Music, dance... How the brain and body get into rhythm
During their voyage to the Kerguelen Islands at the beginning of the last century, Raymond Rallier du Baty and his crew landed on Tristan da Cunha Island, which was then populated by shipwreck survivors whose contact with civilization depended mainly on the misfortune of other ships. When one of the adventurers had the idea of playing the accordion, it provoked unexpected reactions from the islanders. Deprived of the sound of any musical instrument, they began to dance frantically in an episode described as joyful delirium by Rallier du Baty.
Loïc Damm, University of Montpellier and Benoit Bardy, University of Montpellier
This episode reminds us that music is more than just a cultural element; it is literally ingrained in us. And we still don't know the true extent of its influence.
Music encourages us to move, and we are able to synchronize our movements with its rhythms—a natural and universal tendency. The most striking rhythmic element that we identify and use to synchronize our movements is the beat. The frequency of the beat defines the musical tempo.
Tapping, moving to a beat, or dancing are activities that may seem trivial, but they rely on an essential skill: coordinating our body movements with regular, predictable auditory rhythms. This is referred to as the coupling between perception and action.
When it comes to matching your movements to the rhythm of the music, timing is essential. Imagine a dancer's choreography: you expect the music and movement to be synchronized. In other words, the frequency of the movement and the tempo of the music must converge.
But that's not enough. For them to be perfectly synchronized, the music and movement must also be perfectly aligned: any discrepancy is immediately noticeable. Imagine a musician playing behind the rest of the orchestra...
Combining perception and action
To align our movements with musical beats, we need to perceive the rhythm accurately. This is actually not as easy as it sounds: the richness of rhythmic information in music still confounds even the best specialized algorithms... And we are not all equal in this area; our musical training in particular affects our perception and synchronization abilities.
The interpretation of musical rhythms relies on a vast network of brain structures studied in neuroimaging. Several regions react and interact in response to the presence of a beat: some usually classified as predominantly "sensory" (such as the auditory cortical areas of the temporal lobe of the brain), others as predominantly "motor" (such as the basal ganglia or the premotor and motor areas of the frontal lobe). They are involved in both the analysis and perception of rhythm.
But they are also activated when a movement is performed in time with an auditory rhythm...as when there is no movement, in a simple perception task.
The traditional view of the specialization of brain areas, in this case sensory and motor areas, therefore tends to fade when it comes to perceiving a rhythm or moving in response to it.
Movement induced by auditory stimuli is an example of sensorimotor coupling or perception-action. It can be described as the strengthening of connections between distinct areas of the brain, from those that extract temporal characteristics from auditory information to those that implement movement sequences.
Rhythms throughout our body
The range of expressions of human movement is broader than is commonly accepted, and it is rhythmic even in the absence of auditory stimuli. It extends from the voice to walking and running, encompassing virtually all forms of the most creative bodily movements.
Less intuitive, speech production relies on the activation of muscles that vibrate our vocal cords and produce a rhythmic signature! We become aware of this during a monotonous and soporific speech...
The most obvious rhythm is that of locomotion, probably the most widely preserved rhythmic physical activity among animals—including Homo sapiens. Walking consists of a simple alternation of left and right steps, through the coordinated activation of the muscles in our legs.
Furthermore, the anatomy of our bodies, the length of our bones, and the distribution of our mass limit the frequency of our movements, just as the characteristics of a pendulum determine the interval between the ticking of a clock. In biology, cycles, such as walking, are maintained over time by a combination of passive (mechanical) and active (muscular) mechanisms.
To coordinate this delicate movement, proper muscle coordination appears to be an essential function of the entire nervous system. Given the number of muscles involved, simple bipedal locomotion is a fascinating expression of their mastery of rhythms. This is illustrated by the existence, in vertebrates, of neural networks (called spinal locomotor networks) capable of producing patterns of muscle activity, i.e., the coordinated activation of a set of muscles: such patterns result in structured movements such as walking.
Our brain, a filter between rhythms inside and outside the body
Our brain also acts as a filter between our body's rhythms and those of our environment.
Its ability to analyze a musical rhythm and extract its beat opens up the possibility of using the latter to provide a reference point for our movements by "injecting" it into the areas of the brain involved.
However, in order to make their way into our (loco-)motor system, external stimuli must meet certain criteria. And this is where mechanics and neurophysiology come into play.
The stability of our own rhythms determines the conditions for possible locomotor training: a musical tempo can only influence us if it is sufficiently close to our walking pace. In this case, and provided that there is an interaction between locomotion and music (for example, of a mechanical or neurophysiological nature), our cadence will converge with the tempo of the music: we are entrained and synchronization occurs.
If we consider the rhythm of our movements, our brain shows a natural preference for a tempo of around 120 beats per minute. Our walking pace, for example, is characterized by 70 to 130 steps per minute. In rats, which are smaller and walk at a faster pace, auditory stimuli at 120 beats per minute are still the most likely to have an influence. The optimal tempo for synchronizing with music may therefore depend on neurobiological constants that are conserved across species.
Rhythm, a principle of functional organization in the brain
As early as the19th century, naturalist Charles Darwin asserted that "the perception, if not the enjoyment, of musical tempo and rhythm is probably common to all animals, and undoubtedly depends on the common physiological nature of their nervous systems." The fact that the mechanisms associated with its perception may have been preserved throughout evolution fits well with the idea that rhythm, just as it is a fundamental aspect of musical construction, is a principle of functional organization of the brain.
So, while our species is capable of voluntary predictive synchronization unique to rhythms, rodents already have a capacity for spontaneous synchronization that could be considered an evolutionary precursor—less advanced, certainly, but already present. Without this capacity, we would not be able to produce these melodies that speak to us so viscerally.
The combination of neuroscience and movement science has recently led to a better understanding of how the brain functions under the influence of musical stimuli. As we have seen, these stimuli activate areas of the brain associated with movement, which in turn contribute to their perception: our ability to analyze musical rhythms is thus enhanced by movement: a coupling between perception and action that allows us to interact better with our environment. We are even able to extract musical beats, the basic unit of rhythm, from the sounds we hear in order to use music to guide our movements by synchronizing ourselves to it.
We are only beginning to understand the omnipresence of these synchronization phenomena in our daily lives—when we applaud in unison at the end of a show or spontaneously match our pace to that of the people around us in a crowd... It is up to science to objectively assess their influence, as it has done with music... The fields of study relating to social interactions, cognition, and many others are far from exhausted!
Loïc Damm, Postdoctoral Researcher, University of Montpellier and Benoit Bardy, Professor of Movement Sciences, founder of the EuroMov center, member of the Institut Universitaire de France (IUF), University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.