Positional nystagmus/vertigo with specific gravity differential between cupula and endolymph (buoyancy hypothesis)

Abstract

Transient positional nystagmus has been repeatedly observed following the ingestion of water- and lipid-soluble molecules with specific gravities differing from that of endolymph, such as alcohol or “heavy water”. The semicircular canals selectively transduce angular velocity and head acceleration, and under normal circumstances are insensitive to gravitational orientation and linear acceleration. A major reason for this insensitivity to head orientation in space is that the cupula and endolymph have the same specific gravity of 1.0087 relative to water (the sensory hair cells are embedded in the cupula which is housed in the ampulla of the canals). The neutral buoyancy of the cupula in the endolymph prevents any out-of-balance forces when linear accelerations are applied.