The BAEP consists of a series of up to seven components (identified by Roman numerals) that occur within 10 msec of the click stimulus and are generated in different regions of the peripheral and central auditory pathways. Wave I and the early part of wave II represent the auditory nerve action potential. Wave III probably arises in the region of the superior olive, whereas waves IV and V arise in the midbrain and inferior colliculus. Waves VI and VII are of uncertain origin and, because of their inconsistency in normal subjects, are of little clinical utility.
The most consistent components are waves I, III, and V, and it is to these that attention is directed when BAEPs are evaluated for clinical purposes. The absolute latency of these components, the intervals between them (the so-called interpeak latencies), and the amplitude of wave V relative to wave I are assessed. Interside differences in interpeak latency are also measured and may reveal minor abnormalities. F.!9„U.(e.2.4:.1.3 illustrates a normal response.
Figure 24-13 Brain stem auditory potential elicited by monaural stimulation at 75 dBSL and recorded with an ipsilateral mastoid referenA, a normal subject, andB, a patient with a structural lesion involving the upper pons. Two trials are superimposed to show the replicability of the findings. It can be seen that waves IV and V are markedly attenuated in the response records.! in
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