Caloric testing primarily assesses the function of which structure?

• A. Otolith organs
• B. Cochlea
• C. Vertical semicircular canal
• D. Horizontal semicircular canal

Answer: (D)

Caloric testing evaluates the vestibulo-ocular reflex by using temperature changes to drive endolymph movement in the semicircular canals. In the standard setup, the head is elevated so the horizontal canal is aligned with gravity, making it most responsive to the convection currents created by warm or cold irrigation. A warm stimulus causes increased firing on the treated side and nystagmus with fast phase away from that side; a cold stimulus does the opposite. Because gravity-driven flow most effectively stimulates the horizontal canal, caloric testing is primarily used to assess its function. The otolith organs respond to linear acceleration and head tilt, the cochlea to hearing, and the vertical semicircular canal is not as efficiently stimulated by this gravity-based method in the typical test position, so the horizontal canal is the focus.