LESSON 127

ABR waves I to V and latencies

Name: ABR waves I to V and latencies
Uploaded: 2026-11-04T04:00:00+03:00
Duration: 12 min 34 s
Description: We explain where the peaks from wave I to wave V of the auditory brainstem response (ABR) come from, and the normal absolute and interpeak latencies in adults. We also cover wave marking, the V/I amplitude ratio and the factors that affect latency, with examples.

We explain where the peaks from wave I to wave V of the auditory brainstem response (ABR) come from, and the normal absolute and interpeak latencies in adults. We also cover wave marking, the V/I amplitude ratio and the factors that affect latency, with examples.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson we will learn the waves of the auditory brainstem response, where they come from, and their normal latency values.
In the previous lesson we placed the electrodes; now we learn to read the recording on the screen.
The auditory brainstem response, or ABR, is a recording of the electrical activity in the auditory nerve and brainstem in response to sound.
This response appears within roughly the first ten milliseconds right after the stimulus.
Its amplitude is very small, usually below one microvolt, and it is buried in the background EEG activity.
So the same stimulus is given many times, often averaging one thousand to two thousand sweeps.
In averaging, the response locked to the stimulus is kept, while random noise gradually cancels out.
The peaks in the recording are numbered with Roman numerals, from I to VII.
This naming is based on the work of Jewett and Williston, who first described the response in humans in the early nineteen seventies.
In the clinic, waves I, III and V are used most, because they are the most consistently recorded peaks.
Waves II and IV are more variable; wave IV in particular often merges with wave V into a single complex.
Wave V is the largest and most robust; as intensity drops the others disappear, but it can be followed down to near threshold.
The ABR is used to estimate hearing thresholds in infants and young children who cannot do behavioral tests.
Automated ABR devices are widely used for hearing screening, especially in newborns with a history of intensive care.
Wave latencies help assess problems at the level of the auditory nerve and brainstem, that is, retrocochlear problems.
In some ear and brain surgeries, ABR recording is continued to monitor auditory nerve function.
Interpreted together with otoacoustic emissions, or OAEs, it also allows auditory neuropathy spectrum disorder to be recognized.
In this lesson our focus is the wave structure and latencies, the basis of all these uses.
The ABR waves follow, step by step, the journey of sound from the cochlea up to the brainstem.
Wave I arises from the distal end of the auditory nerve, the part close to the cochlea.
Wave II comes from the proximal part of the auditory nerve, where it enters the brainstem.
The main generator of wave III is the cochlear nucleus in the lower pons.
Wave IV arises largely from the superior olivary complex.
Wave V arises where the lateral lemniscus reaches the inferior colliculus.
These links were shown largely by direct recordings made during neurosurgery.
Waves I and II come from the auditory nerve on the side of the stimulated ear, so they are specific to that ear.
Higher in the brainstem, the pathways cross, and the later waves receive contributions from both sides.
Also, each peak after wave I arises not from a single nucleus but from the combined activity of several structures.
So the list of generators should be seen as a useful simplification for clinical interpretation.
What matters most clinically is that wave I represents the periphery, and wave V the upper brainstem.
So the time between these two waves shows how fast the signal travels through the brainstem.
This time is also called the brainstem conduction time, and we will see its normal values shortly.
To remember the order of the generators, you can use the mnemonic E COLI.
The letter E stands for the eighth cranial nerve, the auditory nerve.
C stands for the cochlear nucleus, and O for the superior olivary complex.
L stands for the lateral lemniscus and wave V, and the last letter, I, for the inferior colliculus, classically waves VI and VII.
This order also summarizes the path the signal follows up through the brainstem, from bottom to top.
Absolute latency is the time from the moment the stimulus is given to the peak of a wave.
In adults, with a high-intensity click, wave I is usually seen at about 1.5 to 1.7 milliseconds.
Wave III is at about 3.7 milliseconds.
Wave V lies between about 5.5 and 6 milliseconds.
These values are examples; each clinic should use norms obtained with its own equipment and protocol.
High intensity usually means a click at about 70 to 80 dB nHL.
Interpeak latency, or IPL, is the time between two wave peaks.
The I-III interval is about 2 milliseconds and reflects conduction from the auditory nerve to the lower pons.
The III-V interval is also about 2 milliseconds and reflects conduction in the upper brainstem.
The I-V interval is about 4 milliseconds and is the most widely used measure of brainstem conduction time.
In adults, the upper limit of the I-V interval is usually taken to be around 4.4 to 4.5 milliseconds.
The strength of interpeak latencies is that they are largely unaffected by problems in the outer and middle ear.
This is because a conductive loss delays all the waves together, so the time between them hardly changes.
Latencies are not fixed; as intensity decreases, the latency of all the waves increases.
For example, near threshold, wave V can be delayed to about 7 to 8 milliseconds.
In newborns, latencies, and especially interpeak intervals, are longer than in adults.
As the brainstem pathways mature, these values shorten and usually approach adult values by around two years of age.
Latencies are usually somewhat shorter in women than in men.
A drop in body temperature, or hypothermia, prolongs latencies; this matters for recordings in intensive care and the operating room.
As stimulus rate increases, wave V latency in particular increases, and the amplitude of the early waves decreases.
Sleep and sedation do not significantly affect the ABR; this is the main reason the method can be used in infants.
There are clear differences between newborn and adult recordings.
In a term newborn, the I-V interval is about 5 milliseconds; in adults it is about 4 milliseconds.
In newborns wave I can be relatively prominent and wave V smaller, so the V/I ratio is not judged by adult criteria.
In premature infants, latencies are even longer, and norms for corrected age are used.
So infant recordings must always be compared with age-appropriate norms.
When marking waves, we first check whether the recording is repeatable.
For this, at least two separate recordings are made under the same conditions and overlaid.
Only a peak seen in the same place in both recordings is accepted as a true response.
Waves IV and V often form a combined complex.
Wave V is marked as the peak just before the clear negative slope that follows this complex.
Wave I is the first clear positive peak; it may shrink or disappear with conductive or high-frequency loss.
For neurological click recordings, the analysis window is usually ten to fifteen milliseconds.
In infants and at low intensities, latencies are longer, so this window is widened.
The recording uses a filter passing roughly one hundred to three thousand hertz; in infants the lower limit can be set lower.
Each recording usually averages one thousand to two thousand sweeps, and the recording is repeated at least once.
The stimulus rate is set to a non-integer value such as 21.1 per second, so it does not coincide with the mains frequency.
Details such as stimulus type and polarity will be covered in our next lesson.
Amplitude is the voltage difference between the peak of a wave and the trough that follows it, measured in microvolts.
Because amplitude varies so much between people, it carries less weight than latency in interpretation.
Still, the ratio is useful: in adults, the amplitude of wave V is usually larger than that of wave I.
A clearly low V/I amplitude ratio may point to a problem at the brainstem level.
This ratio alone does not lead to a conclusion; it is assessed together with latency findings and other tests.
A clinical tip: in people with high-frequency hearing loss, wave I is often small and unclear.
In such cases, instead of an earlobe electrode, a gold-foil-covered foam ear canal electrode, a tiptrode, can be used.
Because the electrode is closer to the cochlea, the amplitude of wave I increases.
The I-V interval then becomes measurable, and the interpretation is stronger.
If all the waves are delayed but the interpeak intervals are normal, the delay usually has a peripheral source.
This picture is seen especially in conductive hearing loss.
A prolonged I-V interval suggests that the signal is travelling slowly through the brainstem and calls for retrocochlear attention.
Wave I being present while wave V is not recorded at all is also a finding that needs further assessment.
A clear difference in wave V latency between the two ears is also important; we will cover it in the neurodiagnostic ABR lesson.
The interpretations here are examples; diagnosis is always made by a physician's assessment and a test battery.
Waves I and II arise from the auditory nerve.
Wave III reflects the cochlear nucleus, and wave V the region of the lateral lemniscus and inferior colliculus.
In adults, at high intensity, wave V is seen at about 5.5 to 6 milliseconds.
The I-V interval is about 4 milliseconds and shows brainstem conduction.
Test yourself: in adults, the normal I-V interpeak latency is about how many milliseconds?
The correct answer is C: about four milliseconds.
Two milliseconds corresponds to each of the I-III and III-V intervals.
In the next lesson we will compare the click, tone burst and chirp stimuli used in ABR.
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Prerequisites

LESSON 126 Electrode placement and the 10-20