By: Catherine Joachin
Introduction
The vestibulocochlear nerve, also known as cranial nerve VIII, is the bundle of axons that relays signals related to hearing and balance to the brain (Cleveland Clinic, 2024). This structure is made up of two components, the vestibular nerve and cochlear nerve, each with distinct separate functions.
- The vestibular nerve is responsible for carrying information pertaining to head movement and position from the vestibular organs (I.e., utricle, saccule and semicircular canals located inside the inner ear) to the brain, which uses then it to maintain spatial orientation and balance/equilibrium.
- The cochlear nerve transmits auditory information from the cochlear (the spiral-shaped cavity within the ear) to the brain, enabling hearing.
(Cleveland Clinic, 2024)
Neuroanatomy
The vestibulocochlear nerve passes through a bony canal known as the internal auditory canal (IAC), which connects the inner ear to the base of the skull (Cleveland Clinic, 2024). Before entering this canal, projections from the spiral and vestibular (Scarpa’s) ganglions create the cochlear and vestibular nerves, respectively. It is within the IAC that these two sets of fibres combine to form cranial nerve VIII (Bordoni, Mankowski & Daly, 2023). CN VIII travels through the cerebellopontine angle (CPA) (i.e., triangular region at the junction of the cerebellum and the pons) and enters the brainstem (Bordoni, Mankowski & Daly, 2023). There, the nerve separates into vestibular and cochlear components once more to reach corresponding nuclei located in the brainstem (Bordoni, Mankowski & Daly, 2023; Cleveland Clinic, 2024).
Damage to the vestibulocochlear nerve typically involves injuries or pathological processes linked to the cerebellopontine angle, the internal auditory canal or the inner ear (Bordoni, Mankowski & Daly, 2023 ). This can lead to symptoms of hearing loss, dizziness, nausea, tinnitus (hear ringing), nystagmus (rapid, uncontrollable eye movements) and vertigo (Cleveland Clinic, n.d.).
Cranial Nerve VIII and Epilepsy
Cranial nerve stimulation (CNS), a neuromodulatory approach targeting specific brain pathways, has emerged as a promising therapeutic intervention for neurological disorders, including epilepsy (Adair et al., 2020). While stimulation of cranial nerve IX (also known as vagus nerve stimulation or VNS) has become a recognized treatment option for seizure control in drug-resistant epilepsy, researchers have looked into arousing other cranial nerves for therapeutical benefits. Thus far, research into glossopharyngeal nerve (cranial nerve IX) stimulation highlights a potential therapeutic role in seizure control for its afferent branch, the nerve of Hering (HN), which shares the vagus nerve’s brainstem nucleus (Adair et al., 2020).
To date, no studies have linked the electrical stimulation of the eighth cranial nerve to either epilepsy or seizure control; however, vestibulocochlear nerve stimulation can lead to vestibular symptoms that resemble those experienced by individuals with temporal and parietal lobe epilepsy, including dizziness, involuntary eye movements or vertigo, although the origin of these symptoms differ (Hewett & Bartolomei, 2013).
Conclusion
The vestibulocochlear nerve is a collection of important sensory neurons that communicate information pertinent to body equilibrium, eye movements and hearing. While there is no direct association between the vestibulocochlear nerve and epilepsy, vestibular symptoms share similarities with symptoms experienced in temporal and parietal seizures.
References
Bordoni B., Mankowski N.L. , Daly D.T. (2023, May 22) Neuroanatomy, Cranial Nerve 8 (Vestibulocochlear). In StatPearls. StatPearls Publishing. Retrieved from: https://www.ncbi.nlm.nih.gov/books/NBK537359/
Cleveland Clinic. (2024, October 14). Vestibulocochlear nerve. Cleveland Clinic. https://my.clevelandclinic.org/health/body/vestibulocochlear-nerve
Devin Adair, Dennis Truong, Zeinab Esmaeilpour, Nigel Gebodh, Helen Borges, Libby Ho, J. Douglas Bremner, Bashar W. Badran, Vitaly Napadow, Vincent P. Clark, & Marom Bikson. (2020). Electrical stimulation of cranial nerves in cognition and disease Electrical stimulation of cranial nerves in cognition and disease. Brain Stimulation, 13(3), 717–750.
Hewett, R., & Bartolomei, F. (2013). Epilepsy and the cortical vestibular system: tales of dizziness and recent concepts. Frontiers in Integrative Neuroscience, 7, 73–73. https://doi.org/10.3389/fnint.2013.00073
