Music, dance... how the brain and body get into rhythm
On their voyage to the Kerguelen Islands at the beginning of the last century, Raymond Rallier du Baty and his crew landed on Tristan Da Cuhna Island, then populated by castaways whose contact with civilization depended essentially on the wanderings of boats. When one of the adventurers came up with the idea of playing the accordion, the islanders reacted unexpectedly. Deprived of the sound of any musical instrument, they began to dance frenetically in an episode described as a joyous delirium by Rallier du Baty.
Loïc Damm, University of Montpellier and Benoit Bardy, University of Montpellier
This episode reminds us that, more than a cultural element, music is literally inscribed in us. And we still don't know the true extent of its influence.
Music inspires us to move, and we are able to tune our movements to its rhythms - a natural and universal propensity. The most important rhythmic element we identify and base our movements on is the beat. The frequency of the pulse defines the musical tempo.
Tapping, moving to the beat or, of course, dancing may seem trivial activities, but they rely on an essential faculty: coordinating our body movements with regular, predictable auditory rhythms. We speak of a coupling between perception and action.
When it comes to matching your movement to the rhythm of the music, precision of timing is essential. Imagine the choreography of a dancer: you expect the music and movement to be synchronized. In other words, movement frequency and music tempo must converge.
But that's not enough. For their synchronization to be perfect, music and movement must also be in tune with each other: any discrepancy is immediately perceptible. Imagine a musician playing behind his orchestra...
Combining perception and action
To align our movements with musical pulses, we need to perceive rhythm precisely. There's nothing obvious about that: the wealth of rhythmic information in music still fools the best specialized algorithms... And we're not all equal in this respect: our musical training, in particular, affects our perception and synchronization capacities.
Deciphering musical rhythms relies on a vast network of brain structures studied in neuroimaging. Several regions react, and interact, to the presence of a pulse: some usually classified as "sensory" dominant (such as the auditory cortical areas of the brain's temporal lobe), others as "motor" dominant (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 made following an auditory rhythm... as when there is no movement, in a simple perceptual task.
The classic vision of the specialization of brain areas, in this case sensory and motor, therefore tends to disappear when it comes to perceiving a rhythm or moving in response to it.
Movement induced by auditory stimuli is a case of sensory-motor coupling or perception-action. It can be described as the strengthening of connections between distinct brain areas, from those that extract temporal features from auditory information to those that implement movement sequences.
Rhythms everywhere in our bodies
The range of expression of human movement is wider than is commonly recognized, and is rhythmic even in the absence of auditory stimuli. In fact, it extends from voice to walking and running, including virtually all the most creative forms of bodily movement.
Less intuitive, speech production relies on the activation of muscles that make our vocal cords vibrate, giving rise to a rhythmic signature! We become aware of this during a monotonous, soporific speech...
The most obvious rhythmicity remains that of locomotion, probably the most preserved rhythmic physical activity among animals - Homo sapiens included. Walking consists of a simple alternation of left and right steps, through the coordinated activation of our leg muscles.
What's more, the anatomy of our bodies, the length of our bones and the distribution of our masses limit the frequency of our movements, just as the characteristics of a pendulum determine the ticking interval of a clock. In biology, cycles such as walking are maintained over time by a combination of passive (mechanical) and active (muscular) mechanisms.
In order to master this delicate game, 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 networks of neurons (called spinal locomotor networks) capable of producing patterns of muscular activity, i.e. coordinated activation of a set of muscles: such patterns translate into structured movements such as walking.
Our brain, a filter between the body's internal and external rhythms
Our brain also acts as a filter between the rhythms of our body and those of our environment.
Its ability to analyze a musical rhythm and extract its pulse opens up the possibility of using the latter to provide a reference point for our movements, by "injecting" it into the cerebral areas involved.
However, to make their way into our (loco)motor system, external stimuli have to meet certain criteria. Here, mechanics and neurophysiology have their say.
The stability of our own rhythms determines the conditions for locomotor training: a musical tempo can only influence us if it is sufficiently close to our walking cadence. In this case, and provided that there is an interaction between locomotion and music (e.g. of a mechanical or neurophysiological nature), our cadence will converge towards the tempo of the music: we are trained and synchronization occurs.
If we consider the rhythm of our movements, our brain shows a natural affinity for a tempo of around 120 beats per minute. Our walking would be characterized by 70 to 130 steps per minute, for example. In rats, though smaller and walking at a higher rate, it is again auditory stimuli at 120 beats per minute that are most likely to have an influence. The optimal tempo for synchronizing with music could therefore depend on neurobiological constants conserved across species.
Rhythm, a principle of functional brain organization
As early as the 19th 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". That the mechanisms associated with its perception may have been conserved throughout evolution fits in well with the idea that rhythm, just as it is a fundamental aspect of musical construction, would be a principle of functional brain organization.
So, if our species is capable of a unique voluntary predictive synchronization of rhythms, in rodents there already exists a spontaneous synchronization faculty that could constitute an evolutionary precursor, albeit less advanced, but already present. Without this faculty, we wouldn't be able to produce the tunes 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, musical stimuli activate brain regions associated with movement, which in turn contribute to their perception: our ability to analyze musical rhythms is thus reinforced by movement: a coupling between perception and action that enables us to interact more effectively with our environment. And we are even able to extract musical pulses - the basic unit of rhythm - from incoming sounds, so that we can use music to drive our movement by synchronizing ourselves to it.
We're only just beginning to understand how ubiquitous these synchronization phenomena are in our daily lives - when we applaud in unison at the end of a show, or spontaneously synchronize our steps with those of the people around us in a crowd... It's up to science to objectify their influences, as it does for 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. Read theoriginal article.