Various parts of the auditory system produce electrical signals in response to sound stimulation. This objective test measures those compound electrical signals produced by the cochlea (action potential/summating potential complex) and auditory nerve. It is in effect an “ECG” of the cochlea. It can give useful information about the function of the cochlear hair cells and in particular the pressure of endolymph fluid in the surrounding membrane compartment. Because the pressure of fluid in the cochlea closely mirrors the fluid pressure in the labyrinth an EcoG may therefore give objective diagnostic information in Ménière’s disease and other allied disorders affecting inner ear fluid balance at a very early stage, before all the typical clinical features are apparent and irreversible damage has occurred.
Local anaesthetic cream will be applied to the outer surface of the eardrum. You will have surface skin electrodes placed on your head and a tiny electrode and sponge foam speaker will subsequently be inserted into the external canal of the ear that is being tested. You will hear some repetitive clicking noises but you are not required to respond to them. It is very important that you try and be as relaxed as possible, since any tension can affect the skin resistance/electrode interface and slow down the recording process. This test takes about 30 minutes to complete.