How music helps combat the effects of Parkinson's disease
The beating of our hearts, the flow of air through our lungs, the rhythm of our voices, or the movements of our legs… Our bodies are a sea of different rhythms. None of the biological systems that generate them operate in isolation: each interacts with its environment, which consists of other systems inside or outside our bodies that have their own rhythms.
Loïc Damm, University of Montpellier; Benoît Bardy, University of Montpellier and Valérie Cochen de Cock, University of Montpellier
Movement is a fine example of the interplay between rhythms. The simple act of walking, step by step, is in fact a complex process! If this process breaks down, movement suffers as a result. This raises the question: can we restore rhythm to those who have lost it? Yes, some research suggests. Here’s a brief explanation, starting with the basics…
While our brain is in control, a whole set of neural structures governs the associated cycles: networks located in the spinal cord trigger the alternating muscle contractions necessary for its generation, but it is the higher brain centers that provide the flexibility, since it is at this level that the initiation of movement is planned or the conditions for its proper execution are taken into account (avoidance of obstacles, etc.).
The basic program originating in the spinal cord networks is thus adapted to the demands of the environment, as conveyed by our senses… This is what neuroscientists call “perception-action coupling ”: because it controls our muscles and integrates auditory and visual information, the nervous system is able to link our senses to our behaviors.
This is what happens when we play music in a group, where the temporal coordination of our movements with those of our partners allows us to be in unison. This synchronization is made possible by the alignment between auditory/perceived rhythms and motor/executed rhythms. This means that the connections between the brain structures primarily dedicated to perception and those primarily dedicated to movement are strengthened, forming a functional network in the brain.
In other words, the brain structures that control our movements are also the ones that enable us to perceive. When listening to pieces of music—which combine structured sequences of duration, timbre, and accent—the perception of the beat is the psychological phenomenon that occurs most frequently.
When illness throws a wrench in the works
Certain medical conditions can interfere with the production of these rhythms. This is the case with Parkinson’s disease, in which difficulty moving is the most commonly reported disability.
Patients experience "freezing of gait, " which refers to difficulty initiating and maintaining movement when approaching an obstacle or a turn. These two major phases of movement are affected by the progressive loss of neurons that secrete “dopamine”—a neurotransmitter, or a molecule that facilitates the transmission of information between nerve cells.
A brain structure known as the basal ganglia (or central gray nuclei)—so called because it lies deep within the cerebral hemispheres—is particularly affected. These structures manage the transition from one phase of a movement to the next: any impairment in their functioning will therefore affect the entire production of rhythmic movements by disrupting the brain rhythms necessary to trigger the sub-movements that make up an action.
A choppy gait is indicative of this difficulty in transitioning from one sub-movement to the next. If a patient with an irregular gait can still pedal more smoothly, it is because pedaling relies less on the sequential processing of sensory information.
The gait cycle requires the premotor cortex to process a great deal of sensory information that accounts for both environmental constraints and the proper execution of the current movement; this process is known as integration. The proper connection between the cortex and the basal ganglia allows walking to adapt to the specific features of the environment—such as anticipating a turn, navigating stairs, or crossing a street…
The loss of dopamine-producing neurons characteristic of Parkinson’s disease prevents these connections from forming (a condition known as circuitopathy). This manifests as a wide range of motor symptoms, from movement to speech.
The Effects of Music
Yet this shortcoming can be overcome with a simple strategy: by simply taking advantage of the brain’s preference for “relevant” rhythms—those with which we can synchronize our movements.
Using an external timer that provides regular cues, such as periodic auditory stimuli, helps compensate for difficulties in initiating and sustaining movement by restoring a temporal structure to actions. This strategy is called “cueing.”
Patients benefit from this cueing, whether visual, tactile, or auditory —the latter making it easier to distinguish the rhythms being provided. This is evidenced by an increase in step frequency and stride length, as well as a correction of gait asymmetries. The patient walks faster, and their increased stability reduces the risk of falling. This improvement reflects better coordination between auditory input and the musculoskeletal system at the brain level. These benefits extend beyond the music-assisted walking sessions.
There are two possible explanations (which are not mutually exclusive) for these improvements:
- residual activation of the basal ganglia,
- the development of compensatory mechanisms involving the cortex and the cerebellum. In fact, hyperactivation of the cerebellum has been reported in patients during sensorimotor coordination tasks.
One key finding has been highlighted: the accuracy of rhythm perception determines the strength of the link between movement and music.
Tests have been developed to assess, on the one hand, our perceptual abilities and, on the other hand, our ability to synchronize our movements with music. For example, do we notice the discrepancy between an out-of-sync metronome and the beats of the music? Are we able to tap along to songs with rhythms that are more or less obvious?
The accuracy of perceiving the heartbeat and its regularity reflects a person’s coordination skills and can be compared to established standards. This makes it possible to quantify any impairment and can sometimesaid in diagnosis.
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Rehabilitation is possible
There appears to be a contradiction between the beneficial effects of indexing and the deterioration in patients’ perception.
A concurrent assessment of perceptual abilities and gait under the influence of auditory stimuli helped clarify this point. The patients who benefit most from cueing are those who have retained their perceptual abilities. This supports the hypothesis that the strength of the auditory-motor coupling is the primary factor in predicting the benefits of cueing.
However, the consequences of impaired perception are not inevitable. Rehabilitation is possible through serious games in which patients relearn how to synchronize with music, dance— which is the ultimate sensorimotor synchronization activity—and so on.
While walking is enhanced by auditory cues delivered at the right tempo, the interactivity of these cues is also a key factor to consider in improving the strength of the coupling.
We have demonstrated that real-time control of the relationship between musical beats and the patient’s steps—achieved through continuous adjustment of the musical tempo—ensures optimal audio-motor synchronization. Combined with the positive effects of music—neurochemical, through the release of “feel-good” hormones, and psychological, through the sense of escapism it provides—the effects of this stimulation on walking are immediate. The benefits of gait training are further enhanced as a result.
One of the current challenges is to assess the long-term effects of such an approach.
Medium- and long-term outlook
A full appreciation of music involves motor functions: don’t we need to move our whole body to keep time with a difficult piece? The overlap between the parts of our brain that enable us to perceive and those that enable us to move opens up therapeutic possibilities.
Music-based movement rehabilitation effectively strengthens the links between rhythmic auditory perception and motor behavior. Music influences the brain’s motor networks and can compensate for certain deficits caused by Parkinson’s disease. This approach can help improve patients’ quality of life and reduce their reliance on medication. It is therefore a powerful rehabilitation tool that complements pharmacological therapy.
Other conditions involving motor deficits are also being studied. Multiple sclerosis, post-stroke conditions, and type 2 diabetes are currently being investigated by our team.
Loïc Damm, Postdoctoral Researcher, University of Montpellier; Benoît Bardy, Professor of Movement Sciences, founder of the EuroMov center, member of the Institut Universitaire de France (IUF), University of Montpellier and Valérie Cochen de Cock, PhD in Neurology, HDR researcher at the EuroMov Digital Health in Motion unit, University of Montpellier – IMT Mines Ales, University of Montpellier
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