An auditory brainstem response test is used to measure the pathways in the brain responsible for hearing. Electrodes are placed around the patient’s forehead and ears and headphones are placed in their ears. In order to get a good reading, the patient is asked to lie down in the sound booth and stay still for the duration of the two-hour test. The patient’s brain wave reaction to the clicks emitted from the headphones is measured.
While a non-invasive test, sedation is typically needed if this test must be performed on a child that cannot stay still.
There are a few variations of this test used to specifically evaluate the patient’s equilibrium: Electrocochleography (ECoG) and Vestibular Evoked Myogenic Potentials (VEMP). ECoG is used to measure the cochlea’s response to stimuli. This helps to determine if the cochlea is working correctly or if there is a buildup of fluid. A buildup of fluid inside the cochlea can lead to hearing loss, dizziness and tinnitus. The placement of the electrodes differs between the ECoG and the ABR, as they must be placed as close as possible to the cochlea in order to pick up information.
Vestibular evoked myogenic potential (VEMP) evaluates the function of the saccule, an important part of the middle ear that helps maintain balance by translating head movements into neural impulses which are sent to the brain. These neural impulses also cause the sternocleidomastoid (SCM) neck muscles to relax. The VEMP test requires electrodes to be placed on the SCM neck muscle while the patient is lying down in the sound booth. The patient will then be instructed to raise their head; this movement flexes the SCM neck muscles. The saccule is then stimulated by loud tones, the relaxation of the patient’s neck muscles are measured.