How music helps combat the effects of Parkinson's disease
The beating of our hearts, the flow of air in our lungs, the prosody 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 are isolated: each interacts with its environment, consisting 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 interactions between rhythms. The simple act of walking, step by step, is in fact a complex construction! If this construction breaks down, movement suffers. This raises the question: can we restore rhythm to those who have lost it? Yes, according to some research. Here is a brief explanation, starting with the basics...
While our brain is in control, a whole set of nerve structures governs the associated cycles: networks located in the spinal cord instill the alternating muscle activations necessary for its genesis, but it is the higher brain centers that provide plasticity, since it is at their level that the initiation of movement is planned or the conditions for its proper execution (avoidance of obstacles, etc.) are taken into account.
The basic program originating in the spinal cord networks is thus reshaped according to the demands of the environment, as interpreted 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 possible through the adjustment between auditory/perceived rhythms and motor/executed rhythms. This means that the structures dedicated to perception and those dedicated to movement see their links strengthened, forming a functional network in the brain.
In other words, the brain structures that make us move are also those that make us perceive. When listening to pieces of music, which combine structured sequences of durations, timbres, and accents, the perception of pulsation is the psychological event that occurs most regularly.
When illness derails the machine
Certain conditions can interfere with the production of these rhythms. This is the case with Parkinson's disease, for which difficulty moving is the primary reported disability.
Patients are prone to "freezing of gait, " which is difficulty initiating and continuing walking when approaching an obstacle or turning a corner. These two major movement sequences are affected by the progressive loss of neurons that secrete dopamine, a neurotransmitter, or molecule that transmits information between nerve cells.
A brain structure known as deep, because it is buried beneath the cerebral hemispheres, the basal ganglia (or central gray nuclei), is particularly affected. These structures manage the transition from one stage of a movement to the next: any alteration in their functioning will therefore affect the entire production of rhythmic movements by disrupting the cerebral rhythms necessary for triggering the sub-movements that make up an action.
A choppy gait is symptomatic of this difficulty in transitioning from one sub-movement to another. If a patient with an irregular gait can continue to pedal more smoothly, it is because pedaling is less dependent on the sequential processing of sensory information.
The walking cycle requires the processing of a large amount of sensory information (by the premotor cortex) that takes into account both environmental constraints and the proper execution of the movement in progress: this process is called integration. The correct connection between the cortex and the basal ganglia allows walking to be adapted to the specific features of the environment—anticipating turns, negotiating stairs, crossing streets, etc.
The loss of dopamine neurons inherent in Parkinson's disease prevents these connections from being established (this is referred to as circuitopathy). This manifests itself in a wide range of motor effects, from locomotion to speech.
The effects of music
However, this deficit can be overcome by a simple strategy: simply taking advantage of the brain's appetite for "relevant" rhythms, those with which we can synchronize our movements.
The use of an external clock providing regular cues, such as periodic auditory stimuli, helps compensate for difficulties in initiating and maintaining movement by restoring a temporal structure to actions. This strategy is called " cueing."
Patients benefit from this feedback, whether visual, tactile, or auditory —the latter making it easier to distinguish between the rhythms sent. This is evidenced by an increase in stride length and cadence, as well as a correction in gait asymmetry. Patients walk faster and their increased stability reduces the risk of falling. This improvement reflects better coupling between auditory flow and the musculoskeletal system in the brain. 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 establishment of compensatory mechanisms based on the cortex and cerebellum. Hyperactivation of the cerebellum has been reported in patients performing sensorimotor coordination tasks.
One major factor was highlighted: the accuracy of rhythm perception determines the strength of the coupling between locomotion and music.
Tests have been developed to assess our perception abilities on the one hand, and our ability to synchronize our movements with music on the other. For example, do we notice the discrepancy between a desynchronized metronome and the beat of the music? Are we able to keep time with songs that have more or less obvious rhythms?
The accuracy of perception of the beat and its regularity is representative of coordination abilities and can be compared to established standards. This makes it possible to quantify any impairment and can sometimesaid in diagnosis.
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Possible rehabilitation
There is an apparent contradiction between the beneficial influence of indexing and the deterioration in patient perception.
Concurrent assessment of perceptual abilities and gait under the influence of auditory stimuli clarified this point. Patients who benefit most from cueing are those who have retained their perceptual abilities. This reinforces the hypothesis that the strength of the audio-motor coupling is the primary factor in predicting the benefits of cueing.
However, the consequences of impaired perception are not inevitable. Retraining is possible through serious games in which patients relearn how to synchronize with music, dance (which is a sensorimotor synchronization activity par excellence), etc.
While walking is improved by auditory cues delivered at the right tempo, the interactivity of these stimuli is also an essential factor to consider in order to improve the strength of the coupling.
We have shown that real-time control of the relationship between musical beats and the patient's steps, through continuous adaptation of the musical tempo, ensures ideal audio-motor coupling. Combined with the positive effects of music, both neurochemical (through the release of pleasure hormones) and psychological (through the feeling of escape it provides), the effects of stimulation on walking are immediate. The benefits of indexing are further enhanced.
One of the current challenges is to assess the long-term effects of such an approach.
Medium- and long-term prospects
Full perception of music involves motor structures: don't we need to move our whole body to keep time with a difficult piece of music? The overlap between the structures of our brain that enable us to perceive and those that make us move opens up therapeutic opportunities.
Movement rehabilitation through music strengthens the links between rhythmic auditory perception and motor behavior. Music interferes with 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 dependence 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 II 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, Doctor of Neurology, HDR researcher at the EuroMov Digital Health in Motion unit, University of Montpellier – IMT Mines Ales, University of Montpellier
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