With the Olympics just past and the Paralympics in full swing, it’s difficult not to marvel at every athlete’s mastery of their discipline. Was Andy Murray born to play tennis, or are complex motor patterns something which we all may be capable of achieving? Here, we explore the neuroscience behind motor learning: the process that helps you tie your shoelaces, and allows Andy Murray to hit backhand winners in his sleep.
Neuroscience of schoelaces
Muscle memory (or motor learning) describes the process of committing a specific motor task into memory through repetition. When considering any intricate motor task, the complexity of this process becomes clear. For example, let’s consider what you might perceive to be a relatively ‘simple’ motor task: tying your shoelaces. There are 61 muscles in the hand and forearm alone. Therefore, tying your shoelaces correctly requires the coordinated activity of many muscle groups. Each muscle must contract with a precise amount of force, in precisely the right order, and with an awareness about its position in relation to the shoelaces, and to the other muscles. The nuanced neural control of this process is staggering. And yet most of us are able to tie our shoelaces effortlessly. But it wasn’t always that easy…
Acquisition of muscle memory
When we first conduct a complex motor task, it often feels like a great deal of effort. Large swaths of the brain become activated as we strain to command the muscles required. Two of the most important areas involved in these initial stages of motor learning are the Dorsolateral Premotor Cortex (dPMC) and the Cerebellum. Neuroimaging studies show that these areas are activated independent of the nature of the motor task being learned, and are therefore thought to be the key players in muscle memory. A crude description of the role of each of these areas in motor learning is detailed below:
Neuromotor pathways can be thought of as a hierarchical chain of command. In this model, the dPMC acts as the command centre for motor learning. It is responsible for integrating somatosensory and cognitive inputs, in order to plan motor tasks. Subsequent execution of movement is then initiated by the Primary Motor Cortex.
If the dPMC is the command centre for motor learning, the cerebellum can almost certainly be thought of as its chief adviser. The cerebellum receives input from both the cerebrum and the muscles of the body. It integrates these signals and relays commands to the dPMC to modulate fine motor movements and coordination. The two most important cerebellar cells involved in this process are Purkinje cells and Climbing fibres.
Purkinje cells are perhaps the most visually striking cells in the body. They are comprised of a branched network of roughly 200,000 dendritic spines, giving them more synaptic connections than any other cell in the brain. This allows for an almost infinite medley of synaptic activity. The refinement of this orchestra of activity fine-tunes sensorimotor relationships, and therefore, is key to effective motor learning. Climbing fibres are responsible for inducing this refinement.
Consolidation of motor memory
Climbing Fibres carry sensorimotor signals from the body towards Purkinje cells in the cerebellum. Recent research in mice suggests that Climbing fibres encode the degree of ‘error’ associated with a given motor task . For example, when first learning to touch-type, the learner will be relatively slow, and make errors in their typing accuracy. Climbing fibres register these mistakes, and weaken Purkinje cell synapses that are associated with erroneous motor movements. As the task is repeated, cerebellar signals effectively become ‘de-cluttered’ of erroneous signals. This leads to smooth, replicable motor control. Similar neuroplastic changes have been shown to occur in the cerebrum, following motor learning. For example, a recent study found that the cortical representation of the thumb is significantly enlarged in individuals who use smartphones regularly, compared with a group who do not.
Motor skills: Innate, or learned?
So. With the right practice, can each of us master any motor task we put our minds to? Or are some people born with superior motor abilities?
Evidence for a genetic component of motor memory can be seen across the animal kingdom in courtship and aggression behaviours. Some motor memory appears to be genetically hard-wired in humans, too.
For example, congenitally blind individuals have been shown to share the same facial expressions as sighted individuals, regardless of gender or culture. However, whether some of us are genetically predisposed to more complex motor skills remains unclear. This debate often surfaces when considering elite sportspeople.
Prof. Per-Olof Åstrand, one of the pioneers of exercise physiology, once said:
“A person wishing to become an Olympic champion must be very careful when choosing their parents”
Some athletes are said to be ‘born to play the game’. An unavoidable fact is that we all exist in different shapes and sizes, and that this can be blamed (in part) on our genes. It is also true that different shapes and sizes are more or less suited to any given sport. For example, the average height of an NBA basketball player is 6’7. Superior height is a clear advantage when trying to throw a ball into a 10’ high ring, whilst trying to stop your opponent from doing the same. However, not every 6’7 teenager grows up to play basketball like Michael Jordan. Whilst our bodies may be genetically predisposed to excelling in certain areas, it does not guarantee success.
Unfortunately, genetic variation in the brain is far less clear-cut than measuring someone’s height. Research into the genetic basis of complex motor learning is fairly sparse. We do know that dopaminergic neurotransmission facilitates the neuroplastic changes necessary for motor learning. A recent study even identified five dopamine-related genetic polymorphisms that appear to enhance motor learning. However, it is worth noting that throughout our lives, epigenetic mechanisms alter our gene expression in a non-heritable and individual-specific manner.
Thus, the difficulty that faces scientists is in differentiating between the neurogenetic traits that athletes are born with, versus traits that are acquired. To date, this is something that remains unanswered.
Although we can’t go back in time and test an infant Roger Federer’s brain against his peers, what is clear when analysing interviews with athletes is that it takes a great deal of practice to perform at the top echelons of sport. Federer can often be seen practising even during his matches, by hitting different shots to the ball-kids between points. Tiger Woods is known for continuously tweaking his game. Stephen Hendry often cites a meticulous practice regime as the primary reason for his domination of Snooker in the 1990s.
Sport is riddled with these stories. The muscle movements required to master their disciplines have been honed through years of practice. However, we can be fairly certain that the neuroscientific principles governing motor learning in Federer are the same cellular processes that occurs in us all. Perhaps then, through practice and determination, all of us may be Olympians in-waiting.
See you at Tokyo 2020…