Electrocochleography

Electrocochleography (abbreviated ECochG or ECOG) is a technique of recording electrical potentials generated in the inner ear and auditory nerve in response to sound stimulation, using an electrode placed in the ear canal or tympanic membrane. The test is performed by an otologist or audiologist with specialized training, and is used for detection of elevated inner ear pressure (endolymphatic hydrops) or for the testing and monitoring of inner ear and auditory nerve function during surgery.

The most common clinical applications of electrocochleography include:

The basilar membrane and the hair cells of the cochlea function as a sharply tuned frequency analyzer. Sound is transmitted to the inner ear via vibration of the tympanic membrane, leading to movement of the middle ear bones (malleus, incus, and stapes). Movement of the stapes on the oval window generates a pressure wave in the perilymph within the cochlea, causing the basilar membrane to vibrate. Sounds of different frequencies vibrate different parts of the basilar membrane, and the point of maximal vibration amplitude depends on the sound frequency.

As the basilar membrane vibrates, the hair cells attached to this membrane are rhythmically pushed up against the tectorial membrane, bending the hair cell stereocilia. This opens mechanically gated ion channels on the hair cell, allowing influx of potassium (K⁺) and calcium(Ca²⁺) ions. The flow of ions generates an AC current through the hair cell surface, at the same frequency as the acoustic stimulus. This measurable AC voltage is called the cochlear microphonic (CM), which mimics the stimulus. The hair cells function as a transducer, converting the mechanical movement of the basilar membrane into electrical voltage, in a process requiring ATP from the stria vascularis as an energy source.

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