Greater clinical understanding of motor learning to facilitate sustained change in motor behavior continues to expand the scope of physical therapy interventions and improve outcomes.
A recent research article, “Updates in motor learning: implications for physical therapist practice and education” adds to this body of knowledge by addressing current applications of four well-studied motor learning mechanisms: use-dependent, instructional, reinforcement, and sensorimotor adaptation motor learning.1
(In this article, “mechanism” generally refers to the processes through which motor learning occurs.)
1. Use-dependent motor learning
With use-dependent motor learning, change in motor behavior is driven by repeated practice of specific tasks by the learner. The student must make a motor effort while actively practicing the task. Usage-dependent learning also requires a degree of cognitive engagement in the task, that is, the learner makes intentional changes to his or her movements to solve the movement problem and achieve the goal of the task. Along with task specificity and cognitive engagement, aerobic intensity is another parameter that can be manipulated to optimize use-dependent learning.
Lasting improvements in motor behavior through repeated practice are the result of experience-dependent neuroplasticity or structural and functional changes throughout the central nervous system.2 Extensive task practice results in more automated behaviors and therefore reduces the cognitive load required to complete the task.
A disadvantage of use-dependent motor learning is that achieving long-term improvements in motor behavior may require weeks or months of practice, and generalization of training to real-world progress may be minimal.
2. Instructional motor learning
Instructional motor learning occurs when the physical therapist provides the student with external feedback about a movement error or performance relative to the goal of a task. This knowledge of performance drives the development of an intentional movement strategy to reduce errors on the part of the student. For example, for a person who veers to the left when walking, a therapist might say, “Take bigger steps with your left leg” or “Take longer steps with your left foot.”
With instructional motor learning, the learner can explicitly describe the movement strategy to reduce errors and reproduce it in the future. If the patient can voluntarily produce the desired motor behavior after initial learning, then instructive or strategy-based motor learning was retained.
There is a strong relationship between cognition and instructional motor learning capacity. Therefore, patients with cognitive deficits may not respond as well to this particular motor learning mechanism as their cognitively capable counterparts.
Note: Extensive active practice that drives usage-dependent learning (as described above) will likely also be necessary for the new movement to become automatic or habitual. Additionally, fully developing a new movement habit may require practicing it in multiple contexts that require the learner to employ and generalize the learned movement strategy.
3. Reinforcement motor learning
Reinforcement motor learning is driven by outcome-based feedback or knowledge of outcomes.
Feedback is binary: movement results in success or failure. In this case, the student does No Receive information from the physical therapist on how movement should be modified to achieve success. This non-directional and non-instructive feedback prompts the learner to explore different movements and select actions that have the highest probability of success, while avoiding actions with a low probability of success.3 Reinforcement learning can lead to sustained improvements in motor behavior even in a single session.
For example, the therapist might intentionally position an individual who deviates to the left when walking. The therapist can guide the student in a hallway, with the near wall on the left. The student will try to successfully avoid hitting the wall without the therapist saying anything.
The exact involvement of cognitive processes in motor reinforcement learning is unknown. In theory, due to the variability of an individual’s movement during practice, a successful movement would eventually occur spontaneously. And this would bias the selection of future moves toward a successful or rewarding outcome, even without conscious or cognitive effort.
More recent theories suggest that the intentional exploration of different movements in search of successful behavior may be fundamental to reinforcement learning. Emerging research indicates that motor reinforcement learning may require more cognitive processing than originally proposed.Four. Five
Retention is when the learned movement persists beyond the practice period. Training protocols that require practice of a novel task with reinforcement learning have found better retention than those protocols without reinforced motor learning.6, 7
Interestingly, compared to sensorimotor-based adaptation (discussed below), the improvements seen with reinforcement learning take longer to develop. However, despite the apparent lower learning rate, motor reinforcement learning is associated with longer retention of acquired movements.
4. Motor learning based on sensorimotor adaptation
Motor learning based on sensorimotor adaptation occurs when the actual sensory consequence of a movement differs from the intended sensory consequence of the movement. In other words, the individual encounters an unexpected task demand or a change in the environment that requires modifications in the executed motor program. An example might be walking with a gait device on a gradual downward slope after an initial period of level walking: the proprioceptive feedback from the bottom contact position of the foot with the ground is unexpected. When these errors are detected, the motor command is automatically updated to adapt the movement.
Movements are adjusted repetition by repetition to rapidly reduce sensory prediction errors, allowing movement flexibility in the context of many different task demands. Motor learning based on sensorimotor adaptation occurs rapidly, resulting in a change in motor behavior within minutes. It is currently thought that sensorimotor adaptation occurs automatically, independently of intentional modifications of movements. Therefore, cognition may not be essential for this motor learning mechanism. Surprisingly, sensorimotor adaptation still occurs even when intentional attempts are made to prevent people from correcting their own movement errors.8
Evidence from recent research studies suggests that sensorimotor adaptation occurs alongside instructive or strategy-based motor learning. For example, a recent study found that students, when instructed, could voluntarily demonstrate part of a new walking pattern initially learned through sensorimotor adaptation.9
However, more work is needed to understand how voluntary and involuntary motor learning mechanisms interact to cause an overall change in behavior during walking or other motor tasks.
Implications for physiotherapy
Research now recognizes that there are distinct concurrent motor learning mechanisms that result in sustained changes in movement. With a more complete understanding of motor learning, clinicians can incorporate a greater variety of methods to promote new movement skills.
Currently, physical therapist interventions focus primarily on instructive and use-dependent motor learning. In the future, physical therapists should consider motor reinforcement learning and motor learning based on sensorimotor adaptation as part of our toolbox.
Interventions can be carefully designed to take advantage of any or all of these four motor learning mechanisms. The relative contribution of each of the four motor learning mechanisms can be manipulated by incorporating their unique drivers into movement practice:
- Repeated practice of specific tasks drives use-dependent motor learning.
- Therapist feedback on motor performance will drive instructive (i.e., explicit, strategy-based) motor learning.
- Knowledge of outcome feedback (success/failure) based on external results, without feedback from the therapist, will drive reinforcement motor learning.
- Unexpected task demands or a change in the environment (i.e., perturbations) will drive intrinsic motor learning based on sensorimotor adaptation.
Active engagement in the task remains the essential requirement to promote use-dependent motor learning. But the authors also note that the fundamental understanding of motor learning optimization was established primarily through studies on usage-dependent motor learning and instructional motor learning. Therefore, it is currently unknown to what extent these same principles translate into motor reinforcement learning or motor learning based on sensorimotor adaptation. Consequently, future research is needed to test the effectiveness of these different learning mechanisms for learning a wide range of motor tasks.
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Updates in motor learning: implications for physical therapist practice and education
