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

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.

There is little discomfort.

The test is done to help diagnose nervous system problems and hearing losses (especially in low birth weight newborns), and to assess neurological functions.

The normal range for auditory brain stem values will vary among patients and with the instruments used.

Abnormal test results may indicate a hearing loss, multiple sclerosis, or stroke.

Additional conditions under which the test may be performed:

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

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

There are no risks.