Shintaro Uehara

Task dependency of the long-latency facilitatory effect on the soleus H-reflex by cerebellar transcranial magnetic stimulation.

We investigated whether cerebellar transcranial magnetic stimulation (C-TMS) facilitates the excitability of the ipsilateral soleus motoneuron pool in resting humans, and whether the facilitation is modulated by a task that promotes cerebellar activity. A test tibial nerve stimulus evoking the H-reflex from the right soleus muscle was delivered before or after conditioning C-TMS in prone individuals. The amplitude of the H-reflex was significantly increased at conditioning-test interstimulus intervals of 110, 120, and 130 ms. Furthermore, we revealed that this facilitation effect was inhibited while the individuals tapped their right index finger. These findings indicate that C-TMS facilitates spinal motoneuronal excitability with an ∼100 ms latency in resting humans, and that this cerebellar spinal facilitation is modulated by a task that might increase cerebellar activity. Cerebellar spinal facilitation could thus be useful for assessing the excitability of the cerebellum, or the cerebellar output to spinal motoneurons.

Effect of cerebellar transcranial magnetic stimulation on soleus Ia presynaptic and reciprocal inhibition.

Previously, we reported that cerebellar transcranial magnetic stimulation (C-TMS) facilitates spinal motoneuronal excitability in resting humans. In this study, we aimed to characterize the descending pathway that is responsible for the C-TMS-associated cerebellar spinal facilitation. We evaluated the effect of C-TMS on ipsilateral soleus Ia presynaptic inhibition (PSI) and reciprocal inhibition (RI) because the vestibulospinal and reticulospinal tracts project from the cerebellum to mediate spinal motoneurons via interneurons associated with PSI. PSI and RI were measured with a soleus H-reflex test following operant conditioning using electrical stimulation of the common peroneal nerve. C-TMS was delivered before test tibial nerve stimulation with conditioning-test interstimulus intervals of 110 ms. C-TMS did not generate motor-evoked potentials, and it did not increase electromyography activity in the ipsilateral soleus muscle, indicating that C-TMS does not directly activate the corticospinal tract and motoneurons. However, C-TMS facilitated the ipsilateral soleus H-reflex and reduced the amount of soleus Ia PSI, but not RI. These findings indicate that C-TMS may facilitate the excitability of the spinal motoneuron pool via the vestibulospinal or reticulospinal tracts associated with PSI. Cerebellar spinal facilitation may be useful for assessing the functional connectivity of the cerebellum and vestibular nuclei or reticular formation.

After-effects of pedaling exercise on spinal excitability and spinal reciprocal inhibition in patients with chronic stroke.

Purpose of the study: To evaluate the after-effects of pedaling on spinal excitability and spinal reciprocal inhibition in patients with post-stroke spastic hemiparesis. Materials and methods: Twenty stroke patients with severe hemiparesis participated in this study and were instructed to perform 7 min of active pedaling and 7 min of passive pedaling with a recumbent ergometer at a comfortable speed. H reflexes and M waves of paretic soleus muscles were recorded at rest before, immediately after and 30 min after active and passive pedaling. The Hmax/Mmax ratio and H recruitment curve were measured. Reciprocal inhibition was assessed using the soleus H reflex conditioning test paradigm. Results: The Hmax/Mmax ratio was significantly decreased after active and passive pedaling exercise. The decreased Hmax/Mmax ratio after active pedaling lasted at least for 30 min. The H recruitment curve and reciprocal inhibition did not change significantly after active or passive pedaling exercise. Conclusions: Pedaling exercise decreased spinal excitability in patients with severe hemiparesis. Pedaling may be effective in rehabilitation following stroke.

Abnormal bias in subjective vertical perception in a post-stroke astasia patient

[Purpose] Post-stroke astasia is an inability to stand without external support despite having sufficient muscle strength. However, the dysfunction underlying astasia is unclear. We tested the hypothesis that astasia is the result of an abnormal bias in vertical perception, especially subjective postural vertical (SPV), mediated by somatosensory inputs. [Subjects and Methods] A patient with a right posterolateral thalamus hemorrhage had a tendency to fall toward the contralesional side during standing after 8 weeks of treatment. SPV, standing duration, and physical function were evaluated before and after a 1 week standard rehabilitation baseline period, and after a 1 week intervention period, where standing training requiring the patient to control his body orientation in reference to somatosensory inputs from his ipsilateral upper limb was added. [Results] SPV was biased toward the contralesional side before and after the 1 week baseline period. However, SPV improved into the normal range and he could stand for a longer duration after the intervention period. [Conclusion] This case suggests that abnormal SPV is one of the functional mechanisms underlying astasia, and it indicates the effectiveness of standing training with somatosensory information to improve abnormal SPV and postural disorders.

Motor control of downward object-transport movements with precision grip by object weight.

Abstract In the present study, we investigated the kinematics of object-transport movement in a downward direction using a precision grip, to elucidate how the central nervous system (CNS) takes into account object weight when making the movement, even when participants are unable to recognize the weight until they grasp the object. We found that the kinematics during transport movement were significantly changed by the object weight, even when the weight was unrecognized visually, suggesting that the CNS controls object-transport movement in a downward direction according to object weight, regardless of the visual recognizability of the weight.