Auditory Electrophysiology

Overview of Auditory Evoked Potentials
  • AEPs are electrophysiologic responses arising from one or more sources within the peripheral and/or central auditory system structures in response to the presentation of acoustic stimuli
  • These responses, recorded from specific sites on the scalp, on the ears, or within the ears, appear as waveforms with both positive and negative voltage deflections at successive time points after the presentation of stimuli
  • In a normal functioning brain, there is spontaneous neurophysiologic activity that is present whether or not there is direct external stimulation; this is apparent on an electroencephalogram (EEG)
    • drowsy brain oscillating around 10Hz
    • sleeping brain oscillating around 3Hz
    • alert brain oscillating at or above 20Hz
  • 60Hz line noise (50Hz) of electrical outlets in the wall or from light sources in the room
  • Through signal averaging, good patient control and firm protocols, quality recordings can commence with the primary goal of reducing or eliminating background noise and capturing the desired, small amplitude AEP
Classification of Auditory Evoked Potentials
  • Latency, anatomical site of generation and by relationship to the stimulus
    • short latency potentials (<15msec)
    • middle latency potentials (15-80msec)
    • late, long or slow latency potentials (>80msec)
  • Exogenous potentials are obligatory, sensory evoked potentials largely elicited and subsequently affected by the physical parameters of the stimulus, such as stimulus intensity, rise time, frequency and duration
    • The auditory brainstem response ABR is a classic example of an exogenous potential
  • Endogenous potentials, in contrast, depend on stimulus features and more on the contextual factors related to the stimulus; these potentials have very long latencies
  • Classic examples of transient AEPs are the compound action potential (CAP) of the electrocochleogram (ECochG), the ABR, the middle latency response (MLR) arising from subcortical and cortical structures, cortical potentials (N1/P2 complexes) and the P300 cognitive potential
  • Examples of steady-state potentials include the summating potential (SP) of the EcochG, the FFR arising primarily in the brainstem and the auditory steady-state response (ASSR) arising potentially from multiple but segregated areas of the central auditory nervous system
  • The cochlear microphonic (CM) can be though of as a steady-state potential if recorded very near the cochlea, or it can be revealed in some cases of auditory neuropathy spectrum disorder, in which case the CM appears to "ring" even in response to a click stimulus
Common Name
ECochG (CM, SP, CAP)

ABR (I, III, V)

FFR

MLR (Na, Pa)

LAEP or LLR
(P1, N1, N2)

MMN

P300

N400

ASSR (<20, ~40, >60Hz)

VEMP
(P1, N1)
Latency Range (msec)
0-2


1-10

N/A

15-35

50-250


150-300

250-400

350-500

10-30


​12-27
Analysis Method
Time

Time

Time, Frequency

Time

Time


Time, Subtraction
Time

Time

Frequncy, Phase

​Time
Physiologic Description
Cochlear, Neurogenic
Neurogenic

Neurogenic


Neurogenic

Neurogenic


Neurogenic



Neurogenic

Neurogenic


​Myogenic
Anatomical Generator
Stimulus Response
Exogenous or Endogenous