Caloric testing primarily assesses function of which vestibular structure?

• A. It primarily assesses the vestibulo-ocular reflex at high frequencies
• B. It measures vestibulospinal reflex integrity
• C. It assesses cochlear function
• D. It evaluates vestibular function for the horizontal semicircular canal at low frequencies

Answer: (D)

Caloric testing targets how the vestibular system responds to a very slow, low-frequency stimulus, specifically activating the horizontal (lateral) semicircular canal. By irrigating the ear with warm or cool water or air, convection currents in the endolymph of the lateral canal deflect the cupula, altering vestibular nerve firing and triggering the vestibulo-ocular reflex to produce nystagmus. Because the stimulus is extremely slow, this test best reveals the horizontal canal's function at low frequencies and is particularly useful for detecting unilateral horizontal canal weakness. It does not assess cochlear (hearing) function, nor is it a high-frequency test of the VOR (other tests like rotational chair or head impulse test cover higher frequencies).