Perception and the Magic of a Metronome
My patient was struggling. She had injured her knee while skiing and her rehab was going slower than either of us expected. Her perception was that her knee was unstable even though she wasn’t having episodes of instability.
My job as her PT was to not only be her Physical Therapist. I had to become her Perception Transformer. More accurately, I had to facilitate this process.
Human perception is a complex phenomenon. It involves a constant processing of multiple sensory inputs while simultaneously developing our own thoughts and assigned meaning to these, often based on past experiences.
Perception is a critical component to motor control, which I’ll simply define as control of movement. Shumway-Cook describes perception, cognition and action as being the components within an individual that drive motor control. They work together.
The main sensory systems most often referenced when discussing sensorimotor processing are the visual, somatosensory and vestibular systems. To my knowledge we don’t consciously use taste or smell to influence motor control. That leaves us with hearing, also known as audition.
Verbal auditory cues are frequently used to influence motor control but for the purpose of this post I’ll be referring to auditory cues that are nonverbal. For me, non-verbal auditory cues have been an underutilized modality to influence motor control. This changed after I took Chris Johnson’s Clinical Running Essentials course.
“Running is about rhythm and timing” Chris said more than once. He demonstrated how to use a metronome as part of a treadmill assessment to measure, as well as a means to manipulate step rate (cadence). Chris also discussed using a metronome with exercises, like marching drills. During these drills you are slowing down the metronome and this slower speed, according to Chris, helps mitigate threat, acting as graded exposure. Makes sense.
So I started experimenting with the metronome based Run Cadence app on myself and a couple patients, with step rate manipulation and exercises. I was surprised by how quickly individuals were able to adjust.
I was shocked when the patient with the knee injury I mentioned above made a significantly big improvement in her ability to weight bear and control her injured lower extremity with gait and exercises when we added the metronome. I wish I had the pre- and post videos to show you. You’d be surprised too. You might even ask yourself….. Is this magic?
Using a metronome in rehab is not a new thing but it is typically seen more in a “neuro” rehab setting. Research shows the positive effect it has on movement with patients with Parkinson’s or post-stroke. I wasn’t surprised that using the metronome helped. I was surprised by how quickly we were able to see such a significant change.
It got me thinking. What is so special about a metronome? How else could I use this modality?
To make a change of magnitude the stimulus has to be salient. Salience is defined as “the perceptual quality by which an observable thing stands out relative to its environment.” Salience is also required for cortical rewiring to occur, for movement to change, for motor learning.
So how is a beat from a metronome perceived as salient?
Metronome beats help us focus on a simple aspect (rhythmicity) of a complex movement skill (eg. locomotion) The synchronicity of sound and movement is referred to as sensory motor synchronization.
Beats from a metronome are precise and explicit. Our brains don’t need to work very hard to distinguish them from other “noise.” With less competition it is easier to quickly find the pattern.
Another reason we see such a quick change in movements in response to rhythmic auditory cues is they become predictive. After a few beats, the pattern is established and our brains are able to predict the next beat, and the next one, and the next one…
With beat perception the meaning we actively construe is “What’s next?”
Evolutionarily speaking, success at prediction = safety. In his book “Why Zebras Don’t Get Ulcers” Robert Sapolsky talks about the loss of control or predictability as “powerful psychological factors that can trigger a stress-response on their own or make another stressor seem more stressful.” Decreasing threat is essential when optimizing movement.
Using a metronome to slow down movements emphasizes control. The focus is on the beat so there is less interoceptive focus.
Keep in mind that predictive information doesn’t always work, especially if the input is vague. As always, context matters. And it is exactly this, an adjustment of context and assigned meaning, by which perception changes.
Context matters, especially when you are trying to put the pieces of a puzzle together.
I think all the above happened with my patient. I used the metronome with marching drills, step up drills and locomotion training and every time her quality of movement improved. She was able to focus on the predictable beat and felt less threat about putting more weight on her leg. I had her download a metronome app and there was carryover between visits.
Those are the things I could see. There were likely things happening that I couldn’t.
Research shows us that humans are better able to synchronize to auditory cues from a metronome than temporal visual cues. This synchronization of systems is known as entrainment. Multiple studies have now shown that our auditory system is coupled with our motor system. So much so that when we listen to beats without moving areas of our brain that are responsible for movement like the (premotor cortex, basal ganglia and other supplementary motor regions) become active.
In short, you don’t have to be moving to stimulate the motor areas of your brain – that happens when you listen to a beat. Thus, it is no wonder we want to dance or tap our foot or fingers when we here music.
Maybe there is more to it than the onset of timing. Ebonie Rio’s work in Tendon Neuroplastic Training seeks to add a motor control component to the loading management of tendinopathy since cortical inhibition has been shown as a feature of tendinopathy. She found that external pacing (guided by a metronome) with isotonic exercise changed the excitability and inhibition (turning on AND off) of the M1 area of the brain.
If you are interested in this topic you will soon find out that there is a both a plethora and a paucity of research on sensorimotor synchronization and motor control. While reviewing it I'm working on a bunch of N=1's.
Can we use rhythmic auditory cueing to enhance movement and motor control beyond locomotion? Most definitely. We already do it with "neuro" patients, with tempo strength training and speed and agility training. Music is my most consistent training partner. I think there are even more opportunities out there. You just have to listen……
Molinari, M., Leggio, M., De Martin, M. et al, 2003, Neurobiology of Rhythmic Motor Entrainment. Annals of the New York Academy of Sciences, 999, 313-321.
Ross, JM., Balasubramaniam, R., Physical and neural entrainment to rhythm: human sensorimotor coordination across tasks and effector systems. Front Hum Neurosci., 8:576.
Patel A. D., Iversen J. R. (2014). The evolutionary neuroscience of musical beat perception: the Action Simulation for Auditory Prediction (ASAP) hypothesis. Front. Syst. Neurosci. 8:57.
Schaefer, R., 2014, Auditory rhythmic cueing in movement rehabilitation: findings and possible mechanisms. Phil Trans R. Soc. B 369:
Rio, E., Kidgell, D., Moseley, G. L., Gaida, J., Docking, S., Purdam, C., et al. (2016). Tendon neuroplastic training: changing the way we think about tendon rehabilitation: a narrative review. Br. J. Sports Med. 50, 209–215
Why Zebras Don’t Get Ulcers – Robert Sapolsky
Motor Control: Translating Research Into Clinical Practice – Anne Shumway Cook and Marjorie H. Woollacott.