Comparison of the pain-relieving effects of transcutaneous electrical nerve stimulation applied at the same dermatome levels as the site of pain in the wrist joint.

[Purpose] The purpose of this study was to develop a proposal for an effective interventional option for therapeutic stimulation sites by comparing the pain-relieving effect of transcutaneous electrical nerve stimulation (TENS) applied to the same dermatome level of the contralateral sites of the dorsal wrist joint with the pain or the neck, or both sites simultaneously. [Subjects and Methods] A control was first established by triggering pain in the left dorsal wrist joints of adult females by using heat stimulation. Three interventions were then performed, comprising the TENS to the contralateral wrist joint (CW) and to the neck (N) at the same dermatome level as the site of pain, and the TENS to both CW and N simultaneously (CWN). Levels of pain and cerebral blood flow were also measured. [Results] The pain levels of three interventions were found to be significantly decreased compared with the control; however, no significant differences in the levels of pain were seen between any combinations of three interventions. Furthermore, no significant differences were seen between any interventions in terms of cerebral blood flow. [Conclusion] The results suggest that in order for TENS to be effective, it is necessary to make effective use of the dermatome.

Excitability changes in primary motor cortex just prior to voluntary muscle relaxation.

We postulated that primary motor cortex (M1) activity does not just decrease immediately prior to voluntary muscle relaxation; rather, it is dynamic and acts as an active cortical process. Thus we investigated the detailed time course of M1 excitability changes during muscle relaxation. Ten healthy participants performed a simple reaction time task. After the go signal, they rapidly terminated isometric abduction of the right index finger from a constant muscle force output of 20% of their maximal voluntary contraction force and performed voluntary muscle relaxation. Transcranial magnetic stimulation pulses were randomly delivered before and after the go signal, and motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous muscle. We selected the time course relative to an appropriate reference point, the onset of voluntary relaxation, to detect excitability changes in M1. MEP amplitude from 80 to 60 ms before the estimated electromyographic offset was significantly greater than that in other intervals. Dynamic excitability changes in M1 just prior to quick voluntary muscle relaxation indicate that cortical control of muscle relaxation is established through active processing and not by simple cessation of activity. The cortical mechanisms underlying muscle relaxation need to be reconsidered in light of such dynamics.

Hemispheric asymmetry of ipsilateral motor cortex activation in motor skill learning.

In this study, we investigated how ipsilateral motor cortex (M1) activation during unimanual hand movements and hemispheric asymmetry changed after motor skill learning. Eleven right-handed participants preformed a two-ball-rotation motor task with the right and the left hand, separately, in all experimental sessions. Before and after exercise sessions, the degree of ipsilateral M1 activation during brief execution of the motor task was measured as changes in the size of motor-evoked potentials (MEPs) of the thenar and the first dorsal interosseous muscle of the nontask hand using transcranial magnetic stimulation. Before exercise, MEPs of the nontask hand were significantly facilitated on both sides during the motor task. After exercise, facilitation of MEPs of the nontask hand during the motor task was significantly reduced for the right hand (thenar: P=0.014, first dorsal interosseous: P=0.022) but not for the left hand. We conclude that ipsilateral M1 activation, associated with a complex motor task, is first symmetrical in both hemispheres. However, on exercise, ipsilateral activation is reduced only in left M1, indicating a stronger learning-dependent modification of motor networks within the left hemisphere.

Affordance effects in grasping actions for graspable objects: electromyographic reaction time study.

It is unclear whether affordance effects shorten the reaction time in the interaction between objects and actions. This study investigated affordance effects based on compatibility between perception of graspable objects and the act of grasping. The electromyographic reaction time (EMG-RT) was used as the response, and Go/NoGo (Experiment 1) and choice (Experiment 2) reaction-time tasks were performed using combinations of two types of stimulus image (tools and animals) and two types of response task (flexion and extension of all fingers). In Experiment 1, no interaction of stimulus images and response tasks occurred, but the EMG-RT for tools was statistically significantly delayed longer than that for animals. In Experiment 2, the EMG-RT of flexion of all fingers for tools was statistically significantly delayed compared with that for animals, showing interaction. Affordance effects based on compatibility of objects and actions are the basis on human-tool interaction. This interaction induces a goal-directed act and prolongs motor execution of grasping actions for them.