Medullary and spinal accessory nerve responses to vestibular stimulation

Responses to vestibular stimulation were recorded from the medullary, spinal, or both portions of the accessory nerve of decerebrate cats. The response consisted of a mixture of autonomic and somatic impulses, the latter particularly contributing to the size of the vestibular evoked activity. Dorsal root stimulation or ventroflexion of the neck strongly interfered with the spinal component of the response. The site of this proprioceptive, inhibitory action was mainly at the spinal level and only to a minor extent may have included supraspinal connections, via cerebellum and brainstem, acting upon the vestibular nuclear complex. The medullary or autonomic component of the accessory nerve response to vestibular stimulation was not under this inhibitory control. Thus, the stream of somatic impulses of importance for postural reflexes is constantly controlled and modified along the executive pathways, while autonomic impulses evoked by vestibular stimulation and given rise to the syndrome of motion sickness are not similarly influenced. The accessory nerves contain afferent fibers which cross the midline and make contact with the contralateral accessory nuclear complex but not with other motor cells within the ventral horn.