1. AEPs Ahmed Khater, MD, PhD Ass. Prof. of audio-vestibular medicine
Consultant audiologist
Head of cochlear implant Program

2. Evoked potentials (EPs), or evoked responses, measure the electrophysiological responses of the neural cells to a variety of stimuli.

4. Audio-vestibular Evoked Potentials
From the vestibular nerve
From the OHCs
From the auditory nerve
VEMP
OAEs
Early, middle & late AEPs

5. Auditory evoked potentials span activity from the full length of the auditory pathway, from cochlear hair cells to cerebral cortex, as well as activity associated with cognitive processing auditory stimuli.

6. Indications Threshold detection For intra-operative monitoring
Diagnosis of site-of-lesion.
Neonatal screening
CAPD

7. AEP Early Middle Late (the first 10 ms), (10–80 ms)
(80 ms to 500+ ms).

10. Auditory brainstem response (ABR) peaks denoted by Roman numerals; I, II, III, IV, V, VI, VII
Middle latency response (MLR) are indicated by Po, Na, Pa, Nb, and Pb
Auditory late response (ALR) are indicated by P1, N1, P2, and N2.

11. AEP
Exogenous
Mesogenous
Endogenous

12. Exogenous: conditions external to the listener (e. g
Exogenous: conditions external to the listener (e.g. stimulus intensity or duration).
Mesogenous AEPs fall somewhere in between exogenous and endogenous as both external and internal conditions can affect the response eg. MLR.
Endogenous conditions internal to the listener (e.g. attention, vigilance)

13. Latency & Amplitude

14. The more caudal structures in the auditory nervous system would have shorter onset latencies than the more rostral structures. This latency increase for more rostral structures is the result of the finite action potential conduction velocity and the delay as the activity passes through chemical synapses.

15. Following presentation of an acoustic stimulus, We can record activity in the cochlea, auditory nerve, auditory brainstem, medial geniculate body, and auditory cortex.

16. Diagram of AEP Subject Traces Bioamplifier Acoustic stimulus Computer4-
Signal Averaging 1-
Filtering
Traces 2-
Artifact rejection 3-
A-C converter

17. Stimulus
1- Tone Burst
(long duration, long rise/fall times, and a very narrow spectrum)
2- Click
(short duration, very fast rise/fall times, and very broad spectrum).

18. Recording 1- Scalp preparation (Water) 2- Electrode connection:
- Noninverting lead is the positive or the active lead.
- Inverting lead is the negative or the reference lead
- The common lead is the ground

19. All are measured through scalp electrodes EXCEPT electrocochleography, the ECoG responses are typically NOT measured with scalp electrodes, but rather from electrodes placed in the ear canal, on or near the tympanic membrane, or on the promontory or round window of the inner ear

20. Any unwanted electrical activity…..Noise
Non-Biologic
Biologic
BioAmp.
Power
Muscle
EEG

21. Noise Reduction 1- Low electrode impedances.
2- Making the subject comfortable and encouraging them to sleep.
3- Filtering the output of the bioamplifier can reduce noise.
4- Signal averaging reduces unwanted background noise.
5- Light off.

22. Filters Band pass filter Band reject filter Low pass filter
High pass filter
Band pass filter
Band reject
filter

23. Electrocochleography (ECoG) refers to the responses from the cochlea and auditory nerve, using a recording electrode located in close proximity to the inner ear.
Labeling: CM, SP, AC

25. The auditory brainstem response (ABR), as its name indicates, is a series of five to seven peaks arising from auditory nerve and brainstem structures occurring within 10 ms of the onset of a moderate-intensity click stimulus.
Labeling: Wave I to VII

28. MLRs are usually recorded over a time window of 80 to 100 ms
MLRs are usually recorded over a time window of 80 to 100 ms. Generators are thought to include thalamus and auditory cortex.
Labeling: (e.g., Pa, Nb, etc.).

30. LLR: AEP responses occurring beyond roughly 75 ms.
These responses are commonly labeled with a capital N or P (e.g., P1 is the first positive SVP peak). OR N200 would be the negative peak with a mean latency of 200 ms.

32. There are differences in the responses to the frequent and infrequent stimuli used as an index of a cognitive construct that is related to attention.
If attending………P300
If not attending….MMN

35. VEMP

38. OAEs
Otoacoustic emissions (OAEs) are sounds measured in the external ear canal that reflect movement of the outer hair cells in the cochlea.

40. EP & MRI
The basic difference between the 2 studies is as follows:
MRI largely remains an imaging, structural, or anatomic test and therefore gives more accurate information about structural problems
EP testing assesses functionality and thus supplies information about the physiology of a certain anatomic pathway.
In some circumstances, MRI and EP studies may be complementary.

41. How often are we missing it?
If somebody comes in with DKA, head CT is probably not the first thing we would do
4 cases cited under Pubmed