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Physiology of the ABR
Auditory Brainstem Response
Megan D. Ford, M.A., CCC-A
Sullivan, 2000
Auditory Brainstem Response(ABR)
• Waveforms of ABR first labeled with Roman numerals by Jewett and Williston (1971).
• The summed responses of the synchronous firing of large numbers of VIIIth nerve and auditory brainstem neurons.
Auditory Brainstem Response(ABR)
By measuring the amplitude and latencies of each of the five major waves of the
ABR, one can objectively estimate hearing levels, screen for retrocochlear pathology
and monitor the VIIIth nerve intraoperatively.
Auditory Brainstem Response
• Click or toneburst stimuli generate a response that travels the auditory pathway
• The response is measured using surface electrodes and plotted as five peaks and troughs
• The positive peaks are generated from multiple axonal pathways in the auditory brainstem
Components of the ABR:Waves I and II
True action potentials Wave I (AKA: AP – action potential of the
EcochG) generated from distal portion of the VIIIth nerve Specifically, VIIIth nerve firing due to activity in the
basal portion of the cochlea Wave II generated from the proximal VIIIth
nerve, as it enters the brainstem
Components of the ABR: Wave III
Second-order neuron activity Peak comes from in or near the cochlear
nucleus Trough arises from the trapezoid body Generated in the caudal portion of the
auditory pons
Components of the ABR: Wave IV
Often seen tagging along on Wave V Arises from pontine third-order neurons,
mostly located in the superior olivary complex
Contributions from cochlear nucleus and nucleus of the lateral lemniscus
Components of the ABR: Wave V
Positive peak related to the termination of the lateral lemniscus as they enter inferior colliculus
Negative trough attributed to dendritic potentials within the inferior colliculus
Let’s not forget the Cochlear Microphonic
An alternating current potential that mocks the stimulus Not to be confused with stimulus artifact
Arises from the outer hair cells
Cochlear Microphonic
Berlin, et al, 2002
Can be seen by alternating the polarity of the stimulus (Rarefaction versus Condensation)
Interpreting the Results
Yoshinaga, et al, 2003
Evaluating the ABR response
Analyze the absolute latency of wave V and compare to:
Normative dataThe other ear (Interaural difference)
Results that fall out of the normal range suggest retrocochlear pathology
Evaluating the ABR response
Analyze interpeak intervals (I-III, III-V, I-V) and compare to:
Normative dataThe other ear’s interpeak intervals
Results that fall out of the normal range suggest retrocochlear pathology
Evaluating the ABR response
Absent response in the involved ear:
Absent wave I usually correlates with cochlear pathology
Absent wave III-V or absent ABR is suggestive of retrocochlear pathology
Evaluating the CM response
When CM is present in the absence of ABR waveforms, may indicate “auditory neuropathy”
Often, a present CM correlates with robust oto-acoustic emissions
Considerations in Interpretation:
Many factors affect the ABR response:
• Degree and type of hearing loss• Intensity of signal• Rate of the signal• Type of signal (click versus toneburst)• Recording montage• Pathology
Bibliography
• Hall JW III: Handbook of Auditory Evoked Responses. Needham Heights, MA: Allyn & Bacon; 1992
• Jacobson J: Principles & Applications in Auditory Evoked Potentials. Needham Heights, MA: Allyn & Bacon; 1994
• Scott M: Auditory Brainstem Response Audiometry. eMedicine. http://www.emedicine.com/ent/topic473.htm; 2005
• Webster D: Neuroscience of Communication. San Diego, CA: Singular Publishing; 1995
