Naoki Kado

Influence of Pacing by Periodic Auditory Stimuli on Movement Continuation: Comparison with Self-regulated Periodic Movement.

[Purpose] The purpose of this study was to investigate the influence of external pacing with periodic auditory stimuli on the control of periodic movement. [Subjects and Methods] Eighteen healthy subjects performed self-paced, synchronization-continuation, and syncopation-continuation tapping. Inter-onset intervals were 1,000, 2,000 and 5,000 ms. The variability of inter-tap intervals was compared between the different pacing conditions and between self-paced tapping and each continuation phase. [Results] There were no significant differences in the mean and standard deviation of the inter-tap interval between pacing conditions. For the 1,000 and 5,000 ms tasks, there were significant differences in the mean inter-tap interval following auditory pacing compared with self-pacing. For the 2,000 ms syncopation condition and 5,000 ms task, there were significant differences from self-pacing in the standard deviation of the inter-tap interval following auditory pacing. [Conclusion] These results suggest that the accuracy of periodic movement with intervals of 1,000 and 5,000 ms can be improved by the use of auditory pacing. However, the consistency of periodic movement is mainly dependent on the inherent skill of the individual; thus, improvement of consistency based on pacing is unlikely.

Effects of Practicing Difficult Movements of the Unilateral Arm on theExcitability of Spinal Motor Neurons in the Contralateral Arm

Background: The excitability of the spinal motor neurons of the contralateral upper limb increases during voluntary movement of the upper limbs. However, reports on the changes in the facilitation effects of the movements of the unilateral upper limb on the spinal motor neurons in the contralateral upper limb that are associated with motor learning are few. Methods: Sixteen right-handed healthy adults were randomly assigned to either the control group or the practice group. The F-waves were derived from the right abductor pollicis brevis muscle during the tasks before and after practice. The tasks included repetitive movements of the left upper limb between two small targets placed 20 cm apart on a desk. The subjects were instructed to accurately touch the targets with the tip of a pen. The practice of the practice group included repetitive movements using the same targets. The practice of the control group included repetitive movements without targets. The practice was performed for five sessions with each session consisting of 30 movements. The F-waves were analyzed for the amplitude ratio of F/M and latency. In addition, the number of times the tip of the pen touched the outside of the target was counted. Results: The amplitude ratio of F/M during post-practice significantly decreased compared with that during prepractice in the practice group. Latency showed no significant differences. The number of failures during post-practice decreased significantly compared with that during pre-practice in the practice group. Conclusion: This study suggests that the facilitation effects of the voluntary movements of the unilateral upper limb that were performed at a high difficulty level on the spinal motor neurons in the contralateral upper limb decreased with motor learning.

Effects of Repetitive Finger Movements on the Short-Latency Somatosensory-Evoked Potentials

When performing a movement, many features of sensory information are used as inputs and integrated. Smooth movement is possible by selecting necessary information from all‐sensory inputs. The somatosensory input of movement is adjusted at different levels such as at the level of the spinal cord, brainstem, and sensory cortex. However, sensory tests used by physical therapists provide only the sensory information that is perceiv‐ able through the parietal association fields. On the other hand, there is a somatosensory‐ evoked potentials (SEPs) in the tests of the somatic sensory function. An understanding of the SEPs enables the evaluation of the posterior track. Therefore, it is possible to deter‐ mine if the adjustment of somatosensory inputs occurs at any stage. The SEP amplitude is decreased by passive and voluntary movement. Further, characteristic decrease in the SEP amplitude is noted with an increase in the speed and intensity of movement. Thus, it is important for us to understand the relationship between motor tasks and somatosen‐ sory inputs. In this chapter, we introduce our study on the relationship between physi‐ cal movements and somatosensory inputs, and make recommendations for practicing physical therapy.

Influence of Auditory Pacing on the Control of Rhythmic Movement in Physical Therapy

The electromyographic reaction time data responses to various rhythm shifts are dis‐ cussed in Section 2 of this chapter. The following four experimental designs were intro‐ duced: (1) subliminal rhythm shift with shortened interval, (2) subliminal rhythm shift with lengthened interval, (3) subliminal rhythm shift with random interval, and (4) dif‐ ferences in the rate of rhythm shift. We found that the periodic rhythmic stimulation is predicted to comprise some time duration. Furthermore, the reactive movements can be performed without delay under conditions with an interstimulus‐onset interval shift of 7% of 1500 ms. When the physical therapist facilitates rhythmical reactive periodic movement using an external event such as a handclap, it will be desirable to keep the rhythm shift within 7% of the interstimulus‐onset interval. The variabilities of the inter‐ tap interval in the continuation paradigm of sensorimotor synchronization are discussed in Section 3. The participants performed self‐paced, synchronization‐continuation, and syncopation‐continuation tapping tasks. We found that the accuracy of the periodic movement with an interstimulus‐onset interval of 1000 ms can be improved by using auditory pacing. However, the consistency of periodic movement is mainly dependent on innate skill; thus, improvement in consistency from pacing alone is unlikely.

Relationship Between Excitability of Spinal Motor Neurons in Remote Muscles and Voluntary Movements

In physical therapy, it is important to understand the influence of the contraction of a particular muscle on other muscles. The mechanism of the facilitation effect of muscle contraction in healthy subjects has been analyzed in previous studies. These studies indicated that muscle contraction with voluntary movement enhances the excitability of spinal motor neurons and motor areas in the cerebral cortex that are not directly associ‐ ated with the contracting muscle. Furthermore, it has been reported that the facilitation effects on remote muscles not related to movement are affected by the elapsed time since the start of the movement, the strength of muscle contraction, the number of muscle spindles, and the difficulty of the movement. In addition, the facilitation effects of dif‐ ficult voluntary movements of the unilateral upper limbs on spinal motor neurons in the contralateral upper limb decrease with motor learning. We expect that these findings will be useful not only for physical therapy evaluation but also for patient treatment.