Cervical myelopathy (CM) caused by spinal cord compression can lead to reduced hand dexterity. However, except for the 10 sec grip-and-release test, there is no objective assessment system for hand dexterity in patients with CM. Therefore, we evaluated the hand dexterity impairment of patients with CM objectively by asking them to perform a natural prehension movement. Twenty-three patients with CM and 30 age-matched controls were asked to reach for and grasp a small object with their right thumb and index finger and to subsequently lift and hold it. To examine the effects of tactile afferents from the fingers, objects with surface materials of differing textures (silk, suede, and sandpaper) were used. All patients also underwent the Japanese Orthopedic Association (JOA) test. Preoperative patients showed significantly greater grip aperture during reach-to-grasp movements and weaker grip force than controls only while attempting to lift the most slippery object (silk). Patients, immediately after surgery, (n = 15) tended to show improvements in the JOA score and in reaction time and movement time with respect to reaching movements. Multiple regression analysis demonstrated that some parameters of the prehension task could successfully predict subjective evaluations of dexterous hand movements based on JOA scores. These results suggest that quantitative assessments using prehension movements could be useful to objectively evaluate hand dexterity impairment in patients with CM.

It is unclear how descending inputs from the vestibular system affect the excitability of cervical interneurons in humans. To elucidate this, we investigated the effects of galvanic vestibular stimulation (GVS) on the spatial facilitation of motor-evoked potentials (MEPs) induced by combined pyramidal tract and peripheral nerve stimulation. To assess the spatial facilitation, electromyograms were recorded from the biceps brachii muscles (BB) of healthy subjects. Transcranial magnetic stimulation (TMS) over the contralateral primary motor cortex and electrical stimulation of the ipsilateral ulnar nerve at the wrist were delivered either separately or together, with interstimulus intervals of 10 ms (TMS behind). Anodal/cathodal GVS was randomly delivered with TMS and/or ulnar nerve stimulation. The combination of TMS and ulnar nerve stimulation facilitated BB MEPs significantly more than the algebraic summation of responses induced separately by TMS and ulnar nerve stimulation (i.e., spatial facilitation). MEP facilitation significantly increased when combined stimulation was delivered with GVS (p < 0.01). No significant differences were found between anodal and cathodal GVS. Furthermore, single motor unit recordings showed that the short-latency excitatory peak in peri-stimulus time histograms during combined stimulation increased significantly with GVS. The spatial facilitatory effects of combined stimulation with short interstimulus intervals (i.e., 10 ms) indicate that facilitation occurred at the premotoneuronal level in the cervical cord. The present findings therefore suggest that GVS facilitates the cervical interneuron system that integrates inputs from the pyramidal tract and peripheral nerves and excites motoneurons innervating the arm muscles.

[Purpose] Lower-limb deep vein thrombosis is a complication of orthopedic surgery. A leg-exercise apparatus named “LEX” was developed as a novel active-exercise apparatus for deep vein thrombosis prevention. Muscle activity was evaluated to assess the effectiveness of exercise with LEX in the prevention. [Subjects] Eight healthy volunteers participated in this study. [Methods] Muscle activities were determined through electromyography during exercise with LEX [LEX (+)] and during active ankle movements [LEX (−)]. The end points were peak % maximum voluntary contraction and % integrated electromyogram of rectus femoris, vastus lateralis, biceps femoris, tibialis anterior, gastrocnemius, and soleus. [Results] LEX (+) resulted in higher average values in all muscles except the tibialis anterior. Significant differences were noted in the peak of the biceps femoris and gastrocnemius and in the integrated electromyogram of the rectus femoris, vastus lateralis, gastrocnemius, and soleus. The LEX (+)/LEX (−) ratio of the peak was 2.2 for the biceps femoris and 2.0 for the gastrocnemius . The integrated electromyogram was 1.8 for the gastrocnemius, 1.5 for the rectus femoris, 1.4 for the vastus lateralis, and 1.2 for the soleus. [Conclusion] Higher muscle activity was observed with LEX (+). LEX might be a good tool for increasing lower-limb blood flow and deep vein thrombosis prevention.

In animal experiments, the indirect corticospinal tract (CST) system via cervical interneurons has been shown to mediate motor commands for online adjustment of visuomotor behaviors, such as target-reaching. However, it is still unclear whether the similar CST system functions to perform similar motor behaviors in humans. To clarify this, we investigated changes in motor-evoked potentials (MEPs) in the elbow muscles following transcranial magnetic stimulation, transcranial electrical stimulation, or cervicomedullary stimulation while participants executed target-reaching and switching movements. We found that the MEP, whether elicited cortically or subcortically, was modulated depending on the direction of the switching movements. MEP facilitation began around the onset of the switching activities in an agonist muscle. Furthermore, ulnar nerve-induced MEP facilitation, which could be mediated by presumed cervical interneuronal systems, also increased at the onset of MEP facilitation. In a patient with cortical hemianopsia who showed switching movements in the scotoma, the MEPs were facilitated just before the switching activities. Our findings suggested that CST excitation was flexibly tuned with the switching movement initiation, which could partly take place in the subcortical networks, including the presumed cervical interneuronal systems.

Modulatory actions of inputs from the visual system to cervical interneurons (IN) for arm muscle control are poorly understood in humans. In the present study, we examined whether visual stimulation modulates the excitation of cervical IN systems mediating corticospinal tract (CST) inputs to biceps brachii (BB). Twenty-eight healthy volunteers were seated and electromyogram recordings from the BB were performed across six experiments, each with discrete objectives. A flash stimulator for visual stimulation (50-μs duration) was placed 60 cm from the participant's eye. The CST was stimulated with transcranial magnetic/electrical stimulation (TMS/TES, respectively) contralateral to the recording site. Visual stimulation with TMS/TES was randomly delivered during weak tonic BB contractions. Single TMS/TES-induced motor-evoked potentials (MEPs) were markedly enhanced from 60-100 ms after visual stimulation compared with the control condition. The MEPs were significantly increased by combining the electrical stimulation of the ulnar nerve at the wrist [7.5-12 ms of nerve stimulation (NERVE)/TMS interval] with and without visual stimulation compared to the algebraic summation of responses obtained with either TMS or NERVE. Interestingly, the combined stimulation -induced MEP facilitation was significantly increased after visual stimulation compared with the control. Single motor unit (MU) recording also revealed the further enhancement of combined stimulation effects on the firing probabilities of MU during visual stimulation, which was observed in the peaks of the peri-stimulus time histogram, 1-2 ms later than the onset latency. The present findings suggest that visual stimulation facilitates the oligosynaptic CST excitation of arm motoneurons mediated by the cervical IN system.