An auditory brainstem response (ABR) is a test that measures electrical activity along the hearing pathway, from the inner ear through the auditory nerve and into the brainstem. It does this by playing sounds through earphones and recording the brain’s electrical reactions through small electrodes on the skin. The entire process is painless, requires no active participation from the person being tested, and takes roughly 45 minutes to complete.
How the Test Works
During an ABR test, small adhesive electrodes are placed on the scalp (typically the top of the head), behind the ear or on the mastoid bone, and sometimes on the forehead or cheek. The skin is first cleaned with a mild gel to reduce electrical interference. Once the electrodes are in place, earphones deliver a series of clicking sounds, and a computer records the tiny electrical signals your auditory system generates in response.
Those electrical signals are incredibly small, so the computer averages hundreds or thousands of responses together to create a clear waveform. This is why staying still and quiet matters. Infants are usually tested during natural sleep, and young children who can’t stay still may need mild sedation. Adults can typically lie quietly with their eyes closed.
What the Waveform Reveals
The ABR produces a characteristic pattern of five peaks, labeled waves I through V. Each wave corresponds to a specific point along the hearing pathway, and each appears within milliseconds of the sound being played. That speed is part of what makes the test so useful: it maps the auditory signal’s journey in real time.
- Wave I (around 1.5 ms): Generated by the auditory nerve fibers near the inner ear. This is the first electrical response after sound reaches the cochlea.
- Wave II (around 2.5 ms): Reflects activity at the cochlear nucleus, the first relay station in the brainstem where the signal gets processed.
- Wave III (around 3.5 ms): Corresponds to a brainstem structure involved in processing sound from both ears, which helps with locating where sounds come from.
- Wave IV (around 4.5 ms): Represents the signal traveling along the main pathway that carries auditory information upward through the brainstem.
- Wave V (around 5.5 ms): The final and most prominent peak, generated at a structure that integrates sound location and other auditory details. This is the wave clinicians rely on most heavily.
When a wave is delayed, absent, or abnormally shaped, it tells the audiologist exactly where along this pathway something may be going wrong.
Why ABR Testing Is Done
ABR serves two broad purposes: estimating hearing sensitivity and identifying problems along the auditory nerve and brainstem.
For hearing assessment, the test is especially valuable in people who can’t participate in a standard hearing test by raising their hand or pressing a button. Newborns, infants, young children, and people with developmental disabilities all fall into this category. ABR thresholds predict actual hearing levels with impressive accuracy. A large meta-analysis covering over 1,200 adults and children found that ABR thresholds predicted behavioral hearing thresholds to within 5 to 10 decibels in roughly 95% of cases. Correlations between the two measures consistently exceeded 0.87 across different sound frequencies. When hearing loss is confirmed in an infant, these ABR-based estimates are what audiologists use to program hearing aids.
For neurological purposes, ABR can help detect tumors on the hearing and balance nerve (acoustic neuromas), demyelinating diseases like multiple sclerosis that affect the brain’s nerve coatings, strokes affecting the brainstem, and a condition called auditory neuropathy where the inner ear detects sound normally but the nerve doesn’t transmit it properly.
ABR in Newborn Hearing Screening
Most newborns in the United States are screened for hearing loss before leaving the hospital, and ABR is one of the two main tools used for this. The screening version, called automated ABR (AABR), is a simplified, portable version of the full test. Three small electrodes are placed on the baby’s forehead, cheek, and neck. The device plays clicks at a set intensity (35 decibels) and automatically determines whether the baby’s response is normal, displaying a simple “pass” or “refer” result. No audiologist interpretation is needed at this stage.
The other common screening tool, otoacoustic emissions (OAE), measures sounds produced by the outer hair cells of the inner ear. The key difference is scope. OAE only checks whether the inner ear is working. ABR tests the entire pathway from the inner ear through the auditory nerve and brainstem. This is why AABR is specifically recommended for high-risk newborns: it can catch auditory neuropathy, a condition OAE screening would miss because the inner ear itself functions normally.
If a baby receives a “refer” result on screening, it doesn’t necessarily mean hearing loss is present. The next step is a full diagnostic ABR, which uses more detailed equipment, tests at multiple intensity levels, and produces the complete five-wave pattern for an audiologist to interpret. Diagnostic ABR testing at different intensity levels (from louder to softer sounds) typically takes about 80 to 90 seconds per recording at each level, though the full appointment with setup, multiple frequencies, and both ears runs considerably longer.
How ABR Differs From a Standard Hearing Test
A conventional hearing test (pure-tone audiometry) requires the person to actively respond to sounds. It’s the gold standard for anyone old enough and able to participate reliably. ABR doesn’t replace it. Instead, ABR fills the gap when behavioral testing isn’t possible or when the question isn’t just “how well do you hear?” but “where in the hearing pathway is the problem?”
ABR has a sensitivity of about 0.91 for detecting hearing loss, meaning it correctly identifies roughly 91% of people who have it. Its specificity is around 0.73, meaning about 73% of people with normal hearing get a normal result. That specificity gap is one reason a “refer” on newborn screening leads to follow-up testing rather than an immediate diagnosis. Some babies who are flagged turn out to have perfectly normal hearing.
What to Expect During the Test
For adults, the test is straightforward. You’ll recline in a comfortable chair or on a bed in a quiet room. Electrodes are attached to your scalp and near your ears with adhesive pads. You’ll hear a series of clicks or tones through earphones. There’s nothing you need to do except relax and stay still. The electrical signals being measured are generated automatically by your nervous system.
For infants and young children, preparation is the bigger concern. Babies need to be asleep for at least 45 minutes to get clean recordings, since muscle movement creates electrical noise that interferes with the test. Parents are often advised to keep the baby awake before the appointment and bring them slightly sleep-deprived so they’ll fall asleep during setup. For toddlers and young children who won’t stay still or sleep on command, light sedation administered by a medical team may be necessary. The test itself carries no risks or side effects. Nothing is inserted into the ear canal beyond a standard foam earphone tip, and the electrodes simply read electrical activity from the surface of the skin.