(p. 49) The Vestibulo-Autonomic System 

Many clinicians and scientists equate ‘vestibulo-autonomic responses’ with motion sickness. While motion sickness does include symptoms and signs such as pallor and cold sweating that result from the actions of the autonomic nervous system, considerable recent evidence shows that the vestibular system also participates in regulating blood distribution in the body and blood pressure during movement and changes in posture. This chapter reviews data collected in both animal and human subjects demonstrating the existence of vestibulo-sympathetic reflexes that act upon the cardiovascular system. This evidence shows that vestibulo-sympathetic responses are patterned, in that they differ between the upper and lower body. The neural pathways that mediate vestibulo-sympathetic responses are also described, which include projections from the caudal aspects of the medial and inferior vestibular nuclei to lateral regions of the caudal medullary reticular formation and the rostral ventrolateral medulla (RVLM). In turn, RVLM neurons relay vestibular signals to sympathetic preganglionic neurons in the thoracic spinal cord. Activity in this neural circuit is modulated by several brainstem regions, including nucleus tractus solitarius, the posterior cerebellar cortex, and likely others. Vestibulo-sympathetic responses are typically attenuated in conscious animals, and the gain of the responses appears to be modulated in accordance with ongoing behavioural activity. Finally, the clinical implications of vestibulo-sympathetic responses are discussed, as are the clinical symptoms that may result from dysfunction of the responses.