Classes of Auditory Evoked Responses

Abstract

Auditory evoked potentials arise from different neural structures, yield different types of information and suffer different limitations. In order of activation, these are

(1) Organ of Corti (0 msec latency): 'CM'; usefulness uncertain.

(2) Auditory nerve (1–4 msec): 'N₁'; practically limited to study of basal turn (high frequencies). Basis of electrocochleography; useful for certain abnormalities but not for threshold audiogram.

(3) Cochlear nucleus through inferior colliculus (3–20 msec): low voltage waves demonstrated but not clearly identified with structures.

(4) Medial geniculate and primary cortical projection area (25–50 msec): low voltage waves can yield a threshold audiogram and are stable in sleep. Inadequately exploited.

(5) Cortical projection areas; secondary response (50–280 msec): 'V potential': a slow, variable on- or off-response, but excellent for threshold audiograms in cooperative waking subjects. A DC shift during continued stimulation has also been demostrated but not exploited.

(6) Diffuse late cortical responses: a) sleep (180 msec or more): several forms including the K complex. The forms, voltage and threshold vary with the stage of sleep. Threshold audiometry is difficult and not very precise; b) awake (300 msec or more): P₃₀₀ and CNV are both related to 'expectancy' and can be combined with conditioning to test certain psychological functions.

Key Words:

• Vertex potentials
• Electric response audiometry
• Electrocochleogram
• Sonomotor response
• Recruitment