Brainstem auditory evoked response (BAER) is a test to measure the brain wave activity that occurs in response to clicks or certain tones.

Evoked auditory potentials; Brainstem auditory evoked potentials; Evoked response audiometry; Auditory brainstem response; ABR; BAEP

You lie on a reclining chair or bed and remain still. Electrodes are placed on your scalp and on each earlobe. The earphones give off a brief click or tone. The electrodes pick up the brain's responses to these sounds and record them. You do not need to be awake for this test.

You may be asked to wash your hair the night before the test.

Young children often require some type of sedation (medicine to relax them) so they remain still during the procedure.

The test is done to:

• Help diagnose nervous system problems and hearing loss (especially in newborns and children)
• Determine how well the nervous system works
• Determine hearing ability in people who can not do other hearing tests.

This test may also be performed during surgery to decrease the risk of injury to the hearing nerve and brain.

Normal results vary, and depend on the patient and the instruments used to perform the test.

Abnormal test results may be a sign of hearing loss, multiple sclerosis, acoustic neuroma, or stroke.

Abnormal results may also be due to:

• Brain injury
• Brain malformation
• Brain tumor
• Central pontine myelinolysis
• Speech disorders

There are no risks.

Brown CJ, Johnson TA. Electrophysiologic assessment of hearing. In: Cummings CW, Flint PW, Haughey BH, et al, eds. Otolaryngology: Head & Neck Surgery. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2010:chap 134.

Emerson RG, Pedley TA. Clinical neurophysiology: Electroencephalography and evoked potentials. In: Bradley WG, Daroff RB, Fenichel GM, Jankovic J, eds. Neurology in Clinical Practice. 6th ed. Philadelphia, Pa: Butterworth-Heinemann; 2012:chap 32A.