• The auditory brainstem response (ABR) is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp.

• The resulting recording is a series of vertex positive waves of which I through V are evaluated.

• These waves, labeled with roman numerals, occur in the first 10 milliseconds after onset of an auditory stimulus.

• The ABR is considered an exogenous response because it is dependent upon external factors.

• The auditory structures that generate the auditory brainstem response are believed to be as follows:[2][4]

• Wave I – generated by cranial nerve VIII• Wave II – generated by the cochlear nucleus• Wave III – generated by the superior olivary

complex• Wave IV – generated by the lateral lemniscus• Wave V – generated by the inferior colliculus

• In 1967, Sohmer and Feinmesser were the first to publish ABRs recorded with surface electrodes in humans which showed that cochlear potentials could be obtained non-invasively.

• In 1971, Jewett and Williston gave a clear description of the human ABR and correctly interpreted the later waves as arriving from the brainstem.

• In 1977, Selters and Brackman published landmark findings on prolonged inter-peak latencies in tumor cases (greater than 1 cm).

• In 1974, Hecox and Galambos showed that the ABR could be used for threshold estimation in adults and infants.

• In 1975, Starr and Achor were the first to report the effects on the ABR of CNS pathology in the brainstem.[2]

Interpretation of result

• When interpreting the ABR, we look at :• amplitude (the number of neurons firing), • latency (the speed of transmission), • interpeak latency (the time between peaks), • and interaural latency (the difference in wave V latency

between ears). • The ABR represents initiated activity beginning at the base of

the cochlea and moving toward the apex over a 4ms period of time. The peaks largely reflect activity from the most basal regions on the cochlea because the disturbance hits the basal end first and by the time it gets to the apex, a significant amount of phase cancellation occurs.