Primer on 12 principles of vestibular physiology

Vestibular physiology can be confusing, especially when  discussion focuses on hard to recall facts and jargon (e.g.., "Is the horizontal canal excited by ampullopetal or ampullogfugal endolymphatic flow?") or mnemonics that highlight the direction of nystagmus quick phases (e.g., "cold opposite, warm same" for caloric testing, "geotropic" for posterior canal BPPV) rather than the nystagmus slow-phase eye movements driven by the vestibulo-ocular reflex.   To help make the material more accessible, co-authors John P.  Carey MD and Charles C. Della Santina PhD MD typically present core vestibular physiology concepts organized into 12 principles that are easy to remember and can be used to intuitively work out  relationships between head motion, other stimuli, labyrinth activity and reflexively driven eye, head and body movements.  

For a full description, see the Carey & Della Santina chapter Principles of Applied Vestibular Physiology in Cummings Otolaryngology, which is freely accessible electronically for many readers via university and hospital libraries and available directly from the publisher (Elsevier) or book sellers such as Amazon.  The publication date for the 8th edition of Cummings Otolaryngology is 2025-11-06.  Students in the Johns Hopkins School of Medicine Structure and Function of the Auditory and Vestibular Periphery (BME 580.625/6) course can access a copy of Dr. Della Santina's lecture slides (which draw heavily from a slide set initially created for the course by Dr. Carey) below.

• Principle 1: The vestibular system primarily drives reflexes to maintain stable vision and posture.

• Principle 2: By modulating the non-zero baseline firing of vestibular afferent nerve fibers, semicircular canals encode rotation of the head, and otolith organs encode linear acceleration and tilt.

• Principle 3: Stimulation of a semicircular canal produces eye movements about the axis of that canal.

• Principle 4: A semicircular canal is normally excited by rotation in the plane of the canal bringing the forehead toward the ipsilateral side.

• Principle 5: Any stimulus that excites a semicircular canal’s afferents will be interpreted as excitatory head rotation in the plane of that canal.

• Principle 6: For high accelerations, head rotation in the excitatory direction of a canal elicits a greater response than does the same rotation in the inhibitory direction.

• Principle 7: The response to simultaneous canal stimuli is approximately the sum of the responses to each stimulus alone.

• Principle 8: Nystagmus due to dysfunction of semicircular canals has a fixed axis and direction with respect to the head.

• Principle 9: Brainstem circuitry boosts low frequency vestibulo-ocular reflex performance through “velocity storage” and “neural integration.” Failure of those mechanisms suggests central pathology.

• Principle 10: The utricle senses both head tilt and translation, but loss of unilateral utricular function is interpreted by the brain as a head tilt toward the opposite side.

• Principle 11: Sudden changes in saccular activity evoke changes in postural tone.

• Principle 12: The normal vestibular system can rapidly adjust the vestibular reflexes according to the context, but adaptation to unilateral loss of vestibular function may be slow and susceptible to decompensation.