周期的な複数肢協調運動の運動方向による制約の発現因子

早大学位記番号:新6528早稲田大

Corticospinal excitability modulation in resting digit muscles during cyclical movement of the digits of the ipsilateral limb

We investigated how corticospinal excitability of the resting digit muscles was modulated by the digit movement in the ipsilateral limb. Subjects performed cyclical extension-flexion movements of either the right toes or fingers. To determine whether corticospinal excitability of the resting digit muscles was modulated on the basis of movement direction or action coupling between ipsilateral digits, the right forearm was maintained in either the pronated or supinated position. During the movement, the motor evoked potential (MEP) elicited by transcranial magnetic stimulation was measured from either the resting right finger extensor and flexor, or toe extensor and flexor. For both finger and toe muscles, independent of forearm position, MEP amplitude of the flexor was greater during ipsilateral digit flexion as compared to extension, and MEP amplitude of the extensor was greater during ipsilateral digit extension as compared to flexion. An exception was that MEP amplitude of the toe flexor with the supinated forearm did not differ between during finger extension and flexion. These findings suggest that digit movement modulates corticospinal excitability of the digits of the ipsilateral limb such that the same action is preferred. Our results provide evidence for a better understanding of neural interactions between ipsilateral limbs, and may thus contribute to neurorehabilitation after a stroke or incomplete spinal cord injury

The Modulation of Corticospinal Excitability during Motor Imagery of Actions with Objects

We investigated whether corticospinal excitability during motor imagery of actions (the power or the pincer grip) with objects was influenced by actually touching objects (tactile input) and by the congruency of posture with the imagined action (proprioceptive input). Corticospinal excitability was assessed by monitoring motor evoked potentials (MEPs) in the first dorsal interosseous following transcranial magnetic stimulation over the motor cortex. MEPs were recorded during imagery of the power grip of a larger-sized ball (7 cm) or the pincer grip of a smaller-sized ball (3 cm)—with or without passively holding the larger-sized ball with the holding posture or the smaller-sized ball with the pinching posture. During imagery of the power grip, MEPs amplitude was increased only while the actual posture was the same as the imagined action (the holding posture). On the other hand, during imagery of the pincer grip while touching the ball, MEPs amplitude was enhanced in both postures. To examine the pure effect of touching (tactile input), we recorded MEPs during imagery of the power and pincer grip while touching various areas of an open palm with a flat foam pad. The MEPs amplitude was not affected by the palmer touching. These findings suggest that corticospinal excitability during imagery with an object is modulated by actually touching an object through the combination of tactile and proprioceptive inputs

A 100 W-Class Water-Vapor Hall Thruster for Constellations and Space Explorations by SmallSats

The laboratory models of a water-vapor Hall thruster and LaB6 thermionic cathode were developed and tested. To optimize the thruster design to water-vapor propellant, the geometrical investigation was conducted. After testing six different models, the smallest thruster, with an outer diameter of 20 mm, was found to be the most suitable for 100-W class operation. This thruster was able to be operated less than 100 W at 200 V. In addition, the discharge power was suppressed to 200 W even at 300 V. Based on the plume diagnostics, the thrust force of 2.9 mN, specific impulse of 650 s, and anode efficiency of 4.6 % were obtained as a representative performance of this 300 V operating point. After the thruster operation was achieved, the cathode coupling test was conducted to demonstrate electron emission under water-vapor plasma existence. As a result of this experiment, the effective increase in electron current compared to the previous stand-alone tests was confirmed as well as the compatability to the water-vapor plasma plume. On the other hand, the electron emission current has not achieved 100 mA-class yet and the required heating power was predicted over 100 W; thus, further improvement is progressing

Static magnetic field stimulation applied over the cervical spinal cord can decrease corticospinal excitability in finger muscle

Objective: Transcranial static magnetic field stimulation has recently been demonstrated to modulate cortical excitability. In the present study, we investigated the effect of transspinal static magnetic field stimulation (tsSMS) on excitability of the corticospinal tract. Methods: A compact magnet for tsSMS (0.45 Tesla) or a stainless steel cylinder for sham stimulation was positioned over the neck (C8 level) of 24 able-bodied subjects for 15 min. Using 120% of the resting motor threshold transcranial magnetic stimulation intensity, motor evoked potentials (MEPs) were measured from the first digital interosseous muscle before, during, and after the tsSMS or sham intervention. Results: Compared with baseline MEP amplitudes were decreased during tsSMS, but not during sham stimulation. Additionally, during the intervention, MEP amplitudes were lower with tsSMS than sham stimulation, although these effects did not last after the intervention ceased. Conclusions: The results suggest that static magnetic field stimulation of the spinal cord by a compact magnet can reduce the excitability of the corticospinal tract. Significance: Transspinal static magnetic field stimulation may be a new non-invasive neuromodulatory tool for spinal cord stimulation. Its suppressive effect may be applied to patients who have pathological hyperexcitability of the spinal neural network. Keywords: Static magnetic field, Spinal cord, Motor evoked potential, Neuromodulatio