Evoked Potential Audiometry Assessment
Hearing involves not only the ear, but also the brain. When a sound is heard, we expect some change in the electrical activity of the brain. These minute voltage variations in response to sounds are called AUDITORY EVOKED POTENTIALS. Auditory evoked potentials which occur in the first ten milliseconds after the presentation of a sound originate in the part of the brain called the brainstem and are called the AUDITORY BRAINSTEM RESPONSE(ABR).
The ABR is recorded from scalp electrodes placed on the head, forehead, and earlobes. Each ear is tested separately with an earphone. The patient does not respond to the sounds and can even sleep during the test. Sounds called "clicks" are presented at various loudness levels and at different speeds. The response, which is detected by the electrodes, is amplified, averaged, and stored in the computer. The click produces synchronized responses from the inner ear and the brainstem. The response resembles a series of five wave forms, which are labeled with Roman numerals.
The ABR is a non-invasive, objective test, which can be used as an estimate of hearing loss or for assessment of neurological function. The degree and type of hearing loss can be determined from the presence or absence of waves, the time (latency) at which certain waves occur, and the time interval between different waves. ABR can also assess the functional integrity of the central auditory pathway, and can detect abnormalities, such as acoustic tumors.