Being able to feel the beat used to be thought of as a trait only found in humans and some primates. Recently, however, more members of the animal kingdom have been taking to the hypothetical dancefloor, keen to prove they can feel the rhythm in their flippers and fur.
The most recent creature to join the dance party is the rat. Researchers have found that rats bop their heads in time to the music. The best tempo for bopping along to was found to be determined by the time constant of the brain. This describes the speed at which nerve cells in the brain can respond to something, and is fairly similar across all species. This may suggest that other species have this ability too.
While some animals can be trained to respond to music, or even generate seemingly a rhythmic noise such as an alarm call, this is not the same as having an innate genetic ability to recognize the beat in a song or even predict what comes next. The ability to do this is known as beat synchronicity.
The team from the University of Tokyo started out with two ideas about whether the rats could feel the beat. One theory was that the ideal music tempo for beat synchronicity would be determined by the time constant of the body (not the brain). This is different for all animals, as it is based on body movement and step frequency, and would therefore be faster for smaller animals, like the rats, compared to humans. The second idea was that the optimal tempo would be determined by the time constant of the brain, which, as mentioned, is surprisingly similar across all species.
To test their theories, human participants wore accelerometers on their headphones, while the rats wore tiny accelerometers directly on their heads that could measure their head bopping abilities. Both humans and rats were then played 60 seconds of Mozart at four different tempos: 75 percent, 100 percent, 200 percent and 400 percent of the original speed.
Mozart’s Sonata for Two Pianos in D Major is normally heard at 132 beats per minute, and the results showed that the rats' head bops were most in time within the 120-140 beats per minute range. The team also discovered that both the people in the experiment and the rats jerked their heads in a similar rhythm, and that the level of head jerking decreased with the increase in the speed of the sonata.
It was found that the head movements were more easily recognized when the rats were in a bipedal position. A second experiment explored this and played songs by popular artists, such as Maroon 5 and Lady Gaga, to the rats.
“Rats displayed innate – that is, without any training or prior exposure to music – beat synchronization most distinctly within 120-140 bpm (beats per minute), to which humans also exhibit the clearest beat synchronization,” explained Associate Professor Hirokazu Takahashi from the Graduate School of Information Science and Technology in a statement.
After conducting the research with human participants and ten rats, the team suggested that “the optimal tempo for beat synchronization depends on time constant in the brain”. They plan to build on this research and look at how this can be compared in humans and other animals, as a means of learning more about the origins of music and dancing.
The paper is published in Science Advances.