Noritaka Kawashima

Enhanced stretch reflex excitability in the soleus muscle during passive standing posture in humans

The purpose of this study was to test whether the spinal reflex excitability of the soleus muscle is modulated as posture changes from a supine to a passive upright position. Eight healthy subjects (29.6+/-5.4 yrs) participated in this study. Stretch and H-reflex responses were elicited while the subjects maintained passive standing (ST) and supine (SP) postures. The passive standing posture was accomplished by using a gait orthosis to which a custom-made device was mounted to elicit stretch reflex in the soleus muscle. This orthosis makes it possible to elicit stretch and H-reflexes without background muscle activity in the soleus muscle. The results revealed that the H-reflex amplitude in the ST was smaller than that in the SP condition, which is in good agreement with previous reports. On the other hand, the stretch reflex was significantly larger in the ST than in the SP condition. Since the experimental conditions of both the stretch and H-reflex measurements were exactly the same, the results were attributed to differences in the underlying neural mechanisms of the two reflex systems: different sensitivity of the presynaptic inhibition onto the spinal motoneuron pool and/or a change in the muscle spindle sensitivity.

Reconstruction and Tuning of Neural Circuits for Locomotion After Spinal Cord Injury

Because patients with an injured spinal cord face severe functional deficits, novel therapeutic approaches are required to treat this traumatic disorder. Recent advances in molecular biology and electrophysiology have rendered approaches based on these two subjects important in this field. A molecular approach involving tissue engineering is beneficial for preserving or restoring the neural circuit, i.e., the so-called hardware of the spinal cord. On the other hand, the electrophysiological approach has advantages such as modulation and analysis of use-dependent plastic changes in neural functioning of human subjects, which corresponds to the “software” of the spinal cord. Because varied biological processes are triggered after spinal cord injury, we should use either approach, or both, depending on the clinical problem that needs to be solved.