Electrocochleography: the electrical response of the cochlea

What does electrocochleography record?

When sound reaches the inner ear, the cochlea generates electrical activity even before the signal travels along the auditory nerve. Electrocochleography captures that activity in the first milliseconds and separates two components:

• The summating potential, which reflects the behaviour of cochlear structures during the stimulus.
• The action potential, corresponding to the firing of auditory nerve fibres.

What matters clinically is above all the relationship between the two. Where there is excessive fluid build-up in the inner ear — endolymphatic hydrops — that relationship tends to change in a characteristic way.

When is it indicated?

• Suspected endolymphatic hydrops, in people with attacks of vertigo accompanied by hearing loss that comes and goes, tinnitus and a sense of fullness in the ear.
• Follow-up of patients already in treatment, where the physician wishes to compare tests over time.
• Investigation of specific hearing losses, where what arises from the cochlea must be separated from what arises from the nerve.

How is it carried out?

1. The skin of the forehead is cleaned and adhesive electrodes are applied.
2. A soft electrode is positioned at the entrance to the ear canal.
3. Headphones deliver sequences of sound stimuli.
4. You lie still, at rest and in silence, while the equipment records the responses.

Movement and muscle tension create interference, which is why the test calls for stillness.

How is the result read?

The report presents the recorded potentials and the relationship between them, compared with reference values. Two caveats matter and apply to every case:

1. An abnormal result supports the hypothesis; it does not confirm it. The diagnosis of Ménière’s disease is clinical, built from the pattern of attacks, the audiogram and the history.
2. A normal test does not rule the disease out. Hydrops may not be present at the moment of testing, particularly between attacks.

Electrocochleography therefore enters as one piece of the investigation, alongside audiometry, the balance tests and the consultation. The wider context is described on the page on dizziness and vertigo.

Where it is carried out

At Clínica Rhinus, in the Renascença district of São Luís. The test is performed by the speech-language pathologists on our team and the result is discussed at the consultation with the ENT specialist.

How should I prepare for this test?

• Bring the medical request: it is required for all tests, whether under insurance or self-pay.
• Wash the hair beforehand and do not use gel, cream or oil, which interfere with electrode contact.
• Do not use make-up, sunscreen or moisturiser on the face on the day of the test: they interfere with electrode contact.
• If there is a lot of wax in the ear canal, it may need to be removed beforehand.
• Avoid exposure to loud noise in the hours before the test.
• Come rested: the test requires lying still and relaxed for several minutes.
• Bring your audiogram and any previous balance tests.

Sources: Brazilian Society of Otology · Flint PW, Francis HW, Haughey BH, et al. Cummings Otolaryngology: Head and Neck Surgery. 7th ed. Elsevier; 2020. · Bento RF, Bittencourt AG, Voegels RL. Seminários em Otorrinolaringologia. Fundação Otorrinolaringologia.