AUTONOMIC REACTION TO VESTIBULAR DAMAGE

The vestibular system provides inputs to many neurons in the brain ste m that participate in autonomic control, This multiplicity of vestibul ar-autonomic connections plays a variety of roles. Whereas it has been known for decades that unilateral vestibular lesions can result in mo tion sickness, recent data suggest that the vestibular system particip ates in making adjustments in blood pressure and respiration that are necessary to maintain homeostasis during movement and changes in postu re, Animals with bilateral vestibular lesions are more susceptible to posturally related hypotension than vestibularly intact animals, and i t is also possible that orthostatic hypotension after space flight is caused in part by microgravity-related changes in otolith function. Pa tients with vestibular lesions could also be more vulnerable to respir atory disturbances related to posture, such as obstructive apnea. Vest ibular dysfunction has additionally been linked with anxiety disorders , such as agoraphobia, which may result from alteration of vestibular inputs to brain stem monoaminergic neurons (which are known to process these signals). Even sleep disturbances might be connected with vesti bular disorders because neurons in the pontine reticular formation tha t are critical in switching between sleep states may be influenced by labyrinthine inputs. Thus it is likely that vestibular damage will res ult in a number of parallel disturbances in autonomic function,