Brainstem Auditory Evoked Response (BAER) Testing
Brainstem Auditory Evoked Response (BAER) evaluation is a non-invasive hearing test that allows the Board-Certified Veterinary Neurologists at Southeast Veterinary Neurology to confirm the existence of hearing loss. This specialized test for dogs and cats takes approximately 10-15 minutes and tests each ear individually.
Any interruption in the delivery of sound to the brain results in one of several types of deafness:
- Conductive deafness – due to interference in the transmission of sound waves to the inner ear, for example, caused by a foreign body or wax in the ear canal, rupture of the ear drum or infection in the middle ear.
- Sensorineural deafness – results from damage or defect in any part of the auditory (hearing) pathway from the cochlea in the inner ear, via the auditory nerve to the auditory cortex of the brain.
- Congenital deafness – present at birth, while late onset deafness, as its name suggests, occurs later in life, such as hearing loss associated with old age.
- Inherited deafness – passed down through one or both parents, whereas acquired deafness is due to external factors such as injury or disease.
During brainstem auditory evoked response (BAER) testing, earphones deliver a series of clicks to each ear. The BAER test records the electrical activity in the auditory nerve pathway from the inner ear receptors through the brainstem to the cerebral cortex. Brainstem auditory evoked responses are evoked potentials used to detect, localize and monitor auditory and neurological deficits. No response is seen in auditory nerve disorders associated with hearing loss. Brainstem disorders may also alter the BAER.
Congenital deafness (deafness at birth) is recognized as a problem in many breeds of dog that carry the extreme piebald gene, demonstrated by a predominantly white coat. Such breeds include Dalmatians, English Setters, white Boxers and white English Bull Terriers. Deafness in these breeds can occur due to degeneration of structures in the cochlea. BAER testing can provide an instantaneous yes-or-no result through the assessment of the waveforms generated by the test.
If you have a litter from a breed that is at risk of congenital deafness, the best age to test is around 5 ½ to 6 ½ weeks of age. It is not possible to assess hearing in puppies before the ear canals open at 12-14 days as sound waves cannot enter. The test can be carried out at any age after this, including on adult dogs; however, many breeders wish to know the hearing status of their pups before they go to their new homes.
Different types of animals can have their hearing tested using the BAER, including cats. White cats, especially those with one or more blue eyes, are also prone to congenital deafness and may be tested in the same way as dogs. Many cats will not tolerate the hearing tests without sedation but some will be fine without. Kittens may be tested from eight weeks of age onwards and it is always attempted without sedation first.