Motor imagery & Action observation
Initially, we used motor imagery (MI) and action observation (AO) as tools to investigate whole-brain activity during the mental simulation of balance tasks using functional magnetic resonance imaging (fMRI). This approach allowed us to examine cortical and subcortical brain activation under stable, non-moving conditions – something that is difficult to achieve with other neuroimaging methods during the simulation of complex motor tasks. We demonstrated that mentally simulating challenging balance tasks activates the relevant motor brain regions, with activation patterns varying according to the postural demands of the task [1]. Furthermore, we identified age-related differences in brain activation, particularly increased activity in cortical areas in older adults, a phenomenon commonly referred to as cortical overactivation [2]. Interestingly, we subsequently showed that several weeks of balance training reduced these cortical overactivations, resulting in brain activation patterns in older adults that more closely resembled those of young, healthy adults during the mental simulation of balance tasks [3].
Beyond their value as neuroscientific tools, we also demonstrated that the mental simulation of balance tasks can improve actual motor performance. Specifically, we showed for the first time that practicing balance tasks through motor imagery and action observation, without physically performing the tasks, can improve dynamic balance control in young adults [4]. These findings changed our perspective on MI and AO: they are not merely methods for investigating brain function in a stable, non-moving condition, but can also engage and potentially train the motor system in ways that resemble actual movement execution. This is in line with Jeannerod's influential hypothesis that "the motor system is part of a simulation network that is activated under a variety of conditions in relation to action, either self-intended or observed from other individuals" [5].
To better understand how mental simulation engages the motor system, we subsequently used transcranial magnetic stimulation (TMS) to investigate the activation of distinct fast and slower corticospinal motor pathways during motor imagery. Remarkably, the activation pattern during motor imagery closely resembled that observed during actual muscle contractions. These findings demonstrated that motor imagery produces task- and pathway-specific subliminal activation of distinct neuronal populations within the primary motor cortex [6].
From basic neuroscience to clinical applications
We have also explored the therapeutic potential of mental simulation in different patient populations. In patients with chronic neck pain, we demonstrated that motor imagery and action observation can improve impaired cervical joint position sense[7]. In a single-case fMRI study involving a patient with chronic neck pain, we further showed that mentally simulating pain-inducing movements activated brain regions associated with pain processing (the so-called pain matrix). Interestingly, directing the patient's attention towards a distracting task prevented this activation, suggesting that attentional processes can modulate the brain's response to the mental simulation of painful movements [8].
Perhaps most importantly from a clinical perspective, we demonstrated that adding mental simulation of locomotor tasks to standard rehabilitation can accelerate functional recovery in older adults following total hip arthroplasty [9]. Together, these findings highlight the potential of MI and AO as accessible, non-invasive approaches to complement conventional motor training and rehabilitation, particularly when physical practice is difficult, limited, or not yet possible.
Exploring the limits of mental simulation
Although our previous findings clearly demonstrate that mental simulation can engage and, under certain conditions, train the motor system, we are currently pursuing a complementary research direction: exploring the limits of mental simulation. In particular, we are investigating whether motor imagery can also improve explosive (ballistic) movements, which require motoneurons to rapidly increase their discharge rates to generate force within a very short time. Our current hypothesis is that mental simulation alone may be insufficient to induce the neural adaptations required for such rapid force production, as these adaptations may depend on actual descending neural drive reaching the spinal motoneuron pool.
Building on this idea, we have investigated whether combining motor imagery of explosive contractions with actual descending neural activation induced by magnetic stimulation of the primary motor cortex can overcome these limitations and improve motor performance. This is actually true. However, the final control experiments are currently underway, and we look forward to sharing these findings in the near future.
Overall, our research aims to better understand how the brain represents, simulates, and controls movement – and how these mechanisms can be harnessed to improve motor performance, motor learning, and rehabilitation.
1. Taube, W., M. Mouthon, C. Leukel, H.M. Hoogewoud, J.M. Annoni, and M. Keller, Brain activity during observation and motor imagery of different balance tasks: An fMRI study. Cortex, 2015. 64: p. 102-114..
2. Mouthon, A., J. Ruffieux, M. Mouthon, H.M. Hoogewoud, J.M. Annoni, and W. Taube, Age-Related Differences in Cortical and Subcortical Activities during Observation and Motor Imagery of Dynamic Postural Tasks: An fMRI Study. Neural Plasticity, 2018. 2018.
3. Ruffieux, J., A. Mouthon, M. Keller, M. Mouthon, J.M. Annoni, and W. Taube, Balance Training Reduces Brain Activity during Motor Simulation of a Challenging Balance Task in Older Adults: An fMRI Study. Frontiers in Behavioral Neuroscience, 2018. 12.
4. Taube, W., M. Lorch, S. Zeiter, and M. Keller, Non-physical practice improves task performance in an unstable, perturbed environment: motor imagery and observational balance training. Frontiers in Human Neuroscience, 2014. 8.
5. Jeannerod, M., Neural simulation of action: a unifying mechanism for motor cognition. Neuroimage., 2001. 14(1 Pt 2): p. S103-S109.
6. Keller, M., W. Taube, and B. Lauber, Task-dependent activation of distinct fast and slow(er) motor pathways during motor imagery. Brain Stimulation, 2018. 11(4): p. 782-788.
7. Beinert, K., S. Preiss, M. Huber, and W. Taube, Cervical joint position sense in neck pain. Immediate effects of muscle vibration versus mental training interventions: a RCT. Eur J Phys Rehabil Med, 2015. 51(6): p. 825-32.
8. Beinert, K., A. Mouthon, M. Keller, M. Mouthon, J.M. Annoni, and W. Taube, Neural Correlates of Maladaptive Pain Behavior in Chronic Neck Pain - A Single Case Control fMRI Study. Pain Physician, 2017. 20(1): p. E115-E125.
9. Marusic, U., S. Grosprêtre, A. Paravlic, S. Kovac, R. Pisot, and W. Taube, Motor Imagery during Action Observation of Locomotor Tasks Improves Rehabilitation Outcome in Older Adults after Total Hip Arthroplasty. Neural Plasticity, 2018. 2018.