Accurately transitioning to a musical beat was thought to be an ability inherently unique to humans. However, new research now shows that rats also have this ability. The optimal rate for nodding along was found to depend on the time constant in the brain (the speed at which our brain can respond 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 across species than previously thought. This new discovery offers not only further insight into the animal mind, but also into the origins of our own music and dance.
Can you keep up with the beat or do you have two left feet? Apparently, how well we can time our movement to music depends somewhat on our innate genetic ability, and this ability was previously thought to be a uniquely human trait. While animals also respond to hearing 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 the beat in a song . respond to it or even anticipate it. This is referred to as beat synchronicity.
Only relatively recently, research studies (and home videos) have shown that some animals seem to share our urge to move into the groove. A new paper by a team at the University of Tokyo provides evidence that rats are one of them.
“Rats that appear innate – that is, without any training or prior exposure to music – beat sync most distinctly within 120-140 bpm (beats per minute), at which humans also show the clearest beat sync,” explained associate professor Hirokazu Takahashi from the Graduate School of Information Science and Technology;
“The auditory cortex, the area 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 powerful 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 event,” Takahashi said. “I’m also an expert in electrophysiology, which deals with electrical activity in the brain, and I’ve been studying the auditory cortex of rats for many years.”
The team had two alternative hypotheses: The first was that the optimal music tempo for rhythm synchronization 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 it can kill a rat). The second was that the optimal rate would 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 rate for pulse synchronization depends on the time constant in the brain,” Takahashi said. “This shows that the animal brain can be useful for elucidating the perceptual mechanisms of music.”
The rats were fitted with wireless, tiny accelerometers that could measure the slightest head movements. The people who participated also wore accelerometers in the headphones. One-minute excerpts from Mozart’s Sonata for Two Pianos in D major, K. 448, were then played at four different tempos: seventy-five percent, 100%, 200%, and 400% of the original speed.
The initial rate is 132 bpm and the results showed that the timing of the rats’ pulses was clearer within the range of 120-140 bpm. The team also found that both rats and humans bobbed their heads to the beat at a similar rate, and that the level of head bobbing decreased as the music sped up.
“To our knowledge, this is the first report of innate heart rate synchronization in animals that was not achieved through training or musical exposure,” Takahashi said.
“We also hypothesized that short-term adaptation in the brain is involved in pulse tuning in the auditory cortex. We were able to explain this by fitting our neural activity data to a mathematical model of adaptation. Furthermore, our adaptation model showed that in response to sequences of random clicks, the highest rate prediction performance occurred when the average interstimulus interval (the time between the end of one stimulus and the start of another) was about 200 milliseconds (one millisecond). This matched the statistical of intermediate intervals in classical music, suggesting that the adaptive property of the brain underlies the perception and creation of music.”
As well as a fascinating insight into the animal mind and the development of our own rhythmic 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. science, technology and religion,” Takahashi said.
“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’m interested in using music for a happy life.”
“Spontaneous pulse synchronization in rats: Neural dynamics and motor entrainment” is published in Advances in Science.
Yoshiki Ito et al, Spontaneous pulse synchronization in rats: Neural dynamics and motor entrainment, Advances in Science (2022). DOI: 10.1126/sciadv.abo7019
Provided by the University of Tokyo
Reference: Rats bopping in video demonstrate innate beat synchronization in animals for first time (2022, November 11) Retrieved November 11, 2022, from https://phys.org/news/2022-11-rats-bopping -video-innate-synchronization.html
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