Origins of ABR

Abstract

The ABR (Auditory Brainstem Response) is the neurological activity that is generated and transmitted along the auditory neural pathways from the cochlea on its way to the medial geniculate body (MGB) in the brain.

This response, which can be recorded from external electrodes pasted onto the skull and mastoid process of the subject, is therefore called a “far-field recording” which means that the electrodes recording this response are externally placed on the skull, quite distant from the actual neurologic activity within the brainstem.

Stereotypical in that this ABR waveform is remarkably similar in overall form across mammalian species (human, simians, cats, rabbits, etc.). As this response traverses the neurological substrate, it passes through various nuclei which each generate a positive potential (wave), the ABR waveform, related to its source (P1; cochlear nerve, P2; cochlear nucleus, P3; superior olivary complex, P4 and P5; lateral lemniscus nucleus and inferior colliculus, P6; brachium of inferior colliculus, and MGB in the brain). Neurophysiological knowledge of the sources, peak latencies and amplitudes of these seven waves are clinically valuable not only for evaluating peripheral hearing loss but also in localizing lesions within the eighth cranial nerve over its length from the cochlea to the midbrain inferior colliculus.