The relationship between corticospinal excitability during motor imagery and motor imagery ability

Motor imagery from brain to muscle: a commentary on Bach et al., (2022)

In a recent article entitled "Why motor imagery is not really motoric: towards a re-conceptualization in terms of effect-based action control", Bach et al. nicely renewed the concept of motor equivalence between actual movement and motor imagery (MI), i.e. the mental simulation of an action without its corresponding motor output. Their approach is largely based on behavioral studies and, to a lesser extent, on the literature using cerebral imagery. However, the literature on cortico-spinal circuitry modulation during MI can provide further, interesting aspects. Indeed, when it comes to addressing the motor system, one should consider the whole path from brain region to muscle contraction, including sub-cortical structures such as the spinal circuitry. This commentary aims at bridging this gap by providing supplemental evidence and outlining a complementary approach.

Changes in corticospinal excitability during motor imagery by physical practice of a force production task: Effect of the rate of force development during practice

Transcranial magnetic stimulation studies have indicated that the physical practice of a force production task increases corticospinal excitability during motor imagery (MI) of that task. However, it is unclear whether this practice-induced facilitation of corticospinal excitability during MI depends on a repeatedly practiced rate of force development (RFD). We aimed to investigate whether corticospinal excitability during MI of an isometric force production task is facilitated only when imagining the motor task with the same RFD as the physically practiced RFD. Furthermore, we aimed to examine whether corticospinal excitability during MI only occurs immediately after physical practice or is maintained. Twenty-eight right-handed young adults practiced isometric ramp force production using right index finger abduction. Half of the participants (high group) practiced the force production with high RFD, and the other half (low group) practiced the force production with low RFD. Questionnaire scores indicating MI ability were similar in the two groups. We examined the force error relative to the target force during the force production task without visual feedback, and motor evoked potential (MEP) amplitudes of the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles during the MI of the force production task under practiced and unpracticed RFD conditions before, immediately after, and 20 min after physical practice. Our results demonstrated that the force error in both RFD conditions significantly decreased immediately after physical practice, irrespective of the RFD condition practiced. In the high group, the MEP amplitude of the FDI muscle during MI in the high RFD condition significantly increased immediately after practice compared to that before, whereas the MEP amplitude 20 min after practice was not significantly different from that before practice. Conversely, the MEP amplitude during MI in the high RFD condition did not change significantly in the low group, and neither group had significant changes in MEP amplitude during MI in the low RFD condition. The facilitatory effect of corticospinal excitability during MI with high RFD observed only immediately after physical practice in the high RFD condition may reflect short-term functional changes in the primary motor cortex induced by physical practice.

Tactile versus motor imagery: differences in corticospinal excitability assessed with single-pulse TMS

Tactile Imagery (TI) remains a fairly understudied phenomenon despite growing attention to this topic in recent years. Here, we investigated the effects of TI on corticospinal excitability by measuring motor evoked potentials (MEPs) induced by single-pulse transcranial magnetic stimulation (TMS). The effects of TI were compared with those of tactile stimulation (TS) and kinesthetic motor imagery (kMI). Twenty-two participants performed three tasks in randomly assigned order: imagine finger tapping (kMI); experience vibratory sensations in the middle finger (TS); and mentally reproduce the sensation of vibration (TI). MEPs increased during both kMI and TI, with a stronger increase for kMI. No statistically significant change in MEP was observed during TS. The demonstrated differential effects of kMI, TI and TS on corticospinal excitability have practical implications for devising the imagery-based and TS-based brain-computer interfaces (BCIs), particularly the ones intended to improve neurorehabilitation by evoking plasticity changes in sensorimotor circuitry.

Observing an expert's action swapped with an observer's face increases corticospinal excitability during combined action observation and motor imagery

This study aimed to examine whether observing an expert's action swapped with an observer's face increases corticospinal excitability during combined action observation and motor imagery (AOMI). Twelve young males performed motor imagery of motor tasks with different difficulties while observing the actions of an expert performer and an expert performer with a swapped face. Motor tasks included bilateral wrist dorsiflexion (EASY) and unilateral two-ball rotating motions (DIFF). During the AOMI of EASY and DIFF, single-pulse transcranial magnetic stimulation was delivered to the left primary motor cortex, and motor-evoked potentials (MEPs) were obtained from the extensor carpi ulnaris and first dorsal interosseous muscles of the right upper limb, respectively. Visual analogue scale (VAS) assessed the subjective similarity of the expert performer with the swapped face in the EASY and DIFF to the participants themselves. The MEP amplitude in DIFF was larger in the observation of the expert performer with the swapped face than that of the expert performer (P = 0.012); however, the corresponding difference was not observed in EASY (P = 1.000). The relative change in the MEP amplitude from observing the action of the expert performer to that of the expert performer with the swapped face was positively correlated with VAS only in DIFF (r = 0.644, P = 0.024). These results indicate that observing the action of an expert performer with the observer's face enhances corticospinal excitability during AOMI, depending on the task difficulty and subjective similarity between the expert performer being observed and the observer.

Modulation of lower limb muscle corticospinal excitability during various types of motor imagery

Motor imagery (MI) is used for rehabilitation and sports training. Previous studies focusing on the upper limb have investigated the effects of MI on corticospinal excitability in the muscles involved in the imagined movement (i.e., the agonist muscles). The present study focused on several lower-limb movements and investigated the influences of MI on corticospinal excitability in the lower limb muscles. Twelve healthy individuals (ten male and two female individuals) participated in this study. Motor-evoked potentials (MEP) from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and soleus (SOL) muscles were elicited through transcranial magnetic stimulation (TMS) to the primary motor cortex during MI of knee extension, knee flexion, ankle dorsiflexion, and ankle plantarflexion and at rest. The results showed that the RF MEPs were significantly increased during MI in knee extension, ankle dorsiflexion, and ankle plantarflexion but not in knee flexion, compared with those at rest. The TA MEPs were significantly increased during MI in knee extension and foot dorsiflexion, while MEPs were not significantly different during MI in knee flexion and foot dorsiflexion than those at rest. For the BF and SOL muscles, there was no significant MEP modulation in either MI. These results demonstrated that corticospinal excitability of the RF and TA muscles was facilitated during MI of movements in which they are active and during MI of lower-limb movements in which they are not involved. On the contrary, corticospinal excitability of the BF and SOL muscles was not facilitated by MI of lower-limb movements. These results suggest that facilitation of corticospinal excitability depends on the muscle and the type of lower-limb MI.

The Influence of Resistance Training Experience on the Efficacy of Motor Imagery for Acutely Increasing Corticospinal Excitability

Both motor imagery and resistance-training enhance motor function and corticospinal excitability. We tested the hypothesis that young participants with significant resistance-training experience would show heightened corticospinal excitability during a single session of motor imagery training. Fifty-six participants (mean ± SD age = 22 ± 2 years) were divided into resistance-trained and untrained groups. Forty-one upper-body resistance trained (21 males, 20 females; mean ± SD relative one repetition maximum bench press = 0.922 ± 0.317 kg/kg) and 15 untrained (4 males, 11 females; mean ± SD relative one repetition maximum bench press = 0.566 ± 0.175 kg/kg) participants visited the laboratory on three separate occasions. The first visit served as the familiarization session. During visits 2 and 3, participants engaged in a hand/wrist motor imagery protocol or rested quietly (control condition) in a randomized order. Before and after the interventions, single-pulse transcranial magnetic stimulation (TMS) over the motor cortex was used to measure resting motor-evoked potential amplitude of the first dorsal interosseous muscle. Our main finding was that motor imagery acutely increased corticospinal excitability by ~64% (marginal means pre = 784.1 µV, post = 1246.6 µV; p < 0.001, d = 0.487). However, there was no evidence that the increase in corticospinal excitability was influenced by resistance-training experience. We suspect that our results may have been influenced by the specific nature of the motor imagery task. Our findings have important implications for motor imagery prescription and suggest that motor imagery training may be equally beneficial for both resistance-trained and untrained populations. This study was prospectively registered at ClinicalTrials.gov (Identifier: NCT03889548).

Corticospinal excitability changes during muscle relaxation and contraction in motor imagery

To enhance smooth muscle contraction and relaxation during rehabilitation and sports activities, a comprehensive understanding of the motor control mechanisms within the central nervous system is necessary. However, current knowledge on these aspects is insufficient. Therefore, this study aimed to deepen our understanding of motor controls, by investigating the alterations in corticospinal excitability within cortical motor areas related to muscle contraction and relaxation using motor imagery with a reaction time task paradigm. Transcranial magnetic stimulation was used to measure the motor-evoked potentials in the first dorsal interosseous muscle of the right hand after the 'go' signal. Static weak muscle contraction (Experiment 1: 18 healthy participants) and resting state (Experiment 2: 16 healthy participants) were applied as background factors, and a trial without motor imagery was performed as a control. Muscle contraction was maintained in the background in the contraction motor imagery. A decrease in excitability in the relaxation motor imagery task occurred compared with the control. When the muscles were at rest, an increase in excitability in the contraction motor imagery and a transient increase in excitability in the relaxation motor imagery occurred compared with the control condition. Hence, the excitability of contraction and relaxation motor imagery is characterized by a continuous increase in excitability, transient increase and subsequent decrease in excitability, respectively. These results suggest that muscle contraction sensory information in the background condition may be necessary for muscle relaxation. Matching the background conditions may be crucial when utilizing motor imagery for rehabilitation or sports training.

Implicit Sensorimotor Adaptation Proceeds in Absence of Movement Execution

In implicit sensorimotor adaptation, a mismatch between the predicted and actual sensory feedback results in a sensory prediction error (SPE). Sensory predictions have long been thought to be linked to descending motor commands, implying a necessary contribution of movement execution to adaptation. However, recent work has shown that mere motor imagery (MI) also engages predictive mechanisms, opening up the possibility that MI might be sufficient to drive implicit adaptation. In a within-subject design in humans (n = 30), implicit adaptation was assessed in a center-out reaching task, following a single exposure to a visuomotor rotation. It was hypothesized that performing MI of a reaching movement while being provided with an animation of rotated visual feedback (MI condition) would lead to postrotation biases (PRBs) similar to those observed when the movement is executed (Execution condition). Results revealed that both the MI and Execution conditions led to significant directional biases following rotated trials. Yet the magnitude of these biases was significantly larger in the Execution condition. To further probe the contribution of MI to adaptation, a Control condition was conducted in which participants were presented with the same rotated visual animation as in the MI condition, but in which they were prevented from performing MI. Surprisingly, significant biases were also observed in the Control condition, suggesting that MI per se may not have accounted for adaptation. Overall, these results suggest that implicit adaptation can be partially supported by processes other than those that strictly pertain to generating motor commands, although movement execution does potentiate it.

A Quantitative Investigation of Mental Fatigue Elicited during Motor Imagery Practice: Selective Effects on Maximal Force Performance and Imagery Ability

In the present study, we examined the development of mental fatigue during the kinesthetic motor imagery (MI) of isometric force contractions performed with the dominant upper limb. Participants (n = 24) underwent four blocks of 20 MI trials of isometric contractions at 20% of the maximal voluntary contraction threshold (20% MVC_MI) and 20 MI trials of maximal isometric contractions (100% MVC_MI). Mental fatigue was assessed after each block using a visual analogue scale (VAS). We assessed maximal isometric force before, during and after MI sessions. We also assessed MI ability from self-report ratings and skin conductance recordings. Results showed a logarithmic pattern of increase in mental fatigue over the course of MI, which was superior during 100% MVC_MI. Unexpectedly, maximal force improved during 100% MVC_MI between the 1st and 2nd evaluations but remained unchanged during 20% MVC_MI. MI ease and vividness improved during 100% MVC_MI, with a positive association between phasic skin conductance and VAS mental fatigue scores. Conversely, subjective measures revealed decreased MI ability during 20% MVC_MI. Mental fatigue did not hamper the priming effects of MI on maximal force performance, nor MI's ability for tasks involving high physical demands. By contrast, mental fatigue impaired MI vividness and elicited boredom effects in the case of motor tasks with low physical demands.

Relationship between Corticospinal Excitability While Gazing at the Mirror and Motor Imagery Ability

Mirror therapy (MT) helps stroke survivors recover motor function. Previous studies have reported that an individual's motor imagery ability is related to the areas of brain activity during motor imagery and the effectiveness of motor imagery training. However, the relationship between MT and motor imagery ability and between corticospinal tract excitability during mirror gazing, an important component of MT, and motor imagery ability is unclear. This study determined whether the motor-evoked potential (MEP) amplitude while gazing at the mirror relates to participants' motor imagery abilities. Twenty-four healthy right-handed adults (seven males) were recruited. Transcranial magnetic stimulation was performed while gazing at the mirror, and MEP of the first dorsal interosseous muscle of the right hand were measured. Motor imagery ability was measured using the Kinesthetic and Visual Imagery Questionnaire (KVIQ), which assesses the vividness of motor imagery ability. Additionally, a mental chronometry (MC) task was used to assess time aspects. The results showed a significant moderate correlation between changes in MEP amplitude values while gazing at the mirror, as compared with resting conditions, and assessment scores of KVIQ. This study shows that corticospinal excitability because of mirror gazing may be related to the vividness of motor imagery ability.

The role of the primary motor cortex in motor imagery: A theta burst stimulation study

While mentally simulated actions activate similar neural structures to overt movement, the role of the primary motor cortex (PMC) in motor imagery remains disputed. The aim of the study was to use continuous theta burst stimulation (cTBS) to modulate corticospinal activity to investigate the putative role of the PMC in implicit motor imagery in young adults with typical and atypical motor ability. A randomized, double blind, sham-controlled, crossover, offline cTBS protocol was applied to 35 young adults. During three separate sessions, adults with typical and low motor ability (developmental coordination disorder [DCD]), received active cTBS to the PMC and supplementary motor area (SMA), and sham stimulation to either the PMC or SMA. Following stimulation, participants completed measures of motor imagery (i.e., hand rotation task) and visual imagery (i.e., letter number rotation task). Although active cTBS significantly reduced corticospinal excitability in adults with typical motor ability, neither task performance was altered following active cTBS to the PMC or SMA, compared to performance after sham cTBS. These results did not differ across motor status (i.e., typical motor ability and DCD). These findings are not consistent with our hypothesis that the PMC (and SMA) is directly involved in motor imagery. Instead, previous motor cortical activation observed during motor imagery may be an epiphenomenon of other neurophysiological processes and/or activity within brain regions involved in motor imagery. This study highlights the need to consider multi-session theta burst stimulation application and its neural effects when probing the putative role of motor cortices in motor imagery.

Effects of action observation and motor imagery of walking on the corticospinal and spinal motoneuron excitability and motor imagery ability in healthy participants

Action observation (AO) and motor imagery (MI) are used for the rehabilitation of patients who face difficulty walking. Rehabilitation involving AO, MI, and AO combined with MI (AO+MI) facilitates gait recovery after neurological disorders. However, the mechanism by which it positively affects gait function is unclear. We previously examined the neural mechanisms underlying AO and MI of walking, focusing on AO+MI and corticospinal and spinal motor neuron excitability, which play important roles in gait function. Herein, we investigated the effects of a short intervention using AO+MI of walking on the corticospinal and spinal motor neuron excitability and MI ability of participants. Twelve healthy individuals participated in this study, which consisted of a 20 min intervention. Before the experiment, we measured MI ability using the Vividness of Movement Imagery Questionnaire-2 (VMIQ-2). We used motor evoked potential and F-wave measurements to evaluate the corticospinal and spinal motor neuron excitability at rest, pre-intervention, 0 min, and 15 min post-intervention. We also measured corticospinal excitability during MI of walking and the participant’s ability to perform MI using a visual analog scale (VAS). There were no significant changes in corticospinal and spinal motor neuron excitability during and after the intervention using AO+MI (p>0.05). The intervention temporarily increased VAS scores, thus indicating clearer MI (p<0.05); however, it did not influence corticospinal excitability during MI of walking (p>0.05). Furthermore, there was no significant correlation between the VMIQ-2 and VAS scores and changes in corticospinal and spinal motor neuron excitability. Therefore, one short intervention using AO+MI increased MI ability in healthy individuals; however, it was insufficient to induce plastic changes at the cortical and spinal levels. Moreover, the effects of intervention using AO+MI were not associated with MI ability. Our findings provide information about intervention using AO+MI in healthy individuals and might be helpful in planning neurorehabilitation strategies.

Motor Imagery: How to Assess, Improve Its Performance, and Apply It for Psychosis Diagnostics

With this review, we summarize the state-of-the-art of scientific studies in the field of motor imagery (MI) and motor execution (ME). We composed the brain map and description that correlate different brain areas with the type of movements it is responsible for. That gives a more complete and systematic picture of human brain functionality in the case of ME and MI. We systematized the most popular methods for assessing the quality of MI performance and discussed their advantages and disadvantages. We also reviewed the main directions for the use of transcranial magnetic stimulation (TMS) in MI research and considered the principal effects of TMS on MI performance. In addition, we discuss the main applications of MI, emphasizing its use in the diagnostics of various neurodegenerative disorders and psychoses. Finally, we discuss the research gap and possible improvements for further research in the field.

A Noninvasive BCI System for 2D Cursor Control Using a Spectral-Temporal Long Short-Term Memory Network

Two-dimensional cursor control is an important and challenging problem in the field of electroencephalography (EEG)-based brain computer interfaces (BCIs) applications. However, most BCIs based on categorical outputs are incapable of generating accurate and smooth control trajectories. In this article, a novel EEG decoding framework based on a spectral-temporal long short-term memory (stLSTM) network is proposed to generate control signals in the horizontal and vertical directions for accurate cursor control. Precisely, the spectral information is used to decode the subject's motor imagery intention, and the error-related P300 information is used to detect a deviation in the movement trajectory. The concatenated spectral and temporal features are fed into the stLSTM network and mapped to the velocities in vertical and horizontal directions of the 2D cursor under the velocity-constrained (VC) strategy, which enables the decoding network to fit the velocity in the imaginary direction and simultaneously suppress the velocity in the non-imaginary direction. This proposed framework was validated on a public real BCI control dataset. Results show that compared with the state-of-the-art method, the RMSE of the proposed method in the non-imaginary directions on the testing sets of 2D control tasks is reduced by an average of 63.45%. Besides, the visualization of the actual trajectories distribution of the cursor also demonstrates that the decoupling of velocity is capable of yielding accurate cursor control in complex path tracking tasks and significantly improves the control accuracy.

Time course changes in corticospinal excitability during repetitive peripheral magnetic stimulation combined with motor imagery

Repetitive peripheral magnetic stimulation (rPMS) induces proprioceptive afferents and facilitates corticospinal excitability. Short-term sessions of rPMS combined with motor imagery (MI) enhance corticospinal excitability more than rPMS alone. However, it is not clear how long the intervention of rPMS combined with MI would be needed to facilitate corticospinal excitability. Therefore, we investigated the time course change in corticospinal excitability during the combination of rPMS and MI. Thirteen healthy volunteers participated in a 20-min intervention under the following three experimental conditions on different days: rPMS, MI, and rPMS combined with MI (rPMS + MI). In the rPMS and rPMS + MI, the participants were delivered rPMS, which was 25 Hz, 2 s/train at 1.5 × of the train intensity induced muscle contractions, through the wrist extensor muscles. In the MI and rPMS + MI, the participants repeatedly imagined wrist movements for 2 s. Motor evoked potentials (MEPs) were recorded from the extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscles every 5 min for each condition. The MEP amplitudes of the ECR after > 10 min of intermittent rPMS combined with MI were greater than baseline. The MEP amplitude of the ECR in rPMS + MI was greater than that in rPMS condition after 20 min of intervention. The present results suggest that over 10 min of intermittent rPMS combined with MI facilitates corticospinal excitability, and that the effect of rPMS combined with MI on corticospinal excitability might be greater than that of rPMS alone.

Thenar Muscle Motor Imagery Increases Spinal Motor Neuron Excitability of the Abductor Digiti Minimi Muscle

When a person attempts intended finger movements, unintended finger movement also occur, a phenomenon called “enslaving”. Given that motor imagery (MI) and motor execution (ME) share a common neural foundation, we hypothesized that the enslaving effect on the spinal motor neuron excitability occurs during MI. To investigate this hypothesis, electromyography (EMG) and F-wave analysis were conducted in 11 healthy male volunteers. Initially, the EMG activity of the left abductor digiti minimi (ADM) muscle during isometric opposition pinch movement by the left thumb and index finger at 50% maximal effort was compared with EMG activity during the Rest condition. Next, the F-wave and background EMG recordings were performed under the Rest condition, followed by the MI condition. Specifically, in the Rest condition, subjects maintained relaxation. In the MI condition, they imagined isometric left thenar muscle activity at 50% maximal voluntary contraction (MVC). During ME, ADM muscle activity was confirmed. During the MI condition, both F-wave persistence and the F-wave/M-wave amplitude ratio obtained from the ADM muscle were significantly increased compared with that obtained during the Rest condition. No difference was observed in the background EMG between the Rest and MI conditions. These results suggest that MI of isometric intended finger muscle activity at 50% MVC facilitates spinal motor neuron excitability corresponding to unintended finger muscle. Furthermore, MI may induce similar modulation of spinal motor neuron excitability as actual movement.

Behavioural indexes of movement imagery ability are associated with the magnitude of corticospinal adaptation following movement imagery training

Movement imagery (MI) is a cognitive process wherein an individual simulates themselves performing a movement in the absence of physical movement. The current paper reports an examination of the relationship between behavioural indexes of MI ability and the magnitude of corticospinal adaptation following MI training. Behavioural indexes of MI ability included data from a questionnaire (MIQ-3), a mental chronometry task, and a hand laterality judgment task. For the measure of corticospinal adaptation, single-pulse transcranial magnetic stimulation (TMS) was administered to elicit thumb movements to determine the representation of thumb movements before and after MI training. MI training involved participants imagining themselves moving their thumb in the opposite direction to the dominant direction of the TMS-evoked movements prior to training. Pre/post-training changes in the direction and velocity of TMS-evoked thumb movements indicated the magnitude of adaptation following MI training. The two main findings were: 1) a positive relationship was found between the MIQ-3 and the pre/post-training changes in the direction of TMS-evoked thumb movements; and 2) a negative relationship between the mental chronometry measure and both measures of corticospinal adaptation following MI training. These results indicate that both ease of imagery and timing of imagery could predict the magnitude of neuroplastic adaptation following MI training. Thus, both these measures may be considered when assessing imagery ability and determining who might benefit from MI interventions.

Does Real-Time Feedback Affect Sensorimotor EEG Patterns in Routine Motor Imagery Practice?

Background. Motor imagery engages much of the same neural circuits as an overt movement. Therefore, the mental rehearsal of movements is often used to supplement physical training and might aid motor neurorehabilitation after stroke. One attempt to capture the brain’s involvement in imagery involves the use, as a marker, of the depression or event-related desynchronization (ERD) of thalamocortical sensorimotor rhythms found in a human electroencephalogram (EEG). Using fast real-time processing, it is possible to make the subject aware of their own brain reactions or—even better—to turn them into actions through a technology called the brain–computer interface (BCI). However, it remains unclear whether BCI-enabled imagery facilitates a stronger or qualitatively different brain response compared to the open-loop training. Methods. Seven healthy volunteers who were experienced in both closed and open-loop motor imagery took part in six experimental sessions over a period of 4.5 months, in which they performed kinesthetic imagery of a previously known set of finger and arm movements with simultaneous 30-channel EEG acquisition. The first and the last session mostly consisted of feedback trials in which the subjects were presented with the classification results of the EEG patterns in real time; during the other sessions, no feedback was provided. Spatiotemporal and amplitude features of the ERD patterns concomitant with imagery were compared across experimental days and between feedback conditions using linear mixed-effects modeling. Results. The main spatial sources of ERD appeared to be highly stable across the six experimental days, remaining nearly identical in five of seven subjects (Pearson’s ρ > 0.94). Only in one subject did the spatial pattern of activation statistically significantly differ (p = 0.009) between the feedback and no-feedback conditions. Real-time visual feedback delivered through the BCI did not significantly increase the ERD strength. Conclusion. The results imply that the potential benefits of MI could be yielded by well-habituated subjects with a simplified open-loop setup, e.g., through at-home self-practice.

Sonification of combined action observation and motor imagery: Effects on corticospinal excitability

Action observation and motor imagery are valuable strategies for motor learning. Their simultaneous use (AOMI) increases neural activity, with related benefits for motor learning, compared to the two strategies alone. In this study, we explored how sonification influences AOMI. Twenty-five participants completed a practice block based on AOMI, motor imagery and physical execution of the same action. Participants were divided into two groups: An experimental group that practiced with sonification during AOMI (sAOMI), and a control group, which did not receive any extrinsic feedback. Corticospinal excitability at rest and during action observation and AOMI was assessed before and after practice, with and without sonification sound, to test the development of an audiomotor association. The practice block increased corticospinal excitability in all testing conditions, but sonification did not affect this. In addition, we found no differences in action observation and AOMI, irrespective of sonification. These results suggest that, at least for simple tasks, sonification of AOMI does not influence corticospinal excitability; In these conditions, sonification may have acted as a distractor. Future studies should further explore the relationship between task complexity, value of auditory information and action, to establish whether sAOMI is a valuable for motor learning.

Effect of repetitive peripheral magnetic stimulation combined with motor imagery on the corticospinal excitability of antagonist muscles

OBJECTIVE

Repetitive peripheral magnetic stimulation (rPMS) combined with motor imagery facilitates the corticospinal excitability of the agonist muscles. However, the effects of rPMS combined with motor imagery on the corticospinal excitability of the antagonist muscles are unclear. This is an important aspect for applying rPMS in neurorehabilitation for sensorimotor dysfunction. Therefore, we investigated the real-time changes of corticospinal excitability of antagonist muscles during rPMS combined with motor imagery.

METHODS

Fourteen healthy volunteers underwent four different experimental conditions: rest, rPMS, motor imagery, and rPMS combined with motor imagery (rPMS + motor imagery). In the rPMS and rPMS + motor imagery conditions, rPMS (25 Hz, 1600 ms/train, 1.5× of the motor threshold) was delivered to the dorsal side of the forearm. In motor imagery and rPMS + motor imagery, the participant imagined wrist extension movements. Transcranial magnetic stimulation was delivered to record motor-evoked potentials of the antagonist muscle during experimental interventions.

RESULTS

The motor-evoked potential (normalized by rest condition) values indicated no difference between rPMS, motor imagery, and rPMS + motor imagery.

CONCLUSION

These results suggest that rPMS combined with motor imagery has no effect on the corticospinal excitability of the antagonist muscles and highlight the importance of investigating the effects of rPMS combined with motor imagery at the spinal level.

Combined action observation and motor imagery: An intervention to combat the neural and behavioural deficits associated with developmental coordination disorder

Action observation (AO) and motor imagery (MI) have been used separately across different populations to alleviate movement impairment. Recently these two forms of covert motor simulation have been combined (combined action observation and motor imagery; AOMI), resulting in greater neurophysiological activity in the motor system, and more favourable behavioural outcomes when compared to independent AO and MI. This review aims to outline how some of the neural deficits associated with developmental coordination disorder (DCD) are evident during AO and MI, and highlight how these motor simulation techniques have been used independently to improve motor skill learning in children in this population. The growing body of evidence indicating that AOMI is superior to the independent use of either AO and MI is then synthesised and discussed in the context of children with DCD. To conclude, recommendations to optimise the delivery of AOMI for children with DCD are provided and future avenues for research are highlighted.

Peripheral Electrical Stimulation Modulates Cortical Beta-Band Activity

Low-frequency peripheral electrical stimulation using a matrix electrode (PEMS) modulates spinal nociceptive pathways. However, the effects of this intervention on cortical oscillatory activity have not been assessed yet. The aim of this study was to investigate the effects of low-frequency PEMS (4 Hz) on cortical oscillatory activity in different brain states in healthy pain-free participants. In experiment 1, PEMS was compared to sham stimulation. In experiment 2, motor imagery (MI) was used to modulate the sensorimotor brain state. PEMS was applied either during MI-induced oscillatory desynchronization (concurrent PEMS) or after MI (delayed PEMS) in a cross-over design. For both experiments, PEMS was applied on the left forearm and resting-state electroencephalography (EEG) was recording before and after each stimulation condition. Experiment 1 showed a significant decrease of global resting-state beta power after PEMS compared to sham (p = 0.016), with a median change from baseline of −16% for PEMS and −0.54% for sham. A cluster-based permutation test showed a significant difference in resting-state beta power comparing pre- and post-PEMS (p = 0.018) that was most pronounced over bilateral central and left frontal sensors. Experiment 2 did not identify a significant difference in the change from baseline of global EEG power for concurrent PEMS compared to delayed PEMS. Two cluster-based permutation tests suggested that frontal beta power may be increased following both concurrent and delayed PEMS. This study provides novel evidence for supraspinal effects of low-frequency PEMS and an initial indication that the presence of a cognitive task such as MI may influence the effects of PEMS on beta activity. Chronic pain has been associated with changes in beta activity, in particular an increase of beta power in frontal regions. Thus, brain state-dependent PEMS may offer a novel approach to the treatment of chronic pain. However, further studies are warranted to investigate optimal stimulation conditions to achieve a reduction of pain.

Enhancement of Event-Related Desynchronization in Motor Imagery Based on Transcranial Electrical Stimulation

Due to the individual differences controlling brain-computer interfaces (BCIs), the applicability and accuracy of BCIs based on motor imagery (MI-BCIs) are limited. To improve the performance of BCIs, this article examined the effect of transcranial electrical stimulation (tES) on brain activity during MI. This article designed an experimental paradigm that combines tES and MI and examined the effects of tES based on the measurements of electroencephalogram (EEG) features in MI processing, including the power spectral density (PSD) and dynamic event-related desynchronization (ERD). Finally, we investigated the effect of tES on the accuracy of MI classification using linear discriminant analysis (LDA). The results showed that the ERD of the μ and β rhythms in the left-hand MI task was enhanced after electrical stimulation with a significant effect in the tDCS group. The average classification accuracy of the transcranial alternating current stimulation (tACS) group and transcranial direct current stimulation (tDCS) group (88.19% and 89.93% respectively) were improved significantly compared to the pre-and pseudo stimulation groups. These findings indicated that tES can improve the performance and applicability of BCI and that tDCS was a potential approach in regulating brain activity and enhancing valid features during noninvasive MI-BCI processing.

A Study on the Effect of Mental Practice Using Motor Evoked Potential-Based Neurofeedback

This study aimed to investigate whether the effect of mental practice (motor imagery training) can be enhanced by providing neurofeedback based on transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEP). Twenty-four healthy, right-handed subjects were enrolled in this study. The subjects were randomly allocated into two groups: a group that was given correct TMS feedback (Real-FB group) and a group that was given randomized false TMS feedback (Sham-FB group). The subjects imagined pushing the switch with just timing, when the target circle overlapped a cross at the center of the computer monitor. In the Real-FB group, feedback was provided to the subjects based on the MEP amplitude measured in the trial immediately preceding motor imagery. In contrast, the subjects of the Sham-FB group were provided with a feedback value that was independent of the MEP amplitude. TMS was applied when the target, moving from right to left, overlapped the cross at the center of the screen, and the MEP amplitude was measured. The MEP was recorded in the right first dorsal interosseous muscle. We evaluated the pre-mental practice and post-mental practice motor performance in both groups. As a result, a significant difference was observed in the percentage change of error values between the Real-FB group and the Sham-FB group. Furthermore, the MEP was significantly different between the groups in the 4th and 5th sets. Therefore, it was suggested that TMS-induced MEP-based neurofeedback might enhance the effect of mental practice.

The Vividness of Motor Imagery Is Correlated With Corticospinal Excitability During Combined Motor Imagery and Action Observation

The present study aimed to investigate the relationship between motor imagery (MI) assessment (ability and quality) and neurophysiological assessment [transcranial magnetic stimulation (TMS)-induced motor-evoked potentials (MEPs)] during combined MI and action observation (AO; MI + AO). Sixteen subjects completed an MI task playing the piano with both hands, and neurophysiological assessment was performed during the MI task. The Movement Imagery Questionnaire-Revised was adopted to evaluate MI ability, while the visual analogue scale (VAS) was adopted to evaluate MI quality. A TMS pulse was delivered during the MI task, and MEPs were subsequently recorded in the abductor pollicis brevis (APB). We found a significant positive correlation between the VAS score and the TMS-induced MEPs (ρ = 0.497, p < 0.001). These findings suggest that the VAS score could potentially reflect the corticospinal excitability during MI + AO, particularly in complex MI tasks.

Task-independent Electrophysiological Correlates of Motor Imagery Ability from Kinaesthetic and Visual Perspectives

Motor imagery (MI) ability is highly subjective, as indicated by the individual scores of the MIQ-3 questionnaire, and poor imagers compensate for the difficulty in performing MI with larger cerebral activations, as demonstrated by MI studies involving hands/limbs. In order to identify general, task-independent MI ability correlates, 16 volunteers were stratified with MIQ-3. The scores in the kinaesthetic (K) and 1st-person visual (V) perspectives were associated with EEG patterns obtained during K-MI and V-MI of the same complex MIQ-3 movements during these MI tasks (Spearman's correlation, significance at <0.05, SnPM corrected). EEG measures were relative to rest (relaxation, closed eyes), and based on six electrode clusters both for band spectral content and connectivity (Granger causality). Lower K-MI ability was associated with greater theta decreases during tasks in fronto-central clusters and greater inward information flow to prefrontal clusters for theta, high alpha and beta bands. On the other hand, power band relative decreases were associated with V-MI ability in fronto-central clusters for low alpha and left fronto-central and both centro-parietal clusters for beta bands. The results thus suggest different computational mechanisms for MI-V and MI-K. The association between low alpha/beta desynchronization and V-MIQ scores and between theta changes and K-MIQ scores suggest a cognitive effort with greater cerebral activation in participants with lower V-MI ability. The association between information flow to prefrontal hub and K-MI ability suggest the need for a continuous update of information to support MI-related executive functions in subjects with poor K-MI ability.

Performing the hand laterality judgement task does not necessarily require motor imagery

When people judge the laterality of rotated hand images, that is they perform the laterality judgement task (LJT), they are thought to use motor imagery. However, recent studies have suggested that its completion does not necessarily require the use of motor imagery. In this study, we investigated whether and how many people preferentially use motor imagery to perform the LJT in 37 healthy adults. We assessed the presence of behavioural features associated with motor imagery at the individual level, namely, the linear angle-response time (RT) relationship and the biomechanical constraints effect in the LJT and in the same-different judgement task (SDJT), in which people are not thought to use motor imagery. We found that at most 50% of participants showed both behavioural features in the palmar view condition of the LJT. Moreover, this proportion did not differ from that in the dorsal view condition of the LJT or that in both view conditions of the SDJT. These results demonstrate that a motor imagery-based strategy is not universally and specifically used to perform the LJT. Therefore, previous results of the LJT, in particular, regarding the biomechanical constraints effect, should be reinterpreted in light of our findings.

Motor Imagery Development in Children: Changes in Speed and Accuracy With Increasing Age

Although motor imagery has been pointed as a promising strategy for the rehabilitation of children with neurological disorders, information on their development throughout childhood and adolescence is still scarce. For instance, it is still unclear at what age they reach a development comparable to the motor imagery performance observed in adults. Herein we used a mental rotation task to assess motor imagery in 164 typically developing children and adolescents, which were divided into four age groups (6-7, 8-9, 10-11, and 12-13 years) and 30 adults. The effects of biomechanical constraints, accuracy, and reaction time of the mental rotation task were considered. ANOVA showed that all groups had the effect of biomechanical restrictions of the mental rotation task. We found a group effect for accuracy [F (4, 180) = 17,560; p < 0.00; η2 = 3.79] and reaction time [F (4, 180) = 17.5; p < 0.001, η2 = 0.615], with the results of children groups 6-7 and 8-9 years being significantly lower than the other groups (p < 0.05). In all the analyses, there were no differences regarding accuracy and reaction time among the participants of the age groups 10-11 and 12-13 years and adults (p > 0.05). Concluding, children aged 6-7 years were able to perform motor imagery, motor imagery ability improved as the participants' ages increased, and children aged 10 and over-performed similarly to adults.

Motor activation is modulated by visual experience during cyclic gait observation: A transcranial magnetic stimulation study

Transcranial magnetic stimulation (TMS) has been widely utilized to noninvasively explore the motor system during the observation of human movement. However, few studies have characterized motor cortex activity during periodic gait observation. Thus, this study examined the effects of an observer's visual experience and/or intention to imitate on corticospinal excitability during the observation of another's gait. Twenty-six healthy volunteers were included in this study and allocated to two different groups. Participants in the visual experience group had formal experience with gait observation (physical therapist training), while those in the control group did not. Motor-evoked potentials induced by TMS in the tibialis anterior and soleus muscles were measured as surrogates of corticospinal excitability. Participants were seated and, while resting, they observed a demonstrator's gait or observed it with the intention to subsequently reproduce it. Compared with the resting state, cyclic gait observation led to significant corticospinal facilitation in the tibialis anterior and soleus muscles. However, this pattern of corticospinal facilitation in the measured muscles was not coupled to the pattern of crural muscle activity during actual gait and was independent of the step cycle. This motor cortex facilitation effect during gait observation was enhanced by the observer's visual experience in a manner that was not step cycle-dependent, while the observer's intent to imitate did not affect corticospinal excitatory input to either muscle. In addition, visual experience did not modulate corticospinal excitability in gait-related crural muscles. Our findings indicate that motor cortex activity during gait observation is not in line with the timing of muscle activity during gait execution and is modulated by an individual's gait observation experience. These results suggest that visual experience acquired from repetitive gait observation may facilitate the motor system's control on bipedal walking, but may not promote the learning of muscle activity patterns.

The Role of Movement Representation Techniques in the Motor Learning Process: A Neurophysiological Hypothesis and a Narrative Review

We present a neurophysiological hypothesis for the role of motor imagery (MI) and action observation (AO) training in the motor learning process. The effects of movement representation in the brain and those of the cortical–subcortical networks related to planning, executing, adjusting, and automating real movements share a similar neurophysiological activity. Coupled with the influence of certain variables related to the movement representation process, this neurophysiological activity is a key component of the present hypothesis. These variables can be classified into four domains: physical, cognitive–evaluative, motivational–emotional, and direct-modulation. The neurophysiological activity underlying the creation and consolidation of mnemonic representations of motor gestures as a prerequisite to motor learning might differ between AO and MI. Together with variations in cognitive loads, these differences might explain the differing results in motor learning. The mirror neuron system appears to function more efficiently through AO training than MI, and AO is less demanding in terms of cognitive load than MI. AO might be less susceptible to the influence of variables related to movement representation.

EFFECT OF MOTOR IMAGERY TRAINING IN COMBINATION WITH ELECTROMYOGRAPHY-TRIGGERED ELECTRICAL STIMULATION IN STROKE WITH HEMIPLEGIA PATIENTS: A RANDOMIZED CONTROLLED STUDY

Recently, motor imagery training combined with electromyography-triggered electrical stimulation (MIT EMG-ES) has been reported as a remedial treatment for stroke patients. However, the clinical evidence of the effect is still lacking. To investigate the effect of MIT EMG-ES on lower extremities and activities of daily of living (ADL) in patients with stroke, the participants were randomly assigned to an experimental group ([Formula: see text]) or control group ([Formula: see text]). The experimental group underwent MIT EMG-ES, whereas the control group performed underwent motor imagery training. In addition, both groups received the same conventional rehabilitation therapy. All participants underwent treatment for 30[Formula: see text]min a day, 5 sessions per week, for 4 weeks. Lower extremities function was measured by the Fugl–Meyer Assessment Lower Extremity (FMA-LE), Timed Up-and-Go (TUG) test and 10 m Walk (10[Formula: see text]MW) test. ADL were measured by the Korea version of the Modified Barthel Index (K-MBI). The experimental group except for the FMA-LE group showed more improvement in TUG and 10[Formula: see text]MW test scores than the control group ([Formula: see text]). The effect size showed FMA-LE, TUG, and 10[Formula: see text]MW test (0.7, 1.0, 0.7, respectively). However, there was no statistically significant difference between the two groups in K-MBI ([Formula: see text]). Our findings suggest that MIT EMG-ES may be a novel treatment for lower extremities function in patients with stroke better than MIT alone.

Cerebral haemodynamics during motor imagery of self-feeding with chopsticks: differences between dominant and non-dominant hand

Purpose: Motor imagery is defined as a dynamic state during which a subject mentally simulates a given action without overt movements. Our aim was to use near-infrared spectroscopy to investigate differences in cerebral haemodynamics during motor imagery of self-feeding with chopsticks using the dominant or non-dominant hand.Materials and methods: Twenty healthy right-handed people participated in this study. The motor imagery task involved eating sliced cucumber pickles using chopsticks with the dominant (right) or non-dominant (left) hand. Activation of regions of interest (pre-supplementary motor area, supplementary motor area, pre-motor area, pre-frontal cortex, and sensorimotor cortex was assessed.Results: Motor imagery vividness of the dominant hand tended to be significantly higher than that of the non-dominant hand. The time of peak oxygenated haemoglobin was significantly earlier in the right pre-frontal cortex than in the supplementary motor area and left pre-motor area. Haemodynamic correlations were detected in more regions of interest during dominant-hand motor imagery than during non-dominant-hand motor imagery.Conclusions: Haemodynamics might be affected by differences in motor imagery vividness caused by variations in motor manipulation.

What is the effect of bodily illusions on corticomotoneuronal excitability? A systematic review

Background

This systematic review aimed to summarise and critically appraise the evidence for the effect of bodily illusions on corticomotoneuronal excitability.

Methods

Five databases were searched, with two independent reviewers completing study inclusion, risk of bias, transcranial magnetic stimulation (TMS) reporting quality, and data extraction. Included studies evaluated the effect of an illusion that altered perception of the body (and/or its movement) on excitability of motor circuitry in healthy, adult, human participants. Studies were required to: use TMS to measure excitability and/or inhibition; report quantitative outcomes (e.g., motor evoked potentials); compare the illusion to a control or active comparison condition; evaluate that an illusion had occurred (e.g., measured illusion strength/presence).

Results

Of 2,257 studies identified, 11 studies (14 experiments) were included, evaluating kinaesthetic illusions (n = 5), a rubber hand illusion (RHI) paradigm (n = 5), and a missing limb illusion (n = 1). Kinaesthetic illusions (induced via vision/tendon vibration) increased corticomotoneuronal excitability. Conflicting effects were found for traditional, visuotactile RHIs of a static hand. However, embodying a hand and then observing it move (“self-action”) resulted in decreased corticomotoneuronal excitability and increased silent period duration (a measure of Gamma-Aminobutynic acid [GABA]_B-mediated intracortical inhibition in motor cortex), with the opposite occurring (increased excitability, decreased inhibition) when the fake hand was not embodied prior to observing movement (“other-action”). Visuomotor illusions manipulating agency had conflicting results, but in the lower risk study, illusory agency over movement resulted in a relative decrease in corticomotoneuronal excitability. Last, an illusion of a missing limb reduced corticomotoneuronal excitability.

Conclusion

While evidence for the effect of bodily illusions on corticomotoneuronal excitability was limited (only 14 experiments) and had a high risk of bias, kinaesthetic illusions and illusions of embodying a hand (and seeing it move), had consistent effects. Future investigations into the role of embodiment and the illusion strength on corticomotoneuronal excitability and inhibition are warranted.

Kinaesthetic illusion shapes the cortical plasticity evoked by action observation

KEY POINTS

The combination of action observation (AO) and a peripheral nerve stimulation has been shown to induce plasticity in the primary motor cortex (M1). However, using peripheral nerve stimulation little is known about the specificity of the sensory inputs. The current study, using muscle tendon vibration to stimulate muscle spindles and transcranial magnetic stimulation to assess M1 excitability, investigated whether a proprioceptive stimulation leading to a kinaesthetic illusion of movement (KI) was able to evoke M1 plasticity when combined with AO. M1 excitability increased immediately and up to 60 min after AO-KI stimulation as a function of the vividness of the perceived illusion, and only when the movement directions of AO and KI were congruent. Tactile stimulation coupled with AO and KI alone were not sufficient to induce M1 plasticity. This methodology might be proposed to subjects during a period of immobilization to promote M1 activity without requiring any voluntary movement.

ABSTRACT

Physical practice is crucial to evoke cortical plasticity, but motor cognition techniques, such as action observation (AO), have shown their potentiality in promoting it when associated with peripheral afferent inputs, without the need of performing a movement. Here we investigated whether the combination of AO and a proprioceptive stimulation, able to evoke a kinaesthetic illusion of movement (KI), induced plasticity in the primary motor cortex (M1). In the main experiment, the role of congruency between the observed action and the illusory movement was explored together with the importance of the specificity of the sensory input modality (proprioceptive vs. tactile stimulation) to induce plasticity in M1. Further, a control experiment was carried out to assess the role of the mere kinaesthetic illusion on M1 excitability. Results showed that the combination of AO and KI evoked plasticity in M1, with an increase of the excitability immediately and up to 60 min after the conditioning protocol (P always <0.05). Notably, a significant increase in M1 excitability occurred only when the directions of the observed and illusory movements were congruent. Further, a significant positive linear relationship was found between the amount of M1 excitability increase and the vividness of the perceived illusion (P = 0.03). Finally, the tactile stimulation coupled with AO was not sufficient to induce changes in M1 excitability as well as the KI alone. All these findings indicate the importance of combining different sensory input signals to induce plasticity in M1, and that proprioception is the most suitable sensory modality to allow it.

Imagery strategy affects spinal motor neuron excitability: using kinesthetic and somatosensory imagery

Motor imagery is the mental rehearsal of a movement within working memory. Reduction of spinal motor neuron excitability has been demonstrated after stroke, and motor imagery may increase spinal motor neuron excitability in patients with a motor deficit. However, spinal motor neuron excitability varies depending on the imagery strategy used. In this study, we examined spinal motor neuron excitability during kinesthetic, somatosensory, and combined imagery. Healthy adult volunteers (n=14) were recruited for F-wave recording. The F-wave was measured during relaxation to determine baseline levels, followed by measurement during the three imagery trials performed in a random order. In the somatosensory imagery (SI) trial, participants imagined tactile and pressure perception of the thumb finger pulp during holding a pinch meter. In the kinesthetic imagery (KI) trial, participants imagined muscle contraction during isometric thenar muscle activity at 50% maximal voluntary contraction. In the combined KI and SI trial, participants performed the KI and SI simultaneously. After F-wave recording, participants evaluated the difficulty of each imagery trial using a five-point Likert scale. Persistence during SI and KI was significantly higher than that at rest. The F/M amplitude ratio during KI was significantly higher than that at rest. The five-point Likert scale score of the combined KI and SI was significantly lower than that of KI. KI may increase spinal motor neuron excitability over that of SI. Thus, it is important to consider the sensory modality chosen for imagery during rehabilitation.

Effects of Leg Motor Imagery Combined With Electrical Stimulation on Plasticity of Corticospinal Excitability and Spinal Reciprocal Inhibition

Motor imagery (MI) combined with electrical stimulation (ES) enhances upper-limb corticospinal excitability. However, its after-effects on both lower limb corticospinal excitability and spinal reciprocal inhibition remain unknown. We aimed to investigate the effects of MI combined with peripheral nerve ES (MI + ES) on the plasticity of lower limb corticospinal excitability and spinal reciprocal inhibition. Seventeen healthy individuals performed the following three tasks on different days, in a random order: (1) MI alone; (2) ES alone; and (3) MI + ES. The MI task consisted of repetitive right ankle dorsiflexion for 20 min. ES was percutaneously applied to the common peroneal nerve at a frequency of 100 Hz and intensity of 120% of the sensory threshold of the tibialis anterior (TA) muscle. We examined changes in motor-evoked potential (MEP) of the TA (task-related muscle) and soleus muscle (SOL; task-unrelated muscle). We also examined disynaptic reciprocal inhibition before, immediately after, and 10, 20, and 30 min after the task. MI + ES significantly increased TA MEPs immediately and 10 min after the task compared with baseline, but did not change the task-unrelated muscle (SOL) MEPs. MI + ES resulted in a significant increase in the magnitude of reciprocal inhibition immediately and 10 min after the task compared with baseline. MI and ES alone did not affect TA MEPs or reciprocal inhibition. MI combined with ES is effective in inducing plastic changes in lower limb corticospinal excitability and reciprocal Ia inhibition.

Vividness and accuracy: Two independent aspects of motor imagery

Motor imagery is the mental execution of an action without any actual movement. Although numerous studies have utilized questionnaires to evaluate the vividness of motor imagery, it remains unclear whether it is related to the accuracy of motor imagery. To examine the relationship between vividness and accuracy, we investigated brain activity during kinesthetic and visual motor imagery, by using a novel sequential finger-tapping task. We estimated accuracy by measuring the fidelity of the actual performance and evaluated vividness by using a visual analog scale. We found that accuracy of visual motor imagery was correlated with the activity in the left visual cortex, as well as with bilateral sensorimotor regions. In contrast, vividness of visual motor imagery was associated with the activity in the right orbitofrontal cortex. However, there was no correlation in the brain activity between the right orbitofrontal cortex and visuomotor regions or between vividness and accuracy of motor imagery. In addition, we did not find any correlation in the kinesthetic imagery condition. We conclude that vividness of visual motor imagery is associated with the right orbitofrontal cortex and is independent of processes occurring in sensorimotor regions, which would be responsible for the accuracy of visual motor imagery.

Does the duration of motor imagery affect the excitability of spinal anterior horn cells?

PURPOSE

Motor imagery, the process of imagining a physical action, has been shown to facilitate the excitability of spinal anterior horn cells. In the acute phase after a stroke, the excitability of spinal anterior horn cells is significantly reduced, which leads to motor deficits. This loss of movement can be prevented by increasing the excitability of spinal anterior horn cells immediately following an injury. Motor imagery is an effective method for facilitating the excitability of spinal anterior horn cells in patients with impaired movement; however, the optimal duration for motor imagery is unclear.

MATERIALS AND METHODS

To investigate time-dependent changes in spinal anterior horn cell excitability during motor imagery, healthy adult participants were recruited to measure the F-wave, an indicator of anterior horn cell excitability. F-waves were measured from participants at baseline, during motor imagery, and post-motor imagery. During motor imagery, participants imagined isometric thenar muscle activity at 50% maximum voluntary contraction for 5 min. F-waves were measured at 1, 3, and 5 min after beginning motor imagery and analysed for persistence and F/M amplitude ratio.

RESULTS

Persistence and F/M amplitude ratios at 1- and 3-min after motor imagery initiation were significantly greater than at baseline. The persistence and F/M amplitude ratio at 5-min after motor imagery initiation, however, was comparable to baseline levels.

CONCLUSION

Therefore, 1 to 3 min of motor imagery is likely sufficient to facilitate the excitability of spinal anterior horn cells.

Does the Improvement of Position Sense Following Motor Imagery Practice Vary as a Function of Age and Time of Day?

The effectiveness of motor imagery practice is known to depend on age and on the ability to form motor images. In the same individual, motor imagery quality changes during the day, being better late in the morning for older adults and in the afternoon for younger adults. Does this mean that motor imagery practice should be done at specific time of the day depending on the age of participants to maximize motor learning? To examine whether the effect of motor imagery practice varies as a function of time of day and age, the authors used an arm configuration reproduction task and measured position sense accuracy before and after 135 kinesthetic motor imagery trials. Younger and older participants were randomly assigned to either a morning or an afternoon session. Data showed that the accuracy for reproducing arm configurations improved following imagery practice regardless of time of day for both younger and older adults. Moreover, the authors observed that the position sense was less accurate in the afternoon than in the morning in older participants (before and after motor imagery practice), while performance did not change during the day in younger participants. These results may have practical implications in motor learning and functional rehabilitation programs. They highlight the effectiveness of motor imagery practice for movement accuracy in both younger and older adults regardless of time of day. By contrast, they reveal that the assessment of position sense requires that the time of day be taken into account when practitioners want to report on the older patients' progress without making any mistakes.

Subjective Vividness of Kinesthetic Motor Imagery Is Associated With the Similarity in Magnitude of Sensorimotor Event-Related Desynchronization Between Motor Execution and Motor Imagery

In the field of psychology, it has been well established that there are two types of motor imagery such as kinesthetic motor imagery (KMI) and visual motor imagery (VMI), and the subjective evaluation for vividness of motor imagery each differs across individuals. This study aimed to examine how the motor imagery ability assessed by the psychological scores is associated with the physiological measure using electroencephalogram (EEG) sensorimotor rhythm during KMI task. First, 20 healthy young individuals evaluated subjectively how vividly they can perform each of KMI and VMI by using the Kinesthetic and Visual Imagery Questionnaire (KVIQ). We assessed their motor imagery abilities by summing each of KMI and VMI scores in KVIQ (KMI_total and VMI_total). Second, in physiological experiments, they repeated two strengths (10 and 40% of maximal effort) of isometric voluntary wrist-dorsiflexion. Right after each contraction, they also performed its KMI. The scalp EEGs over the sensorimotor cortex were recorded during the tasks. The EEG power is known to decrease in the alpha-and-beta band (7–35 Hz) from resting state to performing state of voluntary contraction (VC) or motor imagery. This phenomenon is referred to as event-related desynchronization (ERD). For each strength of the tasks, we calculated the maximal peak of ERD during VC, and that during its KMI, and measured the degree of similarity (ERD_sim) between them. The results showed significant negative correlations between KMI_total and ERD_sim for both strengths (p < 0.05) (i.e., the higher the KMI_total, the smaller the ERD_sim). These findings suggest that in healthy individuals with higher motor imagery ability from a first-person perspective, KMI efficiently engages the shared cortical circuits corresponding with motor execution, including the sensorimotor cortex, with high compliance.

A functional limitation to the lower limbs affects the neural bases of motor imagery of gait

Studies on athletes or neurological patients with motor disorders have shown a close link between motor experience and motor imagery skills. Here we evaluated whether a functional limitation due to a musculoskeletal disorder has an impact on the ability to mentally rehearse the motor patterns of walking, an overlearned and highly automatic behaviour. We assessed the behavioural performance (measured through mental chronometry tasks) and the neural signatures of motor imagery of gait in patients with chronic knee arthrosis and in age-matched, healthy controls. During fMRI, participants observed (i) stationary or (ii) moving videos of a path in a park shown in the first-person perspective: they were asked to imagine themselves (i) standing on or (ii) walking along the path, as if the camera were “their own eyes” (gait imagery (GI) task). In half of the trials, participants performed a dynamic gait imagery (DGI) task by combining foot movements with GI. Behavioural tests revealed a lower degree of isochrony between imagined and performed walking in the patients, indicating impairment in the ability to mentally rehearse gait motor patterns. Moreover, fMRI showed widespread hypoactivation during GI in motor planning (premotor and parietal) brain regions, the brainstem, and the cerebellum. Crucially, the performance of DGI had a modulatory effect on the patients and enhanced activation of the posterior parietal, brainstem, and cerebellar regions that the healthy controls recruited during the GI task. These findings show that functional limitations of peripheral origin may impact on gait motor representations, providing a rationale for cognitive rehabilitation protocols in patients with gait disorders of orthopaedic nature. The DGI task may be a suitable tool in this respect.

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Patients with chronic knee arthrosis show impairment in gait motor imagery

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Impairment is selective for gait and paralleled by hypoactivation in premotor areas

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Peripheral limitation of lower limb movements affects central gait motor control

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Dynamic motor imagery favours the recruitment of a motor strategy during imagery

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Mental motor training might help to restore gait control in orthopaedic patients

Inhibition or facilitation? Modulation of corticospinal excitability during motor imagery

Motor imagery (MI) is the mental simulation of an action without any overt movement. Functional evidences show that brain activity during MI and motor execution (ME) largely overlaps. However, the role of the primary motor cortex (M1) during MI is controversial. Effective connectivity techniques show a facilitation on M1 during ME and an inhibition during MI, depending on whether an action should be performed or suppressed. Conversely, Transcranial Magnetic Stimulation (TMS) studies report facilitatory effects during both ME and MI. The present TMS study shed light on MI mechanisms, by manipulating the instructions given to the participants. In both Experimental and Control groups, participants were asked to mentally simulate a finger-thumb opposition task, but only the Experimental group received the explicit instruction to avoid any unwanted fingers movements. The amplitude of motor evoked potentials (MEPs) to TMS during MI was compared between the two groups. If the M1 facilitation actually pertains to MI per se, we should have expected to find it, irrespective of the instructions. Contrariwise, we found opposite results, showing facilitatory effects (increased MEPs amplitude) in the Control group and inhibitory effects (decreased MEPs amplitude) in the Experimental group. Control experiments demonstrated that the inhibitory effect was specific for the M1 contralateral to the hand performing the MI task and that the given instructions did not compromise the subjects' MI abilities. The present findings suggest a crucial role of motor inhibition when a "pure" MI task is performed and the subjects are explicitly instructed to avoid overt movements.