properties such as melody and harmony relate to brain dynamics. I am also interested in how, why and what mechanisms in the brain create human cultural fields such as art, music, science, technology and religion,” said Takahashi.
“I think this question is the key to understanding how the brain works and developing the next generation of AI (artificial intelligence). Also, as an engineer, I am interested in using music for a happy life.”
“Spontaneous beat synchronization in rats: Neural dynamics and motor entrainment” is published in The progress of science.
Yoshiki Ito et al, Spontaneous beat synchronization in rats: neural dynamics and motor entrainment, The progress of science (2022). DOI: 10.1126/sciadv.abo7019
Provided by the University of Tokyo
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