Open access peer-reviewed chapter

Effectiveness of Motor Imagery on Physical Therapy: Neurophysiological Aspects of Motor Imagery

Written By

Yoshibumi Bunno

Submitted: April 29th, 2019 Reviewed: October 25th, 2019 Published: November 28th, 2019

DOI: 10.5772/intechopen.90277

From the Edited Volume

Physical Therapy Effectiveness

Edited by Mario Bernardo-Filho, Danúbiada Cunha de Sá-Caputo and Redha Taiar

Chapter metrics overview

726 Chapter Downloads

View Full Metrics

Abstract

Immediate enrollment in physical therapy and facilitation of the spinal motor neuron excitability are very important. We previously suggested that the F-wave parameters were significantly increased during motor imagery. Thus, motor imagery is a beneficial method to facilitate the spinal motor neuron excitability for patients with various motor dysfunctions. We also indicated that the imagined muscle contraction strength may not affect the spinal motor neuron excitability. Additionally, kinesthetic imagery can more facilitate the spinal motor neuron excitability; however, longer duration of motor imagery may decrease the spinal motor neuron excitability. Thus, when applying motor imagery to physical therapy, slight imagined muscle contraction strength may be sufficient to facilitate the spinal motor neuron excitability, and the duration and strategy of imagery should be considered.

Keywords

  • motor imagery
  • F-wave
  • muscle contraction strength
  • duration
  • strategy

1. Introduction

Motor imagery (MI) is the mental representation of a movement in the absence of any actual overt movement. It is a cognitive process creating specific motor actions within the working memory [1]. MI may be a beneficial tool to improve various motor functions for patients with stroke-induced motor deficits [2, 3, 4, 5]. Decline of motor evoked potential (MEP) amplitude, an index of corticospinal excitability obtained when transcranial magnetic stimulation is applied to the primary motor cortex, can be observed post-stroke [6]. Additionally, a significant reduction of spinal motor neuron excitability has been shown in the post-stroke acute phase [7]. Thus, corticospinal excitability, including that of spinal motor neurons, would be reduced post-stroke. Corticospinal excitability is considered to be an index of functional motor recovery [8], and immediate enrollment in rehabilitation for stimulation of corticospinal and spinal motor neuron excitability may be important to achieve better outcomes.

Neuroimaging studies show that MI activates motor-related brain regions, including the primary motor cortex, supplementary motor area, premotor area, prefrontal cortex, somatosensory area, parietal lobe, cingulate gyrus, cerebellum, and basal ganglia [9, 10]. Similarly, these regions have been shown as activated during motor execution [9, 10]. Furthermore, the MEP amplitude was shown as significantly increased during MI [11, 12, 13]. Thus, MI may stimulate the central nervous system. Various patterns of spinal motor neuron excitability have been observed during MI [14, 15, 16]. The F-wave is one of the indices of spinal motor neuron excitability. It is a compound action potential resulting from re-excitation (backfiring) at spinal anterior horn cells by an antidromic impulse following the distal electrical stimulation of motor nerve fibers [17, 18, 19]. The F-wave amplitude increases when the corticospinal descending volley collides with the antidromic peripheral volley [20]. Additionally, the F-wave is a reliable index of spinal motor neuron excitability, even when motor output is extremely low, as is the case during MI [21].

As described previously in this chapter, stimulating spinal motor neuron excitability would improve motor function. Our final goal is to find the most beneficial approach by which MI can increase the spinal motor neuron excitability. In the following sections, we introduce our research on spinal motor neuron excitability under various MI conditions. At the end of the chapter, we discuss the application of MI to physical therapy from a neurophysiological perspective.

Advertisement

2. The spinal motor neuron excitability during MI under different imagined muscle contraction strengths

2.1. Purpose

We previously reported that the spinal motor neuron excitability increased significantly when participants performed MI of isometric thenar muscle activity under 50% maximal voluntary contraction (MVC) [22]. However, it was unclear whether the magnitude of the imagined muscle contraction strength affects the spinal motor neuron excitability. Therefore, we used F-wave measurements to investigate the spinal motor neuron excitability during MI of isometric thenar muscle activity under various imagined muscle contraction strengths. Specifically, we adopted the 10, 30, 50, 70, and 100% MVC for imagined muscle contraction strength [23, 24, 25].

2.2. Materials

We conducted two experiments to assess the spinal motor neuron excitability during MI under different imagined muscle contraction strengths. Firstly, we measured the F-wave during MI under 10, 30, 50, and 70% MVC for 10 healthy volunteers (5 males, 5 females; mean age = 28.7 ± 4.5 years). Secondly, we measured the F-wave during MI under 50 and 100% MVC for 15 healthy volunteers (13 males, 2 females; mean age = 25.3 ± 5.0 years). All participants provided informed consent before study commencement. This research was approved by the Research Ethics Committee at Kansai University of Health Sciences. All recordings were conducted in accordance with the Declaration of Helsinki.

2.3. Methods

A Viking Quest electromyography (EMG) machine ver. 9.0 (Natus Medical Inc., USA) was used for the F-wave recording. A pair of silver disc electrodes (10 mm diameter, Natus Medical Inc., USA) were placed over left thenar eminence and base of the first dorsal metacarpal bone. The skin was cleaned with an abrasive gel, and then impedance was maintained below 5 kΩ. The F-wave was evoked from the left thenar muscles by delivering supramaximal electrical stimuli, 0.2 ms in duration and 0.5 Hz in frequency, to the median nerve at the left wrist. Supramaximal stimuli were determined 20% higher than the maximal stimulus intensity required to elicit the largest compound muscle action potential (M-wave). The sensitivity for the F-wave was set at 200 μV/division and a sweep of 5 ms/division. The bandwidth filter range was 20 Hz–3 kHz.

Participants were placed in the supine posture on a bed and instructed to fix their eyes on the display of a pinch meter (Digital Indicator F304A, Unipulse Corp., Japan) throughout the F-wave recording. To determine the baseline of spinal motor neuron excitability, the F-wave was measured during relaxation for 1 min (rest). Thereafter, participants exerted isometric left thenar muscle contraction at 50% MVC (i.e., participants pressed the sensor of the pinch meter using their thumb and index finger at 50% MVC) for 1 min with visual feedback. For the MI trial, participants performed MI of isometric thenar muscle activity under 50% MVC for 1 min (50% MI). Immediately after the 50% MI trial, the F-wave was recorded during relaxation for 1 min (post). There were 30 supramaximal electrical stimuli delivered during each trial for the F-wave recording. The above process was defined as the MI at 50% MVC condition (50% MI condition). This protocol was repeated for conditions of 10, 30, 70, and 100% MI. Each condition was performed randomly on different days.

2.4. F-wave data analysis

All measured F-wave data were analyzed with respect to two parameters: persistence and the F/M amplitude ratio. The minimum F-wave peak-to-peak amplitude was 20 μV [26]. The persistence was represented as the percentage of detected F-wave responses out of 30 supramaximal electrical stimuli. It reflects the number of backfiring spinal anterior horn cells [17, 19]. The F/M amplitude ratio was obtained as the mean of the ratios of each detected F-wave response amplitude divided by the corresponding M-wave amplitude; it reflects the number of backfiring spinal anterior horn cells and individual spinal anterior horn cell excitability [19]. Therefore, the persistence and F/M amplitude ratio are considered indices of spinal motor neuron excitability.

2.5. Statistical analysis

2.5.1. The F-wave during MI under 10, 30, 50, and 70% MVC

Because the Shapiro-Wilk test did not confirm the normality of the F-wave data, a nonparametric method was used for statistical analysis. The persistence and F/M amplitude ratio among the three trials (rest, MI, and post) under each MI condition (10, 30, 50, and 70% MI) were compared using the Friedman test and Scheffe’s post hoc test.

We also calculated the relative value obtained by dividing the F-wave data during MI under the four MI conditions by that at rest and compared the results using the Friedman test. SPSS Statistics ver. 19 software (IBM Corp., USA) was used for statistical analysis. The threshold for statistical significance was set at p < 0.05.

2.5.2. The F-wave during MI under 50 and 100% MVC

The persistence and F/M amplitude ratio among three trials (rest, MI, and post) under each MVC MI conditions were compared using the Friedman test and Scheffe’s post hoc test. The relative values between the two MI conditions were compared using the Wilcoxon signed rank test.

2.6. Results

2.6.1. The F-wave during MI under 10, 30, 50, and 70% MVC

The persistence during MI under all MI conditions was significantly higher than that at rest (10% MI vs. rest and 70% MI vs. rest, p < 0.01; 30% MI vs. rest and 50% MI vs. rest, p < 0.05) ( Tables 1 4 ). The F/M amplitude ratio during MI under 10, 30, and 50% MI conditions was significantly higher than that at rest (10% MI vs. rest and 50% MI vs. rest, p < 0.01; 30% MI vs. rest, p < 0.05) ( Tables 1 3 ). The F/M amplitude ratio during MI under the 70% MI condition tended to be more increased than that at rest (p = 0.082) ( Table 4 ). The F/M amplitude ratio immediately after MI under all MI conditions was reduced to the rest level ( Tables 1 4 ).

Table 1.

The F-wave under 10% MI condition.

Table 2.

The F-wave under 30% MI condition.

Table 3.

The F-wave under 50% MI condition.

Table 4.

The F-wave under 70% MI condition.

The relative values of the persistence and F/M amplitude ratio did not show significant differences among all MI conditions ( Table 5 ).

Table 5.

Relative values of the F-wave under 10% MI, 30% MI, 50% MI, and 70% MI condition.

2.6.2. The F-wave during MI under 50 and 100% MVC

The persistence during MI under the 50% MI and 100% MI conditions was significantly higher than that at rest (50% MI vs. rest and 100% MI vs. rest, p < 0.01; Tables 6 and 7 ), and the F/M amplitude ratio during MI under 50% and 100% MI conditions was significantly higher than that at rest (50% MI vs. rest and 100% MI vs. rest, p < 0.01; Tables 6 and 7 ). The F/M amplitude ratio immediately after MI (at post) under the 50% and 100% MI conditions did not show any significant differences compared with that at rest ( Tables 6 and 7 ).

Table 6.

The F-wave under 50% MI condition.

Table 7.

The F-wave under 100% MI condition.

The relative values of the persistence and F/M amplitude ratio did not show significant differences between two MI conditions ( Table 8 ).

Table 8.

Relative values of the F-wave under 50% MI and 100% MI condition.

2.7. Discussion

2.7.1. The spinal motor neuron excitability during MI of isometric thenar muscle activity

Both the persistence and the F/M amplitude ratio were significantly increased during MI under 10, 30, 50, 70, and 100% MVC. Previous research has demonstrated that the activation of various brain regions contributes to motor preparation and planning during MI [9, 10]. Thus, it is considered that the activation of the central nervous system that contributes to motor preparation and planning during MI is responsible for the observed increase in spinal motor neuron excitability via the descending pathways, such as the corticospinal and extrapyramidal tracts.

Furthermore, all participants in our previous studies performed MI while holding the sensor of the pinch meter. Mizuguchi et al. [27] reported that while holding an object, the corticospinal excitability during MI was modulated by a combination of tactile and proprioceptive inputs. Thus, it is plausible that holding the pinch meter sensor during MI caused tactile and proprioceptive perceptions to cooperatively increase the spinal motor neuron excitability along with the MI-activated pathways.

2.7.2. The spinal motor neuron excitability during MI under different imagined muscle contraction strengths

Relative values of the persistence and F/M amplitude were similar among all MI conditions. This result indicated that the magnitude of imagined muscle contraction strength may not affect spinal motor neuron excitability. Bonnet et al. [28] reported that the H-reflex amplitude during MI was similar between 2 and 10% MI conditions. Hale et al. [29] also reported that the H-reflex amplitude during MI of ankle plantar flexion was similar among five (i.e., 20, 40, 60, 80, and 100% MVC) MI conditions. Similarly, Aoyama and Kaneko [30] reported that the H-reflex amplitude during MI was similar between 50 and 100% MI conditions. MI is the mental representation of a movement in the absence of any overt movement [1]. The neural mechanism that inhibits actual movement and muscle contraction during MI may be involved in this result. Park et al. [31] reported that the MEP amplitude during MI was similar among all six (i.e., 10, 20, 30, 40, 50, and 60% MVC) MI conditions. Furthermore, the magnitude of primary motor cortex activity during MI did not correlate with that of the imagined muscle contraction strength, although the activities of the supplementary motor and premotor area during MI were strongly correlated with it [32]. The supplementary motor and premotor areas play crucial roles in larger force generation [33], motor planning, preparation, and inhibition [34, 35]. Thus, these areas may inhibit the actual muscle contraction depending on the magnitude of the muscle contraction strength. These areas are also directly connected to the primary motor cortex, and inhibitory inputs from them may suppress additional primary motor cortex excitation conferred by MI with high imagined contraction strengths. Therefore, the degree of spinal motor neuron excitability during MI at various imagined muscle contraction strengths may be modulated by both excitatory and inhibitory inputs from the central nervous system.

2.8. Conclusion

Our previous research has shown significant facilitation of the spinal motor neuron excitability during MI of isometric thenar muscle activity. The imagined muscle contraction strength may not be affected by the spinal motor neuron excitability. Thus, MI of isometric thenar muscle activity under slight MVC (i.e., 10% MVC) could substantially facilitate the spinal motor neuron excitability.

Advertisement

3. Does the duration of motor imagery affect the spinal motor neuron excitability?

3.1. Purpose

We previously reported that MI can increase the spinal motor neuron excitability and that the magnitude of imagined muscle contraction strength may not affect spinal motor neuron excitability [23, 24, 25]. In these studies, the duration of each MI session was 1 min. Driskell et al. [36] suggested that longer MI sessions do not always prove beneficial; they recommended a duration of approximately 20 min for an MI training session. Another study suggested that MI for 10–15 min elicited the most significant effect on performance [37]. Moreover, Twinning et al. [38] suggested that 5 min is the temporal limit beyond which it is difficult to concentrate and perform MI. As described previously, stimulation of spinal motor neuron excitability may be important for post-stroke rehabilitation; however, time-dependent changes in spinal motor neuron excitability during MI have not yet been investigated. Additionally, MI ability has a significant effect on brain activation [39] and corticospinal excitability [40]. In this study, we used F-waves to investigate whether the duration of MI and MI ability affects the spinal motor neuron excitability [41].

3.2. Materials

Eleven healthy volunteers participated in this research (8 males, 3 females, mean age = 26.4 ± 6.0 years). All participants gave written informed consent before study commencement. The study was approved by the Research Ethics Committee at the Graduate School of Kansai University of Health Sciences. All recordings were conducted in accordance with the Declaration of Helsinki.

3.3. Methods

The environment and F-wave recording conditions were set as previously described [23, 24, 25]. For the rest trial (rest), the F-wave was measured during relaxation for 1 min. Subsequently, participants learned the isometric thenar muscle activity at 50% MVC for 1 min with visual feedback. For the MI trial, participants performed the MI of isometric thenar muscle activity under 50% MVC for 5 min. F-waves were measured at 1, 3, and 5 min after the beginning of MI (1-, 3-, and 5-min MI, respectively). Immediately after MI, the F-wave was measured again during relaxation (post). After F-wave recordings, participants were asked to evaluate their vividness of MI, how vividly they could imagine isometric thenar muscle activity at 50% MVC, at 1, 3, and 5-min using a seven-point Likert scale ranging from 1 (very difficult to perform MI vividly) to 7 (very easy to perform MI vividly).

Background electromyography (EMG) was recorded using telemetry EMG (MQ-8, Kissei Comtec Co., Ltd., Japan) and EMG recording software (Vital Recorder 2, Kissei Comtec Co., Ltd.). Surface EMG signals were recorded for 5 min from the left thenar muscles to confirm no muscle contractions during MI. A pair of disposable Ag/AgCl electrodes (Blue Sensor N-00-S, Ambu A/S, Denmark) were placed over the muscle surface with an inter-electrode distance of 20 mm. EMG signals were recorded at rest; at 1, 3, and 5 min of MI; and post-trial. The recorded EMG data were analyzed using a multi-purpose biological information analysis system (BIMUTAS-Video, Kissei Comtec Co., Ltd.) after analog to digital conversion at a sampling frequency of 1 kHz. The root mean square values of the EMG data in each trial were then calculated.

3.4. Statistical analysis

We used a nonparametric method because the normality of F-wave data was not confirmed using the Shapiro-Wilk test. The persistence and F/M amplitude ratio among five trials (rest, 1, 3, 5-min MI, and post, respectively) were compared using the Friedman test and Scheffe’s post hoc test. The rating scores of MI vividness at 1, 3, and 5-min MI were compared using the Friedman test and Scheffe’s post hoc test. The SPSS statistics ver. 19 (IBM Corp., USA) was used for statistical analysis. The threshold for statistical significance was set at p = 0.05.

3.5. Results

In Figure 1 it is possible to verify that persistence and F/M amplitude ratio were significantly facilitated until 3 min from the beginning of MI task.

Figure 1.

Changes in persistence and F/M amplitude ratio during MI for 5 min (*p < 0.05, **p < 0.01). The persistence at 1 and 3 min MI was significantly higher than that at rest. The F/M amplitude ratio at 1 and 3 min MI was significantly higher than that at rest. Additionally, the F/M amplitude ratio at 5 min MI was significantly smaller than that at 1 and 3 min MI.

The score of MI vividness at 5-min MI was significantly decreased compared to 1-min MI (*p < 0.05; Table 9 ).

Table 9.

Rating scores of MI vividness at 1-min MI, 3-min MI, and 5-min MI.

There were no significant differences in the RMS data among five trials, and thus there was no measurable muscle activity during MI for 5 min.

3.6. Discussion

Both persistence and F/M amplitude ratio were significantly higher until 3 min from the beginning of MI. This result may suggest that participants could perform MI for at least 3 min without much difficulty. However, there were no significant differences in persistence and F/M amplitude ratio between the at rest and 5-min MI conditions. Additionally, the F/M amplitude ratio for the 5-min MI conditions was significantly lower than that for 1- and 3-min conditions. These findings may be due to mental fatigue; in one study, mental fatigue was found to have altered the maximal force production of the elbow flexor [42]. It also made it difficult for participants to maintain their focus on imagined movement [43]. Furthermore, repetitive MI of a handgrip movement decreased the MEP amplitude more than that at rest [44]. Thus, mental fatigue caused by sustained mental activity may have induced a decline of the spinal motor neuron excitability.

Furthermore, a decline of spinal motor neuron excitability can be also explained by MI habituation. MI is closely related to attentional processing [45]. Brain activation decreases by habituation after performing a cognitive motor task for 10 min. Furthermore, the corticospinal excitability was also decreased by habituation [46]. Specifically, brain activity showed an increase at 2 min before the onset of the task; however, after 4–6 min, activity decreased. Additionally, at the spinal level, the T-reflex amplitude, another index of the spinal motor neuron excitability, was significantly decreased due to habituation following sustained mental work for 20 min [47]. Our results also seemed to indicate that habituation to MI might occur approximately 4 min after its initiation and suggested that longer excitation times during MI might not be required for habituation of the central nervous system and spinal motor neurons.

Finally, practice time and MI ability were considered as possible factors affecting spinal motor neuron excitability. Regarding clinical use of MI for motor skill learning, Twining et al. [38] indicated that participants found it difficult to concentrate and perform MI for more than 5 min. Mental chronometry measured similar times for actual performance and MI [48]. Specifically, participants experienced difficulties in performing MI accurately beyond the practice time. In our study, the practice time for the motor task was only 1 min; thus, 1 min of practice time may be insufficient to continue performing MI for 5 min. Indeed, the vividness of MI tended to decrease with MI time. Furthermore, the vividness of MI at 5 min post MI initiation was significantly decreased relative to that at 1 min post MI initiation.

3.7. Conclusion

The persistence and F/M amplitudes at 1- and 3-min MI were significantly increased; however, the persistence and the F/M amplitude ratio at 5-min MI were reduced to rest levels. Thus, MI for 1–3 min may positively affect the spinal motor neuron excitability. In physical therapy, the duration of MI should be considered. As described in the Discussion section, matching the time of task practice to that of MI might be important. However, in this study, we did not investigate time-dependent changes of the spinal motor neuron excitability after motor learning for 5 min. Therefore, further research is required to resolve this issue. A limitation of this research is that differences in the brain activity during MI under 10, 30, 50, 70, and 100% MVC were not evaluated. Further study would be required to resolve this issue.

Advertisement

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

4.1. Purpose

Previous research has demonstrated that MI increases the spinal motor neuron excitability and that the magnitude of imagined contraction strength may not affect it [23, 24, 25]. Additionally, the duration of MI should be considered in physical therapy [41].

MI includes various components of perception that can be associated with actual movement [49], which is why the effects of MI may differ depending on the choice of sensory modality. Here, we used F-wave and MI ability to investigate whether the choice of imagery strategy affects the spinal motor neuron excitability [50].

4.2. Materials

Fourteen healthy volunteers participated in this research (10 males, 4 females, mean age = 23.4 ± 4.8 years). All participants gave written informed consent before study commencement. The study was approved by the Research Ethics Committee at the Graduate School of Kansai University of Health Sciences. All recordings were conducted in accordance with the Declaration of Helsinki.

4.3. Methods

The environment and F-wave recording conditions were set as previously described [23, 24, 25, 41]. To determine the baseline of the spinal motor neuron excitability, the F-wave was measured during relaxation for 1 min (rest). Subsequently, participants exerted isometric left thenar muscle contraction at 50% MVC for 1 min with visual feedback. Simultaneously, participants were instructed to learn the two imagery strategies: somatosensory (tactile and pressure perception of thumb finger pulp during pressing of the sensor of the pinch meter) and kinesthetic (thenar muscle contraction during pressing of the sensor of the pinch meter at 50% MVC). After learning each imagery strategy, participants performed somatosensory imagery (SI), kinesthetic imagery (KI), and combined somatosensory and kinesthetic imagery (SKI) randomly for 1 min. In SKI trial, participants performed kinesthetic and somatosensory imagery simultaneously. After all the F-wave recording, participants were asked to evaluate difficulty of each imagery strategies by using a 5-point Likert scale, ranging from 1 (very hard to image vividly) to 5 (very easy to image vividly).

Background electromyography (EMG) was recorded during rest and three imagery trials.

4.4. Statistical analysis

We used a nonparametric method because the normality of F-wave data was not confirmed using the Shapiro-Wilk test. The persistence and F/M amplitude ratio among four trials (rest, SI, KI, and SKI, respectively) were compared using the Friedman test and Scheffe’s post hoc test. The rating scores of each imagery strategies (SI, KI, and SKI, respectively) were compared using the Friedman test and Scheffe’s post hoc test. The background EMG data were compared using the Friedman test. The SPSS statistics ver. 19 (IBM Corp., USA) was used for statistical analysis. The threshold for statistical significance was set at p = 0.05.

4.5. Results

The persistence during SI and KI were significantly higher than that at rest (**p < 0.01; Figure 2 ). The persistence during SKI was tended to be increased than that at rest (p = 0.097; Figure 2 ). The F/M amplitude ratio during KI was significantly higher than that at rest (*p < 0.05; Figure 2 ).

Figure 2.

Changes in persistence and F/M amplitude ratio during SI, KI, and SKI (*p < 0.05, **p < 0.01). The persistence during SI and KI was significantly higher than that at rest. The persistence during SKI was tended to be increased than that at rest. The F/M amplitude ratio during KI was significantly higher than that at rest.

The rating score of SKI vividness was significantly lower than that at rest (*p < 0.05; Table 10 ).

Table 10.

Rating scores of MI vividness during SI, KI, and SKI.

There were no significant differences in the background EMG data among four trials (rest, SI, KI and SKI, respectively), and thus there was no measurable muscle contraction during three imagery trials.

4.6. Discussion

Both persistence and F/M amplitude ratio were significantly higher than the corresponding at-rest values. Previous neurophysiological studies reported that various regions of the brain related to motor functions were activated [9, 10] and that the MEP amplitude was significantly increased during KI [11, 13]. Thus, it seems that the central nervous system can better stimulate spinal motor neuron excitability via the descending pathways.

The persistence during SI was significantly higher than that at rest. This result was unexpected. We previously hypothesized that the spinal motor neuron excitability would remain unchanged because there are no motor-related factors in SI. Furthermore, there are no previous reports of tactile and proprioceptive perception SI increasing the corticospinal excitability including that of the primary motor cortex. Thus, it may be difficult to increase the spinal motor neuron excitability by SI. However, it is possible for SI to include kinesthetic components. Participants in this research were asked to imagine tactile and pressure perception while holding the pinch meter sensor between their thumb and index finger. Thus, they might have unintentionally imagined tactile and pressure perception along with thenar muscle activity.

The persistence during SKI tended to be increased as compared to that at rest. The rating score of SKI vividness was the lowest among the three imagery strategies. These results indicate that participants may not be able to perform SKI as vividly as the other two strategies. In this study, participants were required to pay attention to kinesthetic and somatosensory perceptions simultaneously. The decline in the amount of attention that can be allocated to each imagery strategy may have made it difficult for the participants to perform SKI vividly. Indeed, there was a positive correlation between the corticospinal excitability and MI vividness [40].

4.7. Conclusion

From the result of this research, KI may be a more effective imagery strategy, which can increase the spinal motor neuron excitability. Thus, the imagery strategy should be considered in physical therapy. Also, the spinal motor neuron excitability during SI was significantly increased. However, the mechanism that SI increases spinal motor neuron excitability is unclear. As a limitation of this research, we did not investigate brain activity during SI. Further research will be required to resolve this limitation.

Advertisement

5. How to use MI in physical therapy?

Our research indicates that MI of the isometric thenar muscle activity can increase spinal motor neuron excitability [22, 23, 24, 25, 41, 50]. After a stroke or a spinal cord injury, the excitability of the central nervous system decreases due to various factors, including the damage of neural substrates, loss of sensory inputs, and disuse of affected limbs [51]. Additionally, corticospinal excitability decreases following a decline in the size and number of corticospinal neurons [52]. Furthermore, decline of spinal motor neuron excitability was shown in the post-stroke acute phase [7, 53]. Thus, it may be important to stimulate corticospinal excitability, including that of the spinal motor neurons, as soon as possible. Patients in an early postoperative and post-stroke stage have difficulties in performing physical activities. However, considering the characteristics of MI, it can be a beneficial method to stimulate spinal motor neuron excitability without any overt movement and muscle contraction.

Furthermore, MI can improve not only the spinal motor neuron excitability but also various motor functions. Yue et al. [54] indicated that MI under 100% MVC for 4 weeks can increase the muscle strength of little finger abduction. Additionally, Sidaway et al. [55] indicated that MI under 100% MVC for 4 weeks can increase muscle strength of ankle dorsiflexion. About these results, Grosprêtre et al. [56] considered that MI may strengthen brain-to-muscle communication, including the enhanced recruitment of spinal motor neurons and involvement of the descending command. Although other groups [54, 55] adopted maximal imagined muscle contraction strengths for MI training, our results [23, 24, 25] revealed that the magnitude of imagined muscle contraction strength did not affect spinal motor neuron excitability. Thus, low (i.e., 10% MVC) imagined muscle contraction strengths might be sufficient for stimulation of spinal motor neuron excitability and muscle strength. Our research [25, 41, 50] also revealed that kinesthetic imagery can better stimulate spinal motor neuron excitability and that spinal motor neuron excitability remained higher than the at-rest value until 3 min after MI initiation. Therefore, to increase the effects of MI, kinesthetic perception should be chosen as the imagery strategy. Additionally, the duration of each MI session should be less than 3 min.

In conclusion, MI can increase the spinal motor neuron excitability, and its effect would be changed depending on the duration and strategy of imagery. Thus, the duration and strategy of imagery should be considered in clinical settings.

Advertisement

Acknowledgments

The author would like to thank Prof. Toshiaki Suzuki from Graduate school of Kansai University of Health Sciences for helpful comments on this manuscript.

Advertisement

Conflict of interest

There is no conflict of interest.

References

  1. 1. Guillot A, Di Rienzo F, Maclntyre T, Moran A, Collet C. Imagining is not doing but involves specific motor commands: A review of experimental data related to motor inhibition. Frontiers in Human Neuroscience. 2012;6:247. DOI: 10.3389/fnhum.2012.00247
  2. 2. Jackson PL, Lafleur MF, Malouin F, Richards C, Doyon J. Potential role of mental practice using motor imagery in neurologic rehabilitation. Archives of Physical Medicine and Rehabilitation. 2001;82:1133-1141. DOI: 10.1053/apmr.2001.24286
  3. 3. López ND, Monge Pereira E, Centeno EJ, Miangolarra Page JC. Motor imagery as a complementary technique for functional recovery after stroke: A systematic review. Topics in Stroke Rehabilitation. 2019;26:1-12. DOI: 10.1080/10749357.2019.1640000
  4. 4. Paolucci T, Cardarola A, Colonnelli P, Ferracuti G, Gonnella R, Murgia M, et al. Give me a kiss! An integrative rehabilitative training program with motor imagery and mirror therapy for recovery of facial palsy. European Journal of Physical and Rehabilitation Medicine. 2019. DOI: 10.23736/S1973-9087.19.05757-5
  5. 5. Kawasaki T, Tozawa R, Aramaki H. Effectiveness of using an unskilled model in action observation combined with motor imagery training for early motor learning in elderly people: A preliminary study. Somatosensory & Motor Research. 2018;35(3-4):204-211. DOI: 10.1080/08990220.2018.1527760
  6. 6. Foltys H, Krings T, Meister IG, Sparing R, Boroojerdi B, Thron A, et al. Motor representation in patients rapidly recovering after stroke: A functional magnetic resonance imaging and transcranial magnetic stimulation study. Clinical Neurophysiology. 2003;114(12):2404-2415. DOI: 10.1016/S1388-2457(03)00263-3
  7. 7. Drory VE, Neufeld MY, Korczyn AD. F-wave characteristics following acute and chronic upper motor neuron lesions. Electromyography and Clinical Neurophysiology. 1993;33(7):441-446
  8. 8. Triggs WJ, Calvanio R, Levine M. Transcranial magnetic stimulation reveals a hemispheric asymmetry correlate intermanual differences in motor performance. Neuropsychologia. 1997;35(10):1335-1363. DOI: 10.1016/S0028-3932(97)00077-8
  9. 9. Hanakawa T, Dimyan MA, Hallett M. Motor planning, imagery, and execution in the distributed motor network: A time-course study with functional MRI. Cerebral Cortex. 2008;18:2775-2788. DOI: 10.1093/cercor/bhn036
  10. 10. Hanakawa T. Organizing motor imageries. Neuroscience Research. 2016;104:56-63. DOI: 10.1016/j.neures.2015.11.003
  11. 11. Fourkas AD, Ionta S, Aglioti SM. Influence of imagined posture and imagery modality on corticospinal excitability. Behavioural Brain Research. 2006;168(2):190-196. DOI: 10.1016/j.bbr.2005.10.015
  12. 12. Fadiga L, Buccino G, Craighero L, Fogassi L, Gallese V, Pavesi G. Corticospinal excitability is specifically modulated by motor imagery: A magnetic stimulation study. Neuropsychologia. 1998;37(2):147-158. DOI: 10.1016/S0028-3932(98)00089-X
  13. 13. Stinear CM, Byblow WD. Modulation of corticospinal excitability and intracortical inhibition during motor imagery is task-dependent. Experimental Brain Research. 2004;157(3):351-358. DOI: 10.1007/s00221-004-1851-z
  14. 14. Taniguchi S, Kimura J, Yamada T, Ichikawa H, Hara M, Fujisawa R, et al. Effect of motion imagery to counter rest-induced suppression of F-wave as a measure of anterior horn cell excitability. Clinical Neurophysiology. 2008;119(6):1346-1352. DOI: 10.1016/j.clinph.2007.11.179
  15. 15. Kasai T, Kawai S, Kawanishi M, Yahagi S. Evidence for facilitation of motor evoked potentials (MEPs) induced by motor imagery. Brain Research. 1997;744(1):147-150. DOI: 10.1016/S0006-8993(96)01101-8
  16. 16. Oishi K, Kimura M, Yasukawa M, Yoneda T, Maeshima T. Amplitude reduction of H-reflex during mental movement simulation in elite athletes. Behavioural Brain Research. 1994;62(1):55-61. DOI: 10.1016/0166-4328(94)90037-X
  17. 17. Fisher MA. F-waves-physiology and clinical uses. The Scientific World Journal. 2007;7(1):144-160. DOI: 10.1100/tsw.2007.49
  18. 18. Kimura J. F-wave velocity in the central segment of the median and ulnar nerves. A study in normal subjects and in patients with Charcot-Marie-Tooth disease. Neurology. 1974;24(6):539-546. DOI: 10.1212/WNL.24.6.539
  19. 19. Mesrati F, Vecchierini MF. F-waves neurophysiology and clinical value. Neurophysiologie Clinique. 2004;34(5):217-243. DOI: 10.1016/j.neucli.2004.09.005
  20. 20. Mercuri B, Wassemann EM, Manqanotti P, Ikoma K, Samii A, Hallett M. Cortical modulation of spinal excitability: An F-wave study. Electroencephalography and Clinical Neurophysiology. 1996;101:16-24. DOI: 10.1016/0013-4694(95)00164-6
  21. 21. Rossini PM, Rossi S, Pasqualetti P, Tacchio F. Cortical excitability modulation to hand muscles during movement imagery. Cerebral Cortex. 1999;9:161-167. DOI: 10.1093/cercor/9.2.161
  22. 22. Suzuki T, Bunno Y, Onigata C, Tani M, Uragami S. Excitability of spinal neural function during several motor imagery tasks involving isometric opponens pollicis activity. NeuroRehabilitation. 2013;33(1):171-176. DOI: 10.3233/NRE-130942
  23. 23. Bunno Y, Yurugi Y, Onigata C, Suzuki T, Iwatsuki H. Influence of motor imagery of isometric opponens pollicis activity on the excitability of spinal motor neurons: A comparison using different muscle contraction strengths. Journal of Physical Therapy Science. 2014;26(7):1069-1073. DOI: 10.1589/jpts.26.1069
  24. 24. Bunno Y, Onigata C, Suzuki T. The imagined muscle contraction strengths did not affect the changes of spinal motor neurons excitability. Journal of Novel Physiotherapies. 2016;S3:008. DOI: 10.4172/2165-7025.S3-008
  25. 25. Bunno Y, Fukumoto Y, Todo M, Onigata C. The effect of motor imagery on spinal motor neuron excitability and its clinical use in physical therapy. In: Suzuki T, editor. Neurological Physical Therapy. Rijeka: IntechOpen; 2017. pp. 29-50. DOI: 10.5772/67471
  26. 26. Panayiotopoulos CP, Chroni E. F-waves in clinical neurophysiology: A review, methodological issues and overall value in peripheral neuropathies. Electroencephalography and Clinical Neurophysiology. 1996;101:365-374. DOI: 10.1016/0924-980X(96)95635-0
  27. 27. Mizuguchi N, Sakamoto M, Muraoka T, Nakagawa K, Kanazawa S, Nakata H, et al. The modulation of corticospinal excitability during motor imagery of action with objects. PLoS One. 2011;6(10):e26006. DOI: 10.1371/journal.pone.0026006
  28. 28. Bonnet M, Decety J, Jeannerod M, Requina J. Mental simulation of an action modulates the excitability of spinal reflex pathways in man. Cognitive Brain Research. 1997;5(3):221-228. DOI: 10.1016/S0926-6410(96)00072-9
  29. 29. Hale BS, Raglin JS, Koceja DM. Effect of mental imagery of a motor task on the Hoffmann reflex. Behavioural Brain Research. 2003;142(1-2):81-87. DOI: 10.1016/S0166-4328(02)00397-2
  30. 30. Aoyama T, Kaneko F. The effect of motor imagery on gain modulation of the spinal reflex. Brain Research. 2011;1372(1):41-48. DOI: 10.1016/j.brainres.2010.11.023
  31. 31. Park WH, Li S. No graded responses of finger muscles to TMS during motor imagery of isometric finger forces. Neuroscience Letters. 2011;494(3):255-259. DOI: 10.1016/j.neulet.2011.03.027
  32. 32. Romero DH, Lacourse MG, Lawrence KE, Schandler S, Cohen MJ. Event-related potentials as a function of movement parameter variations during motor imagery and isometric action. Behavioural Brain Research. 2000;117(1-2):83-96. DOI: 10.1016/S0166-4328(00)00297-7
  33. 33. Oda S, Shibata M, Moritani T. Force-dependent changes in movement-related cortical potentials. Journal of Electromyography and Kinesiology. 1996;6(4):247-252. DOI: 10.1016/S1050-6411(96)00010-7
  34. 34. Nakata H, Sakamoto K, Ferretti A, Perrucci MG, Gratta CD, Kakigi R, et al. Somato-motor inhibitory processing in humans: An event-related functional MRI study. Neuroimage. 2008;39(4):1858-1866. DOI: 10.1016/j.neuroimage.2007.10.041
  35. 35. Watanabe J, Sugiura M, Sato K, Sato Y, Maeda Y, Matsue Y, et al. The human prefrontal and parietal association cortices are involved in NO-GO performances: An event-related fMRI study. NeuroImage. 2002;17(3):1207-1216. DOI: 10.1006/nimg.2002.1198
  36. 36. Driskell J, Copper C, Moran A. Does mental practice enhance performance? Journal of Applied Psychology. 1994;79:481-492. DOI: 10.1037/0021-9010.79.4.481
  37. 37. Hinshaw KE. The effects of mental practice on motor skill performance: Critical evaluation and meta-analysis. Imagination, Cognition and Personality. 1991;11:3-35. DOI: 10.2190/X9BA-KJ68-07AN-QMJ8
  38. 38. Twining WE. Mental practice and physical practice in learning a motor skill. Research Quarterly. 1949;20:432-435
  39. 39. Lorey B, Pilqramm S, Bischoff M, Stark R, Vaitl D, Kindermann S, et al. Activation of the parieto-premotor network is associated with vivid motor imagery—A parametric fMRI study. PLoS One. 2011;6:e20368. DOI: 10.1371/journal.pone.0020368
  40. 40. Williams J, Pearce AJ, Loporto M, Morris T, Holmes PS. The relationship between corticospinal excitability during motor imagery and motor imagery ability. Behavioural Brain Research. 2012;226:369-375. DOI: 10.1016/j.bbr.2011.09.014
  41. 41. Bunno Y. Does the duration of motor imagery affect the excitability of spinal anterior horn cells? Somatosensory & Motor Research. 2018;35(3-4):223-228. DOI: 10.1080/08990220.2018.1538963
  42. 42. Bray SR, Graham JD, Martin Ginis KA, Hicks AL. Cognitive task performance causes impaired maximum force production in human hand flexor muscles. Biological Psychology. 2012;89:195-200. DOI: 10.1016/j.biopsycho.2011.10.008
  43. 43. Rozand V, Lebon F, Stapley PJ, Papaxanthis C, Lepers R. A prolonged motor imagery session alter imagined and actual movement durations: Potential implications for neurorehabilitation. Behavioural Brain Research. 2016;297:67-75. DOI: 10.1016/j.bbr.2015.09.036
  44. 44. Kluger BM, Palmer C, Shattuck JT, Triggs WJ. Motor evoked potential depression following repetitive central motor initiation. Experimental Brain Research. 2012;216:585-590. DOI: 10.1007/s00221-011-2962-y
  45. 45. Decety J. The neurophysiological basis of motor imagery. Behavioural Brain Research. 1996;77:45-52. DOI: 10.1016/0166-4328(95)00225-1
  46. 46. Tana MG, Montin E, Cerutti S, Bianchi AM. Exploring cortical attentional system by using fMRI during a Continuous Performance Test. Intelligence and Neuroscience. 2010:329213. DOI: 10.1155/2010/329213
  47. 47. Brunia CH, Zwaga HJ, van Boxtel A. Tendon reflex amplitude with increasing task difficulty. Ergonomics. 1973;16:495-499. DOI: 10.1080/00140137308924538
  48. 48. Guillot A, Collet C. Duration of mentally simulated movement: A review. Journal of Motor Behavior. 2005;37:10-20. DOI: 10.3200/JMBR.37.1.10-20
  49. 49. McNorgan C. A meta-analytic review of multisensory imagery identifies the neural correlates of modality-specific and modality-general imagery. Frontiers in Human Neuroscience. 2012;6:285. DOI: 10.3389/fnhum.2012.00285
  50. 50. Bunno Y. Imagery strategy affects spinal motor neuron excitability—Using kinesthetic and somatosensory imagery. Neuroreport. 2019;30(7):463-467. DOI: 10.1097/WNR.0000000000001218
  51. 51. Liepert J, Bauder H, Miltner WHR, Taub E, Weiller C. Treatment-induced cortical reorganization after stroke in humans. Stroke. 2000;31:1210-1216. DOI: 10.1161/01.STR.31.6.1210
  52. 52. Wrigley PJ, Gustin SM, Macey PM, Nash PG, Gandevia SC, Macefield VG, et al. Anatomical changes in human motor cortex and motor pathways following complete thoracic spinal cord injury. Cerebral Cortex. 2009;19:224-232. DOI: 10.1093/cercor/bhn072
  53. 53. Naseri M, Petramfar P, Ashraf A. Effect of motor imagery on the F-wave parameters in hemiparetic stroke survivors. Annals of Rehabilitation Medicine. 2015;39:401-408. DOI: 10.5535/arm.2015.39.3.401
  54. 54. Yue G, Cole KJ. Strength increases from the motor program: Comparison of training with maximal voluntary and imagined muscle contractions. Journal of Neurophysiology. 1992;67(5):1114-1123. DOI: 10.1152/jn.1992.67.5.1114
  55. 55. Sidaway B, Trzaska AR. Can mental practice increase ankle dorsiflexor torque? Physical Therapy. 2005;85(10):1053-1060. DOI: 10.1093/ptj/85.10.1053
  56. 56. Grosprêtre S, Jacquet T, Lebon F, Papaxanthis C, Martin A. Neural mechanisms of strength increase after one week motor imagery training. European Journal of Sport Science. 2017;18(2):209-218. DOI: 10.1080/17461391.2017.1415377

Written By

Yoshibumi Bunno

Submitted: April 29th, 2019 Reviewed: October 25th, 2019 Published: November 28th, 2019