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

From results of our previous works, it is suggested that MI of isometric thenar muscle activity at 10, 30, 50, 70, and 100% can facilitate the spinal motor neuron excitability. About this, it is considered to be influence of descending pathways corresponding to thenar muscle. Previous researches have demonstrated the activation of diverse brain area contribute to motor preparation and planning during MI [9–13]. The excitatory and inhibitory inputs modulate the spinal motor neuron excitability via the corticospinal and/or extrapyramidal tract [30]. Thus, it is plausibly that the activation of central nervous system contributes to motor preparation and planning during MI facilitated the spinal motor neuron excitability via the corticospinal and/or extrapyramidal tract.

Furthermore, all subjects participated in our previous works were instructed to perform MI with holding the sensor of a pinch meter. Mizuguchi et al. [31] reported that corticospinal excitability during MI utilizing an object was modulated by a combination of tactile and proprioceptive inputs while holding an object. We previously reported that the spinal motor neuron


Similarly, Aoyama and Kaneko [34] reported that the amplitude of H-reflex during MI was similar between 50% MI and 100% MI condition. In actual motion, the spinal motor neuron excitability was increased linearly with the muscle contraction strength [27]. Described in the introduction, MI is the mental rehearsal of a movement without any overt movement [1]. One possibility is the contribution of neural mechanism which inhibits actual movement and muscle contraction during MI. Park and Li [35] reported that the amplitude of MEPs during MI of finger flexion and extension at 10, 20, 30, 40, 50, and 60% MVC was significantly greater than that at rest. However, the amplitude of MEPs during MI was similar among all six MI conditions. Further, in an event-related potential study, the magnitude of primary motor cortex activity during MI did not correlate with the imagined muscle contraction strength, although activities of the supplementary motor and premotor area during MI were strongly correlated with it [36]. The supplementary motor and premotor area have crucial roles in larger force generation [37], motor planning, preparation, and inhibition [38, 39]. Thus, the supplementary motor and premotor area may inhibit the actual muscle activity depending on the muscle contraction strength. Because these areas also are connected directly to primary motor cortex, inhibitory inputs from the supplementary motor and premotor area may suppress any additional excitation of primary motor cortex conferred by MI with high imagined contraction strength. Furthermore, the spinal motor neuron excitability during MI is thought to be affected by central nervous system via the corticospinal and/or extrapyramidal tract. The degree of the spinal motor neuron excitability during MI at various imagined muscle contraction strengths may be modulated by both excitatory and inhibitory inputs

The Application of Motor Imagery to Neurorehabilitation

http://dx.doi.org/10.5772/intechopen.75411

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Our previous woks showed significant increase of the spinal motor neuron excitability during MI of isometric thenar muscle activity. However, the imagined muscle contraction strength

was not involved in change of the spinal motor neuron excitability.

**3. The autonomic nervous system during MI of isometric thenar** 

**3.1. The autonomic nervous system during MI of isometric thenar muscle activity at** 

We previously suggested that MI can facilitate the spinal motor neuron excitability. Sympathetic nerve activity was increased during actual isometric muscle contraction [41]. If MI shares common neural substrates with motor execution, it would be expected to observe the similar pattern in autonomic nervous system (ANS) activity during MI would be observed. In previous research, the heart rate during MI was significantly increased than that at rest [42]. Thus, MI can regulate sympathetic nerve activity without any overt movement. However, whether the imagined muscle contraction strength affects the ANS activity is still unclear.

from the central nervous system.

**2.4. Conclusion**

**muscle activity**

**10 and 50% MVC**

*3.1.1. Purpose*

**Table 6.** Changes in F-wave parameters under 50% MI condition.


**Table 7.** Changes in F-wave parameters under 100% MI condition.


**Table 8.** Comparison of F-wave parameters between 50% MI and 100% MI condition.

excitability during MI with holding the sensor of a pinch meter was significantly greater than that during MI without holding the sensor [20]. Consequently, it is suggested that tactile and proprioceptive perceptions during MI while holding the sensor facilitated the spinal motor neuron excitability cooperatively with MI-activated pathways.
