Semicircular Canal Function in Humans and Animals during Circular Walking

Abstract

It is generally accepted that the medial vestibulospinal tract originates in the medial vestibular nucleus, which is supplied from the semicircular canals. In animal studies of these pathways it descends only to the upper thoracic levels of the cord. In humans, however, there is some indirect evidence to support the concept that impulses from the semicircular canals reach the lumbosacral cord and influence lower as well as upper extremity activity. After unilateral horizontal duct stimulation with cold water, four-legged animals show deviation of the upper half of the body to the stimulated side. Under the same conditions, humans lose ipsilateral lower limb extensor tonus and tend to fall to the same side. It is logical to assume that the horizontal canal plays a role not only in passive but also in voluntary movements. Our observations demonstrate that the horizontal canal functions during circular walking so that the trunk is skillfully turned by the legs. In animals, the forelegs steer the body while the hindlegs advance it. However, in humans, the lower extremities perform both of these functions. The structure of the foot is wellsuited for these functions.