ECochG is a variant of brainstem audio evoked response (ABR) where the recording electrode is placed as close as practical to the cochlea. We will use the abbreviation ECOG and ECochG interchangeably below. ECOG is preferable to us as it is shorter. ECOG is intended to diagnose Meniere's disease, and particular, hydrops (swelling of the inner ear). ECOG may also be abnormal in perilymph fistula, and in superior canal dehiscence. The common feature connecting these illnesses is an imbalance in pressure between the endolymphatic and perilymphatic compartment of the inner ear. ECOG can also be used to show that the cochlea is normal, in persons who are deaf. The cochlear microphonic of ECOG may be normal in auditory neuropathy (Santarelli and Arslan 2002) as well as other disorders in which the cochlea is preserved but the auditory nerve is damaged (Yokoyama, Nishida et al. 1999). Finally, ECOG's have also been used to as a indicator of the temporary threshold shift that may follow noise injury (Nam et al, 2004).

1. SEMINAR ON
RECENT ADVANCEMENTS IN
ELECTROCOCHLEOGRAPHY (ECOCHG)
Mukesh Sharma
Ph.D. Scholar (ASLP)
Session (2022-23)

2. Electrocochleography (ECochG) involves the measurement of
stimulus-evoked potentials generated by cochlear hair cells and
auditory nerve fibers (Eggermont, 2017).
HISTORY: (Surgical & Non-surgical recording period)
The CM was first discovered in 1930 by Ernest Wever and Charles
Bray in cats.
Fromm et al. (1935),were the first to employ the ECochG technique
in human by inserting electrode through the TM and recorded the
CM from the round window & cochlear promontory.
Introduction:

3. Lempert et al. (1947) coined the term “Cochleogram”.
The SM, a stimulus-related hair cell potential, was first described
by Davis et al. (1950) & later Tasaki et al. (1954).
Ruben (1961), was the first to record CAP. Non-surgical period
started in 1967.
Moore (1971), recorded CM & AP using surface electrode.
ECochG was used in the diagnosis of Meniere’s disease in late
1984.
In 1990s, things picked up again in the following 12 years with
improving the use of ECochG in the diagnosis of Meniere’s
disease.
Number of articles, usefulness of ECochG was improved by 2010.

4. PRINCIPLES OF ECOCHG
 Both Inner Hair Cells (IHC) and Outer Hair Cells (OHC)
generate receptor potentials in response to sound (Russell &
Sellick, 1978; Dallos et al., 1982).
 Compound responses from the cochlea reflecting these hair
cell potentials can be recorded at round window, TM or even
from the scalp and can be used clinically.
 These responses are called as Cochlear Microphonics (CM)
and Summating Potential (SP).

5. ELECTROPHYSIOLOGY
 ECochG measures electrophysiological responses from
the cochlea and the auditory nerve (Bakhos et al.,
2017).
 During ECochG, a brief duration of acoustic stimuli
(clicks or acoustic tone bursts) of alternating polarity is
used to elicit electrophysiological responses that can be
measured using skin electrodes, extra tympanic
electrodes, transtympanic electrodes, or intracochlear CI
electrodes (Gibson WP, 2017).
 An acoustic tone burst generates electrophysiological
responses from a localized region in the cochlea or the
auditory nerve, whereas clicks are known to elicit
responses across a broader frequency range.

6. ECOCHG COMPONENTS:
CM- AC- OHC.
ANN- phase-locked
signal - AN
SP and CAP are
direct currents.
SP – OHC & IHC
CAP - AN

7. Cochlear Microphonic:- (CM)
o The CM is produced almost exclusively from OHC receptor currents
and when recorded from the round window, dominated by the
responses of OHCs in the basal turn (Russell, 2008).
 Alternating current (AC) voltage that reflects the instantaneous
displacement of the basilar membrane along some distance defined
by the effective site of the recording within the cochlea, the method
of recording and the stimulus conditions.
The popularity of CM in the laboratory derives from,
 Its link to cochlear transduction.
 Its sensitivity to the health of the cochlear partition.
 The relative ease with which it can be recorded within the fluid
spaces of the cochlea.

8.  CM mimics the stimulus, so it is difficult to separate it
from stimulus artifact.
 CM is sensitive to changes in middle ear transmission
characteristics.
 CM follows polarity of click stimulus, summing or
averaging the response to stimuli of alternating polarity
will generally cancel out the CM (Yoshie, 1981).
 Reductions in CM magnitude have been reported for
various disorders such as MD & vestibular
schwannomas (Gibson & Beagleus 1976)

9. Summating Potential (SP):
 It is a complex response made up of
several components.
 It is direct current shift receptor potential reflecting
cochlear electrical activity in response to acoustic
stimulation.
 It follows envelops of the stimulus and clearly influenced
by the stimulus duration but not markedly influenced by
stimulus frequency.
 The SP manifests itself as a shift in the CM baseline, the
direction of which is dictated by an interactive effect
between stimulus parameters (frequency and intensity)
and the location of recording electrode.

10.  Some of the components of SP represent inherent
nonlinearities associated with the transduction process
in the cochlea.
 Its sensitive to mechanical or electrical biasing.
(Durrant & Dallos 1974) .
 SP is enlarged in MD/ELH. (Schmidt et al., 1974)

11. Compound Action Potential (CAP):
 It is a summed response of numerous auditory nerve
fibers firing synchronously .
 It is an AC voltage, characterized by a series of brief
predominantly negative peaks.
 AP involves comparing its magnitude to that of SP in
patients suspected of having MD/ELH. (SP/AP
magnitude ratio). Enlarged magnitude ratio to click
stimulus is a positive finding for ELH.( Eggermont, 1976;
Coats, 1981)

13. RECORDING TECHNIQUES:
There are two general approaches for recording ECochG.
1. Transtympanic (TT)
2. Extratympanic (ET)
Transtympanic
Extratympanic

14.  TT ECochG is an invasive procedure that involves
passing a needle electrode through the TM to rest on the
cochlear promontory.
 During surgeries that expose the middle ear space, TT
recordings can also be made with a ball electrode on the
round window via the surgical field.
 Most audiologists who perform ECochG in the clinic
prefer ET approaches, wherein recordings are performed
with an electrode resting against the skin of the ear canal
or surface of the TM.
 For the latter recording site, the procedure is also
referred to as “Tympanic or TM ECochG” (Ferraro &
Ferguson 2000), even though this approach is still
considered to be ET.

15. ECOCHG RECORDING PARAMETER:
Parameter Selection
Electrode placement
Non-inverting Ear canal or TM or Promontary or RW
Inverting Contralateral mastoid
Ground Fpz (low forehead) or earlobe
Signal Averaging Setting
Time Base 5-10 ms
Amplification 50000-1,00,000 (ET), 5000 – 25000 (TT)
Bandpass Filter 5Hz – 3K Hz
Repetition 1000-1500 (ET), 100-200 (TT)
Stimuli
Type Broadband Clicks or Tone Bursts
Polarity Alternating
Repetition Rate 11.3/seconds
Level 85-95 dB HL
Inter electrode impedance Within + 2kohms

17. ElectrodeTypes& Placement:
1. Trans-tympanic electrodes (TT):
 Placement of needle on the promontory/ Round window.
Advantage:
 “Near field”, requiring relatively little signal averaging.
 Larger Amplitude
 Enhanced reliability
 Confidence in waveform analysis and in diagnosis of
Meniere’s disease.
Limitations:
 Invasiveness
 Assistance of physician and are therefore limited to medical
setting. Local anesthetics should be used (Beyond et al.,1998).

18. 2. Tiptrode Electrode:-
 It is inserted deeply in to the ear canal.
 Any discomfort to the patient should be monitored

19. 3. Tympanic Membrane Electrodes:
 This is designed to maximize response amplitudes while
minimizing clinical preparation cleansing and insertion
requirements.
o The electrode consists of a small gauge silver wire
enclosed within a flexible silastic tube and connected to a
soft foam sponge at the tip, which will be filled with
conductive gel.
 The electrode tip is made to contact with the TM.

20. 4. Subdermal Needle electrodes:
o During intraoperative neurophysiologic monitoring, sub
dermal needle electrodes are often used.
 It has the advantage of secure attachment to the patient
during surgical procedure and lower impedance.
 Two main health risks posed by needle electrodes are:
1. Spread of disease by an unsterilized needle.
2. Needle breakage.
 Should be done by appropriate medical professional.

21. COMPARATIVE ECOCHG FINDINGS WITH DIFFERENT
ELECTRODE TYPE AND LOCATION

22. ECOCHG WAVEFORM ANALYSIS & INTERPRETATION:
Three general ECochG analysis strategies
 A comparison of relative amplitude for the SP & AP
components and the SP/AP ratio.
 A comparison of the latency difference for the AP
component evoked with signals of rarefaction vs
condensation polarity.
 Calculation of the duration of the SP and AP
complex and calculation of area under SP and AP
components.

23. 1. Absolute latency:
 Absolute latency of components is a fundamental analysis
strategy.
 Identification of reliable AP component is the initial step in
waveform analysis of ECochG.
 In normal ears, latency is slightly shorter for AP components
evoked with rarefaction vs condensation signals.
2. Amplitude analysis:
o Amplitude can be measured from a single point or a baseline.
 Typically the peak in SP and AP amplitude in microvolt is
calculated from a baseline.
 This values used to calculate SP/AP magnitude ratio for click
stimuli, which is helpful to diagnose and monitor MD/ELH.
 SP/AP magnitude ratio for click stimuli ranges 0.16 to 0.31,
despite the use of different recording approaches in normal's.

25.  SP to tone burst persists as long as stimulus. AP in turn seen at
onset.
 SP magnitude is measured at the midpoint of the wave form with
reference to baseline magnitude. Thus the polarity of SP depends
on whether the voltage at midpoint is above (positive SP) or below
(negative SP) the baseline voltage.
 For both the recording TM and TT the polarities of the SPs at 500
and 8000 Hz are slightly positive where as negative SPs are seen at
1,2 and 4 KHz. This feature tends to vary across frequencies,
recording approaches and across subjects.

26.  MD the SP amplitude is enlarged .
 Rationale is that an increase in endolymph volume creates
mechanical /electrical biasing of vibration of the organ of corti to
which the SP is sensitive.
 Other factors such as biochemical and or vascular changes may
also be responsible for an enlarged SP in MD/ELH

27. 3. Duration analysis:
 Duration or width of the SP and AP components in combination, is a
measurement parameter for the diagnosis of MD (Ge & Shea
2002).
 The width of the SP & AP portion of the wave form, in ms, is defined
from the onset to the point where the wave form returns to the
baseline.
 The suspected mechanism underlying the prolongation in the
SP/AP width at least in MD is, slowed velocity of the traveling wave
within the cochlear secondary to restricted basilar membrane
movement with increased loading in ELH
(Ferraro & Tibbils 1999)

28. Clinical Application:
 Assessment of peripheral hearing loss.
 Enhancement of ABR Wave I.
 Diagnosis of MD
Diagnosis of Auditory Neuropathy.
Intraoperative monitoring
Recent Advancement in ECochG
Nowadays, ET ECochG is most often used as an
additional measurement in the diagnosis of patients
with Meniere’s Disease (MD).
It may also be a promising tool for the diagnosis and
evaluation of hearing loss in children with an auditory
neuropathy/dyssynchrony spectrum disorder (ANSD)
and potential candidates for a cochlear implant
(McMahon et al., 2009).

29. ECochG is an important tool for the diagnosis and evolution of ELH,
with an existing preference for the ET electrode positioning
(Lamounier et al., 2014). Increased SPs were observed with ET
ECochG in patients with MD (Kumar & Peepal 2012).
ECochG found its main application in the diagnostic evaluation of
Meniere's disease (MD). However, in the last decade, the focus has
shifted towards cochlear implantation (CI). In patients with residual
hearing after CI, combined electric and acoustic stimulation has
resulted in improved hearing and speech outcomes (Carlson et
al., 2021).

30.  During implantation, real-time ECochG offers an
opportunity to measure frequency specific CMs elicited
from a localized region in the cochlea as the surgeon
inserts the electrode array.
 In extracochlear ECochG recordings, the recording
electrode can be placed on the promontory, the stapes,
or the tympanic membrane.
 Intracochlear ECochG can be performed by inserting a
recording electrode into the cochlea or by using one of
the CI electrodes as the recording electrode. The loss of
intraoperative ECochG signal may indicate cochlear
trauma from electrode insertion.
 The ability to monitor cochlear trauma during CI
electrode placement holds promise to improve hearing
preservation outcomes, modify surgical techniques, and
change electrode design (Carlson et al., 2021).

31. REFERENCE:
 Bakhos, D., Marx, M., Villeneuve, A., Lescanne, E., Kim, S., & Robier, A.
(2017). Electrophysiological exploration of hearing. European annals of
otorhinolaryngology, head and neck diseases, 134(5), 325-331.
 Gibson, W. P. (2017). The clinical uses of electrocochleography. Frontiers in
neuroscience, 11, 274.
 Harris, M. S., Riggs, W. J., Giardina, C. K., O’Connell, B. P., Holder, J. T.,
Dwyer, R. T., & Adunka, O. F. (2017). Patterns seen during electrode
insertion using intracochlear electrocochleography obtained directly through
a cochlear implant. Otology & neurotology: official publication of the
American Otological Society, American Neurotology Society [and] European
Academy of Otology and Neurotology, 38(10), 1415.
 Choudhury, B., Fitzpatrick, D. C., Buchman, C. A., Wei, B. P., Dillon, M. T.,
He, S., & Adunka, O. F. (2012). Intraoperative round window recordings to
acoustic stimuli from cochlear implant patients. Otology & neurotology:
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Society [and] European Academy of Otology and Neurotology, 33(9), 1507.

32.  Pappa, A. K., Hutson, K. A., Scott, W. C., Wilson, J. D., Fox, K. E., Masood,
M. M., & Fitzpatrick, D. C. (2019). Hair cell and neural contributions to the
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