1Introduction & history
Electrocochleography is the oldest of the clinical auditory evoked potentials — older than ABR, older than OAEs — and the one with the most distinctive view of the cochlea. This module sets out what the test measures, how it earned and then lost and then partially regained its place in clinical audiology, and the reader-level scheme the rest of the atlas uses to keep foundation, trainee, and clinician material distinct.
FWhat ECochG measures
Electrocochleography (ECochG) records the electrical activity generated by the cochlea and the most peripheral segment of the auditory nerve in response to sound. Three components ride on every well-recorded trace:
- The cochlear microphonic (CM), an alternating potential that follows the stimulus waveform, generated mostly by outer hair cell receptor currents.[2008]
- The summating potential (SP), a DC shift riding through the stimulus interval, generated by a mixture of hair-cell and dendritic currents.[1954, 2019]
- The compound action potential (AP / CAP / N1), a large negative peak around 1.5–2.0 ms after a click at 90 dB nHL, generated by the synchronous firing of distal auditory nerve fibres at the cochlear base.[1981, 2014]
Of those three, the AP is the same physiological event as ABR wave I — recorded much closer to its generator. The CM and SP are onlyavailable to ECochG; ABR's band-pass filtering removes both. This is the fundamental reason ECochG and ABR are complementary tests rather than substitutes — Module 13 develops that point in detail.
ECochG samples the cochlea and the most peripheral auditory nerve. It does not sample brainstem auditory processing (waves II–V of the ABR), it does not measure pure-tone thresholds directly, and it does not reliably detect tumours that sit proximal to the wave-I generator at the cochlear base — most vestibular schwannomas, in other words. Module 10 covers that limitation; Module 13 covers how to combine ECochG and ABR to capture the full peripheral and brainstem picture.
FA short history
ECochG is older than every other clinical auditory evoked potential in routine use. A condensed timeline:[2017]
| Year | Milestone | Why it matters |
|---|---|---|
| 1930 | Wever & Bray report a microphone-like response from the cat auditory nerve | First demonstration that the cochlea generates an electrical signal in response to sound (the "Wever–Bray effect", later resolved into CM + neural activity). |
| 1935 | Fromm, Nylén & Zotterman record the CM from the human promontory | First human cochlear recording — three decades before clinical ABR existed.[1935] |
| 1954 | Tasaki, Davis & Eldredge describe the summating potential in guinea pig | Identifies the third component sitting between CM and AP — the future Ménière's biomarker.[1954] |
| 1965 | Davis proposes the "battery model" of cochlear transduction | Endocochlear potential as bias supply for hair-cell MET — the framework still used to explain SP and CM generation.[1965] |
| 1971 | Eggermont introduces transtympanic ECochG into routine clinical use | Establishes the protocol that dominated the next two decades. |
| 1981 | Picton, Stapells & Campbell publish normative latency-intensity data | The canonical reference for AP latency vs intensity, still cited as the basis for distinguishing conductive, cochlear, and retrocochlear LIF patterns (see Module 4).[1981] |
| 1980s–90s | ABR and MRI become dominant for retrocochlear workup; ECochG retreats | The non-invasive ABR (and especially gadolinium MRI) supersede ECochG's historical role in schwannoma screening. The field nearly disappears from routine audiology. |
| 1999 | Ferraro & Tibbils formalise the SP/AP area ratio for Ménière's | Anchors the modern hydrops protocol; Module 5 covers its sensitivity and limits in detail.[1999] |
| 2009 | Kujawa & Liberman demonstrate "hidden" cochlear synaptopathy in mice | Opens a possible new clinical role for ECochG (Module 11), though the human translation is still contested.[2009] |
| 2015 | Campbell, Briggs & O'Leary record ECochG via the cochlear implant's own electrodes | The enabling technology for intraoperative monitoring during CI surgery — the growth area of modern clinical ECochG.[2015] |
| 2022 | Campbell et al. publish a single-blinded RCT of intraoperative ECochG-triggered intervention | The first level-1b evidence that intraoperative ECochG improves residual-hearing preservation. Module 12 builds around this trial.[2022] |
| 2025 | Andonie et al. extend single-amplitude thresholds into multimodal feature analysis | Direction-of-travel for the field — ML-derived alarm thresholds, multifrequency stimulation, integration with impedance and electrode-position telemetry.[2025] |
The shape of that timeline is worth pausing on. ECochG had a clinical golden age in the 1970s and 80s as the principal electrophysiological window onto retrocochlear pathology, lost that role almost entirely to non-invasive ABR and MRI by the late 1990s, and re-entered routine practice in the 2010s through a completely different door — endolymphatic hydrops monitoring, third-window characterisation, and (most consequentially) intraoperative monitoring during cochlear implantation. The modules in this atlas are organised around the conditions where the test now earns its keep, not the conditions it used to be used for.
FWho this atlas is for
This atlas is written for three overlapping audiences:
- Medical students and foundation-year trainees encountering ECochG for the first time and wanting to understand what it measures and where it fits in the wider auditory workup.
- Audiology trainees and ENT registrars building practical interpretation skills — reading traces, understanding the diagnostic measurements (SP/AP ratio, area ratio, latency-intensity function), and learning when ECochG is the right test and when it is not.
- Clinicians who already perform or interpret ECochG and want a curated, evidence-anchored synthesis of the contemporary literature — with emphasis on the sensitivity and specificity limits that mean the test is supportive in most settings rather than diagnostic on its own.
FHow to read the atlas — the F / T / C level scheme
Each section heading throughout the atlas carries one or more coloured level markers indicating the intended audience:
| Marker | Audience | What to expect |
|---|---|---|
| F Foundation | Medical students, early trainees, generalists who want the concept and the clinical headline | Plain prose, minimal jargon, headline diagnostic rules, no electrophysiological deep-dives. |
| T Trainee | Audiology / ENT / neurotology trainees actively building interpretation skills | Diagnostic measurements with cutoffs, common pitfalls, the practical "how to read" level. Most module pages spend most of their length here. |
| C Clinician | Qualified clinicians who already perform or interpret ECochG | Sensitivity/specificity numbers, mechanistic nuance, edge cases, recent evidence (RCT-level where it exists), and the honest limits of the test. |
A section can carry more than one marker — for example a well-written interpretive section may matter equally for foundation and trainee readers, in which case it carries both. Use the markers as a reading guide: F sections are safe to read first; T sections build on the F material; C sections assume the T material and add the evidence and edge cases that come with clinical responsibility.
FModule roadmap
The fourteen modules of the atlas fall into four broad groups:
| Group | Modules | What they cover |
|---|---|---|
| Foundation | 2 Anatomy, 3 Technique, 4 Normal waves | The biology, the recording technique, and what a normal trace looks like. Read these first. |
| Hydrops and third-window | 5 Ménière's, 6 SCD | The two conditions where the SP/AP ratio is the headline finding, and how to tell them apart when the trace alone cannot. |
| Neural and synaptic | 7 ANSD, 11 Synaptopathy | The pathognomonic CM-present-AP-absent pattern of ANSD, and the contested human translation of the cochlear-synaptopathy hypothesis. |
| Other clinical questions | 8 Sudden SNHL, 9 Perilymph fistula, 10 Schwannoma, 12 Intraoperative CI, 13 ABR overlap | Conditions and situations where ECochG plays a smaller or different role — sometimes adjunctive, sometimes superseded, sometimes (as with intraoperative CI monitoring) the most consequential current application of the test. |
| Tools and references | 14 Tools | The SP/AP ratio calculator, the glossary, the full references list, and the changelog. |
It is not a substitute for hands-on training in ECochG recording or for the clinical judgment that comes from interpreting traces in real patients. The diagnostic measurements and cutoffs throughout the atlas are explicitly interpretive anchors, not standalone diagnostic criteria. Every disease module is written from the position that ECochG is supportive — sometimes strongly so — but almost never standalone diagnostic. Where it is closest to standalone diagnostic (the polarity-reversal pattern of ANSD in Module 7), the atlas is explicit about why.
Ready to start? Module 2 — Anatomy & physiology sets out the cochlear biology underneath every later module.