Correlate diazeparn and meclizine's effects on the vestibular ocular reflex (VOR) with their ability to suppress motion sickness. Study design and methodology: Thirty subjects will have their vestibular (VOR gain, time constant, and reversal phase) and oculomotor function (gaze holding in the dark, OKN, and OKAN) tested at baseline and again two hours later. Immediately following the first set of tests the subject will ingest placebo, diazepam, meclizine, or nothing (randomized double blind order). After the second set of tests subjects will be exposed to a stimulus that promotes motion sickness. The subjects will make head movements while rotating at 120 deg/sec until they have reached a predetermined level of motion sickness defined by the Massachusetts Institute of Technology's modification of the Pensacola Diagnostic Index as Malaise III and note the number of head movements made until that point. Data will be examined for the correlation between the magnitude of the changes (with and without medication) of the VOR measurements and the difference in motion sickness susceptibility. The coefficients of a linear control system model of the vestibular and oculomotor systems will be manipulated to simulate the test results. The changes to the model may reflect functional localization of drug effects on the VOR, which may imply anatomical localization. Objectives: The vestibular system is a central component of both motion sickness and vestibular dizziness (vertigo) and both are treated with many of same medications including diazeparn and meclizine. Little is known, however, about their mechanisms of action in either motion sickness or vertigo. The objective of this study is to determine if diazeparn and meclizine's ability to prevent motion sickness is related to their ability to affect the VOR. This information is intended to help health care providers better treat patients with vertigo.
