Electrocochleography (ECochG) is the name given to a method used in audiometry or ear, nose, and throat medicine to record electrical potentials produced by sensory cells (hair cells) in the cochlea in response to acoustic clicks or short tones at different pitches. Three different electropotentials are recorded, allowing detailed conclusions to be drawn about the function of the inner ear in the presence of a sound perception disorder.
What is electrocochleography?
Electrocochleography is used in otolaryngology. It involves measuring electropotentials generated by hair cells in the cochlea in the inner ear in response to acoustic stimuli. Electrocochleography (ECochG) is a technique that allows electropotentials generated by the hair cells in the cochlea in the inner ear in response to acoustic stimuli to be measured, recorded and compared with input signals. The main function of the hair cells in the cochlea is to convert the mechanical sound waves into electrical nerve impulses, analogous to frequency and loudness. In the ECochG, three different electropotentials are measured and recorded as electrocochleograms. These are the microphone potential corresponding to the input signals, the summation potential generated by the hair cells in response to the acoustic stimuli, and the nerve action potential delivered to the corresponding afferent fiber of the auditory nerve (vestibulocochlear nerve). In order to record the three different action potentials well, an electrode must be placed as close as possible to the cochlea. For this purpose, a non-invasive and an invasive method are available. In the non-invasive method, the electrode is placed in the external auditory canal near the eardrum. In the much better, but invasive, method, a fine needle electrode is placed through the eardrum to the cochlea.
Function, effect, and goals
In cases of identifiable hearing loss, it is important to know whether the problem is a conductive problem or a sensorineural problem in order to select a targeted therapy or technical assistance. In conductive problems, there is a dysfunction in one of the mechanical components of the auditory system in the outer ear or middle ear. Sound perception problems occur when one of the “electrical” components in the inner ear or the auditory nerve (vestibulocochlear nerve) or the processing centers in the brain are functionally impaired. A number of tests and testing procedures exist to identify a hearing problem as a conductive or a sensorineural disorder. If a sound perception problem is identified, further diagnostic procedures are used to narrow down the causative factors. The only diagnostic tool available for a detailed functional examination of the inner ear or cochlea is electrocochleography, which allows a differentiated analysis of the individual components of the cochlea. The acoustic stimuli are generated by the diagnostic device in the form of an automated sequence of so-called clicks and short tones and transmitted into the external auditory canal by means of a tiny loudspeaker or tube. The functioning sound conduction process of the hearing instrument ensures that the sound waves are transmitted to the cochlea via the eardrum and ossicles. The process of translation of sound waves into nerve action potentials by the inner and outer hair cells in the cochlea is captured and recorded by the ECochG. The insights allowed by the electrocochleogram are particularly important for development and individualization of a cochlear implant in the presence of a severe form of cochlear sensorineural hearing loss. The ECochG also serves as one of the diagnostic procedures used when Meniere’s disease is suspected. Meniere’s disease is a seizure-like disease of the inner ear, which, in addition to hearing loss and the appearance of tinnitus, is particularly associated with the sense of balance and rotational vertigo. The disease is ultimately caused by an overproduction of perilymph filling the inner ear. Often, sensorineural hearing loss or deafness is due to a dysfunction or total failure of the inner or outer hair cells, which translate sound stimuli into electrical nerve potentials in a complex process.In these cases, provided that the auditory nerve and the processing centers in the brain are intact, a cochlear implant can restore some hearing even in cases of complete deafness. This also applies to children born deaf whose cochlea is non-functional. They can be fitted with a cochlear implant at the age of less than 2 years. Their brain is still particularly capable of learning, so experience has shown that the hearing centers in the CNS can adapt particularly well to the new “hearing situation”. The implant is inserted into the cochlea and is in wireless communication with a recording device worn on the outside of the body, which uses complex algorithms to process incoming sounds and transmit them to the implant, which then stimulates the spiral ganglion. The system thus handles the entire sound processing chain from the external auditory canal, through the eardrum and ossicles in the middle ear, and including the translation of sound stimuli into nerve impulses in the cochlea.
Risks, side effects, and dangers
If electrocochleography involves an electrode placed in the external auditory canal, the procedure is noninvasive, and no chemicals or drugs are ingested, so the procedure has (almost) no risks and is also virtually free of side effects. The only risk is that the sensitive skin of the external auditory canal may react to the insertion of the electrode with inflammatory reactions, which in very rare cases may be painful and require further treatment. The risk of complications increases slightly if a needle electrode is used that is passed through the eardrum and placed in the inner ear. In principle, this gives the ECochG an invasive character. In very rare cases, as with any invasive procedure, infections and inflammation can be triggered by introduced pathogenic germs, requiring further treatment. Similarly, in extremely rare cases, inflammation can form on the perforated eardrum, leading to scarring after healing that impairs hearing.
