Effect of optokinetic stimulation on the H reflex in humans

We investigated the effects of optokinetic stimulation (OKS) on the soleus H reflex in ten healthy male subjects who were held in a fixed standing position. Upward and downward OKSs (60 degrees/s) were presented randomly. The H reflex amplitude decreased during upward OKSs and increased during downward ones (Kruskal-Wallis test, p < 0.02). Change in the H reflex amplitude was more marked during downward stimulation (p < 0.01). The H reflex was enhanced more during the acceleration phase of downward OKS than during the constant phase (p < 0.01), but it fluctuated during the former phase. These results suggest that OKS affects alpha motoneurone activity and that information from the visual system modulates the condition of the motor program at the spinal level.