An investigation has just shown that moving precisely to the rhythm of music is not an innate ability exclusive to humans, after verifying that rats also have this ability.
The optimal rate of head nodding has been 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 the beat of music may be more widespread across species than previously thought.
This new discovery, presented in Science Advancesoffers not only more information about the animal mind, but also about the origins of our own music and dance.
Apparently, the ability to time our movements to music depends to some extent on our innate genetic ability, and until now this ability was thought to be a uniquely human trait.
Although animals also react to hearing noises, 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 rhythm of a song, respond to it or even predict it, which is known as beat timing.
Relatively recently, research studies (and home videos) have shown that some animals seem to share our drive to move to music. Now, new work by a team at the University of Tokyo, Japan, shows that rats are one of them.
“The rats showed an innate synchronization, that is, without any training or previous exposure to music, of the rhythm most clearly within 120-140 bpm (beats per minute), at which humans also show the clearer rhythm synchronization,” Associate Professor Hirokazu Takahashi of the Graduate School of Information Science and Technology said in a statement.
“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,” he adds.
The expert states that “music exerts a strong attraction on the brain and has profound effects on emotion and cognition.
To use music effectively, we need to reveal the neural mechanism underlying this empirical fact, he says.
I am also a specialist in electrophysiology, which deals with the electrical activity of the brain, and have studied the auditory cortex of rats for many years.”
The team had two alternative hypotheses: The first was that the optimal tempo of music for beat 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 of how fast a rat can move).
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 tempo for beat synchronization depends on the brain’s time constant,” Takahashi said. “This shows that the animal brain can be useful.” to elucidate the perceptual mechanisms of music”.
The rats wore miniature wireless accelerometers, which could measure the slightest movements of the head. The human participants also wore accelerometers in their headphones. Next, one-minute excerpts from Mozart’s Sonata for two pianos in D major, K. 448, were played 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 synchronization was clearest within the 120-140 bpm range. The team also found that both rats and humans shook their heads to a similar beat, and that the level of head shaking decreased the faster the music was sped up.
“To our knowledge, this is the first report of innate rhythm synchronization in animals that was not achieved through musical training or exposure,” Takahashi said.
We also hypothesized that short-term adaptation in the brain was involved in rhythm 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 best rhythm prediction performance occurred when the mean interval between stimuli (the time between the end of one stimulus and the beginning of another) was of about 200 milliseconds (one thousandth of a second),” he stresses. “This was in agreement with the statistics of the intervals between stimuli in classical music, which suggests that the adaptive property in the brain underlies the perception and creation of the music”.
As well as being a fascinating insight into the animal mind and the development of our own rhythmic timing, the 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, are related to brain dynamics. I am also interested in knowing how, why and what mechanisms in the brain create human cultural fields such as fine arts, music, science, technology and religion,” says Takahashi.
“I think this question is the key to understanding how the brain works and developing next-generation AI (artificial intelligence),” he concludes.
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