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User guide
ELI O S
ECH001XN111-A4 – 07/2022
20
Chapter 3
Introduction and test setup
3.1 ABR
ABR : Auditory Brainstem Response
Auditory Brainstem Response, also known as brainstem auditory evoked potentials are widely used both in the field of neu-
rological exploration and ENT. It is a non-invasive electrophysiological technique based on the principle of electroenceph-
alography (EEG), it provides objective test, reproducible information about the auditory function, from the cochlea to the
brainstem.
It shows electrical activity of peripheral auditory pathways following application of an acoustic stimulation (most often a
click) in the overall activity of the EEG.
ABR 's therefore use an averaging technique to reveal the specific auditory electro-
physiological responses (improvement of the signal-to-noise ratio).
ABR techniques are widely used for exploring the nerve conduction in the auditory pathways, latency ABR (presentation of
acoustic stimulation at a set intensity of 80dBnHL for instance) and thus revealing all the malfunctions evident in these
auditory pathways: acoustic neuroma, demyelinating diseases (multiple sclerosis, leucodystrophy...), all retro-cochlear dis-
eases and auditory neuropathy.
Furthermore, by applying acoustic stimulations of decreasing intensity, ABR's make it possible to objective hearing threshold
for each ear (threshold ABR). The ABR's inform us about the possible presence of cochlear pathologies (perception deftness
with a rise of the auditory thresholds) but also about the possible presence of diseases in the middle ear (shift of the curves).
Typical ABR plots consist of several waves numbered from I to V. In the case of latent ABR's , (neurological tracing), the
waves I, III and V must be clearly identified in a context of normality, with presence variability for waves II and IV. These
waves must appear in a normality range.
Any increase of this latency time is a sign of a conduction problem, and suggests that additional investigation is necessary.
Conventionally, and for clarity and simplicity's sake, it is accepted that wave I is generated by the distal portion of the auditory
nerve, wave II by the proximal portion, wave III by the cochlea core and wave V by the inferior colliculus contralateral to
the stimulation.
Within the scope of auditory threshold research, analysis of the ABR is centered on the evolution of wave V in the course of
decreasing intensity. The intensity at which wave V "disappears" is then associated with the intensity of the auditory threshold
for the test ear.
ABR 's is a way to objectively and non-invasive evaluating auditory function and nerve routes on newborn, child, adult
whether awake, anesthetized/sedated as in spontaneous sleep (without any alteration).