Auditory Brainstem Response (ABR): A neurological test for hearing

Posted by shalini on April 9th, 2019

Auditory brainstem response audiometry is a neurologic test, that is designed for auditory brainstem function in response to auditory stimuli. This test is the most common application of auditory evoked responses. This test tells us how well the inner ear (cochlea), and the brain pathways for hearing are functioning. This test is also called an Auditory Evoked Potential (AEP). This test is mainly used who cannot complete a typical hearing screening. If your symptoms are of the hearing loss in the brain or in a brain pathway ABR test is recommended. The test is performed and interpreted by an audiologist.

*ABR stands for Auditory Brainstem Response.

What is the Purpose of an ABR?

The ABR has two main clinical functions: to find threshold and neurological assessment. A threshold is find using click and tone-burst stimuli with air and bone conduction are typically what we are using for infants to estimate hearing sensitivity, For adults, we simply use ABR for a neurological assessment to evaluate the integrity of the auditory system. With this, we compare waveform latencies for a further rate study.

Brainstem evoked response audiometry is a useful assessment technique of hearing. This test is considered to be an exogenous response because it depends on external factors.

How the ABR test is performed?

Put electrodes on your head to get ready for the ABR. ABR audiometry refers to an evoked potential generated by a brief tone pip transmitted from an acoustic transducer in the form of an insert earphone or headphone. The elicited wave response is measured by surface electrodes typically placed at the vertex of the scalp and ear lobes. The electrodes are stuck to your skin and connected to a computer. They record brain wave activity in response to sounds you hear through earphones. All you have to do is rest quietly during the test. During the test, you do not have to say or do anything. The person doing the test will see the results on a computer.

What is Click-ABR?

The click sound alerts the whole cochlear, it has been found that the ABR thresholds obtained by clicks match the behavioral thresholds only at high frequencies. The ABR represents the synchronous electrical activity of many neurons arising from areas within the cochlea, and brainstem in response to an auditory stimulus. How do we determine if a response is present and how do we determine the threshold? First, a response must be repeatable with good morphology. That is very important. It must follow the typical pattern when intensity is changed. If intensity is decreased, latency should get longer and amplitude should get smaller. Absolute latency should be appropriate for the patient's age. This is determined by comparing marked responses to age and gender appropriate normative data.

Result and Conclusion of the test

The result of this test is recorded as a series of six to seven vertex positive waves, where from I to V are evaluated by experts. These waves recorded just after the onset of an auditory stimulus. These waves are labeled with Roman numerals in Jewett and Williston convention. A major advantage of this test is its ability to test even infants in whom conventional audiometry may not be possible. The investigation can be used as a screening test for deafness or people with hearing loss in high-risk infants. Early diagnosis and rehabilitation will reduce disability.