Tatsuya Hayami

The effects of kinesthetic illusory sensation induced by a visual stimulus on the corticomotor excitability of the leg muscles.

A novel method of visual stimulus, reported by Kaneko et al. [14], induced a vivid kinesthetic illusion and increased the corticomotor excitability of the finger muscles without any overt movement. To explore the effect of this method on the lower limbs, motor evoked potentials (MEP) were recorded from the left tibialis anterior (TA) and soleus muscles using transcranial magnetic stimulation (TMS). A computer screen that showed the moving image of an ankle movement was placed over the subjects leg, and its position was modulated to induce an illusory sensation that the subjects own ankle was moving (illusion condition). TMS was delivered at rest and at two different times during the illusion condition (ankle dorsiflexion phase: illusion-DF; ankle plantarflexion phase: illusion-PF). The MEP amplitude of the TA, which is the agonist muscle for ankle dorsiflexion, was significantly increased during the illusion-DF condition. This indicated that the visual stimulus showing the moving image of an ankle movement could induce a kinesthetic illusion and selectively increase the corticomotor excitability in an agonist muscle for an illusion, as was previously reported for an upper limb. The MEP amplitude of the soleus, which is the agonist muscle for ankle plantarflexion, increased during the illusion-PF condition, but not significantly. Because of the vividness of the illusory sensation was significantly greater during the illusion-DF condition than the illusion-PF condition, we concluded that the vividness of the illusory sensation had a crucial role in increasing corticomotor excitability.

Effect of kinesthetic illusion induced by visual stimulation on muscular output function after short-term immobilization

Kinesthetic illusions by visual stimulation (KiNVIS) enhances corticomotor excitability and activates motor association areas. The purpose of this study was to investigate the effect of KiNVIS induction on muscular output function after short-term immobilization. Thirty subjects were assigned to 3 groups: an immobilization group, with the left hand immobilized for 12h (immobilization period); an illusion group, with the left hand immobilized and additionally subjected to KiNVIS of the immobilized part during the immobilization period; and a control group with no manipulation. The maximum voluntary contraction (MVC), fluctuation of force (force fluctuation) during a force modulation task, and twitch force were measured both before (pre-test) and after (post-test) the immobilization period. Data were analyzed by performing two-way (TIME×GROUP) repeated measures ANOVA. The MVC decreased in the immobilization group only (pre-test; 37.8±6.1N, post-test; 32.8±6.9N, p<0.0005) after the immobilization period. The force fluctuation increased only in the immobilization group (pre-test; 2.19±0.54%, post-test; 2.78±0.87%, p=0.007) after the immobilization period. These results demonstrate that induction of KiNVIS prevents negative effect on MVC and force fluctuation after 12h of immobilization.

Evaluation of pulse height control for rapid isometric contractions in college sprinters

The ability of rapid force development is one of the important factors for improving physical performance. It has been known that rapid isometric force is controlled by a central motor program to maintain the rise time relatively constant independent of force amplitude (pulse height control). The advantage of using pulse height control is that it increases the rate of force with force amplitude. However, this strategy is believed to be applicable up to about 50–60% of maximal voluntary contractions (MVC). When the force level increases further, individuals often switch to pulse width control to increase the time to peak force. The aim of this study was to determine the force level (turning point) at which participants switch from pulse height control to pulse width control. This turning point was defined as the maximum force produced by pulse height control. We then attempted to examine whether this turning point is different among participants (control and sprinter groups). Therefore, participants were asked to perform isometric plantar flexions as fast as possible over a wide range of force levels (10–90%MVC). Our results showed that a turning point (%MVC) between two strategies was detected in all participants and the mean values were significantly higher in the sprinter group than that in the control group. Our results suggest that each participant has different limits of force level produced by pulse height control. The sprinter and control groups may use different control strategies for rapid force production at a higher force level.

The Long-Term Potentiation-Like Effect in the Corticomotor Area after Transcranial Direct Current Stimulation with Motor Imagery

The purpose of the present study was to clarify a long-term potentiation like effect in the corticomotor area after anodal transcranial direct current stimulation (tDCS), which had been done with motor imagery. Anodal tDCS was applied transcranially as an intervention to the left hand motor area in the right hemisphere for 15 min with the intensity of 1.0 mA during resting or motor imagery (MI) conditions. In the MI condition, subjects performed motor imagery of index finger abduction. Motor-evoked potentials (MEPs) were recorded from the first dorsal interossei (FDI) of the left hand before the intervention and at 0 min, 15 min, 30 min and 60 min after the intervention. The stimulus intensities of TMS were set at 1.05, 1.15, and 1.25 times the strength of the resting motor threshold (RMth). Increases of MEPs were detected with all intensities of TMS at 0 min and 15 min after tDCS with motor imagery. However, in the resting condition, MEP amplitudes were elevated only at 15 min after tDCS and at the highest TMS intensity of 1.25×RMth. The facilitatory effect induced by tDCS with motor imagery was significantly long-lasting and definite compared to that after tDCS without motor imagery.