Biological origins of rhythm

Below is an extract from the article with highlighted points about how the brain responds and syncs with rhythm : 

Despite these new findings, Patel and Iversen are not quite ready to let go of the vocal learning hypothesis. “I think it still explains most of the data,” said Iversen, who is now at the Swartz Center for Computational Neuroscience at the University of California, San Diego. They want to see more experiments with other species, in particular dogs and horses, both of which are decidedly not vocal learners. “Some researchers have raised the question: Why don’t dogs dance? After all, dogs have been exposed to our music and dancing for tens of thousand of years,” Iversen said. “It could be intrinsic neural limitations. Maybe you need the right brain circuits.”

If, however, future experiments parallel the latest studies and confirm that an innate sense of rhythm does not depend on neural circuits unique to vocal learners, then how does the brain follow a beat? And what explains the evolutionary origins of this ability? An alternative explanation is coming into focus.

Scientists have known for decades that the brains of all creatures are highly rhythmic biological machines. Both individual neurons and groups of brain cells display repetitive fluctuations in their electrical and chemical activity. But when scientists speak of neural oscillations, they are usually referring to cyclic changes in the strength of the electric fields generated by thousands or millions of interconnected brain cells. Devices such as an electroencephalogram (EEG) — a net of electrodes placed on the scalp — can detect these fluctuations and graph them as sinuous lines similar to those drawn by a seismograph.

Although researchers know that these rhythms vary widely depending on someone’s behavior and that certain rhythms correlate with specific physiological states — wake versus sleep, for instance — their exact purpose remains unclear. Some have argued that they are inevitable and largely ineffectual byproducts of the brain’s wiring. Others think that such vacillations might encode and transmit information. Since at least the 1970s, researchers have proposed that neural oscillations might be especially important for recognizing patterns and rhythms in the environment — that the brain’s own rhythms might actually sync up with those in the world around us. Until recently, however, there was no experimental evidence to support that idea.

In 2005, Large and Joel Snyder, now at the University of Nevada, Las Vegas,published an EEG study showing that when people listen to tones played at regular intervals, certain neural circuits begin to oscillate in time with the tones. It was the first study of its kind. “Oddly, no one had looked before,” Large said. “There had been behavioral evidence accumulating for 40 years, in experiments with people tapping along to beats. But we wanted to go in and see if the brain’s own oscillations sync with what we hear.” Since then, dozens of similar experiments have demonstrated that neural oscillations in both human and other animal brains — including those of monkeys and zebrafish — consistently synchronize with auditory rhythms, including those that come from a simple metronome, classical music or human speech.

Initially, Large and other researchers focused such studies on oscillations in the auditory cortex — a small, centrally located brain region that organizes and interprets neural signals related to sound. In the last eight years, however, studies using magnetoencephalography (MEG) and fMRI — a measurement that tracks blood flow in the brain — have revealed that neural circuits specialized for movement are also used to perceive auditory rhythms. “What was surprising is that motor areas are active even when people are sitting still and just listening,” Large said. “The emerging picture is that the auditory and motor regions sync with each other at the same time as they synchronize to external rhythms, which might help us store and remember the patterns so we can generate them later.”

Patel and Iversen view these findings as further support for the vocal learning hypothesis. The fact that neural oscillations match patterns in speech and music is not sufficient to explain how we or other animals track a beat, they argue. Rather, musical rhythm emerges only in species that have robust bridges between brain areas specialized for hearing and movement, which allows them to synchronize oscillations in those regions all the more precisely. According to their model, when we sit perfectly still and listen to music, brain regions responsible for planning our movements predict when the next beat will drop. It’s as though these regions were anticipating an upcoming footfall while running or the subsequent swing of an arm. The brain’s auditory regions then use the motor regions’ predictions to sync with the beat as well. Put another way, the brain can only make sense of music by relating it to rhythmic bodily movements, even if we aren’t moving at all.

Large thinks this is a misinterpretation. “I don’t think any especially complex circuitry is needed for a sense of rhythm,” he said. “If a brain has connections between the auditory and motor regions, then we should be able to see them synchronize.”

Cook agrees. The first thing to realize, he said, is that what we think of as musical rhythm — singing, dancing or otherwise following an auditory beat — is just one form of rhythm among living things. Consider the synchronous flash of the lustful firefly; or the lockstep of cheetah and gazelle; the ease with which millions of bats move together like living smoke in the night sky; the highly coordinated hunts of wolves and orcas; and the intricate mating dances of tropical birds. Clearly rhythm is fundamental to life — a fact reflected in the numerous links between sensory organs and muscles as well as between sensory and motor regions in all animal brains. Indeed, the fundamental purpose of neurons and brains is to form those connections: to guide behavior using information gathered from the outside world. “You can take this really far back in the evolution of brains,” Cook said. “Brains are basically networks of circuits, and the way they work together is by synchronizing their firing patterns. Rhythm is baked in.”

If rhythm itself is so commonplace among living things, then why is musical rhythm so rare? Perhaps it’s not. What the latest evidence suggests is that the latent ability to follow a beat is much more widespread than previously realized — but, in many species, it probably needs some coaxing to reveal itself. Humans, parrots and elephants are all highly intelligent social species that depend on vocal communication to reproduce and survive. It makes sense that species like these will be especially responsive to auditory rhythms. But their precocious skills necessarily build upon far more common abilities and neural wiring found in a wide range of animals. When these less ostentatious creatures are given appropriate opportunities and encouragement, their latent musical abilities divulge themselves. “The tricky part is motivation,” Cook said. “At first Ronan [the sea lion] didn’t give a crap about the beat. But once we gave her the right training and impetus, she was like, ‘Oh, yeah, of course I can do that.’”

Up until now, the idea has been that biological differences explain humans’ unique musical gifts. Perhaps, though, that discrepancy stems more from culture than biology. Some human infants instinctively bob up and down and shake their limbs when they see people singing and dancing, which implies an innate sense of rhythm. Yet studies show that children do not learn to synchronize their movements to a beat until preschool-age at the earliest, and even then they are not very consistent. And if a child were never exposed to dancing or music, would she develop any musical rhythm at all?

Maybe we’re more like Snowball and Ronan than we’d like to admit: We all have an inborn capacity for rhythm that requires the right environment to reveal itself. Perhaps it’s not that we’re biologically so different or superior, but rather that we’re so much better at creating that suitable environment. Some scholars believe that our hominin ancestors were dancing and singing long before they evolved language, investing considerable resources in ritual performances and the construction of drums and flutes. Today, music continues to suffuse every phase of our lives, from lullaby to elegy. We may not be the only species with rhythm, but we are the only ones with a universal culture of music and dance. We have become the ultimate keepers of the beat.

I find it interesting how the brain's electrical activity synchronises and mimics external rhythms, this is an example of information transfer, rhythmical info from a song is turning into electrical info within the brain and it is finally being turned into visual info through foot tapping or a dance. I feel that a rhythmical stimulus can be used to synchronise the brains and movement of humans, I would like to possibly show this process in a future performance piece of some sort. 

These two videos show how animals can interpret rhythm naturally. I find it interesting how this transfer of information works the same throughout many animals of the animal kingdom.