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Contents

Evoked Potentials 

Chapter:
Nomenclature
Author(s):

Harriet S. Meyer

Evoked Potentials

2,3,14-17

Several types of evoked potentials (stimulated electrical signals) may be recorded: brainstem auditory evoked potentials (BAEPs), somatosensory evoked potentials (SSEPs, including various types such as the following, which are not mutually exclusive: short-latency, upper extremity, lower extremity, median nerve, posterior tibial nerve), and visual evoked potentials (VEPs, including pattern [PVEP] and flash [FVEP]). As in EEG, evoked potential testing uses recording electrodes and produces tracings.

Electrode terminology resembles that of EEGs (see above), with additional or modified electrodes such as the following,3 which may be used without expansion:

BAEP electrodes:

Ac

contralateral earlobe

Ai

ipsilateral earlobe

EAM

external auditory meatus

EAMc

contralateral EAM

EAMi

ipsilateral EAM

M1 M2

mastoid process

Mc

contralateral M

Mi

ipsilateral M

SSEP electrodes:

AC

anterior cervical

C1′, C2′, C3′, C4′

near EEG C1, C2, C3, C4

C2S, C5S

C2, C5 spinous processes

Cc

contralateral C3′ or C4′

Ci

ipsilateral C3′ or C4′

CP

midway between C3 or C4 and P3 or P4

CPc

contralateral CP

CPi

ipsilateral CP

Cz′

near 10–20 Cz

EP

Erb point

EP1, EP2

left and right EP

EPi

ipsilateral EP

Fpz′

near EEG Fpz

IC

iliac crest

L2S, L3S

L2, L3 spinous processes

LN

lateral neck

LNi

ipsilateral LN

PFd, PFp

popliteal fossa (distal, proximal)

REF

reference

T6S, T10S, T12S

T6, T10, T12 spinous processes

VEP electrodes:

I

inion

LO

left occipital

LT

left posterior temporal

MF

midfrontal

MO

midoccipital

MP

midparietal

RO

right occipital

RT

right posterior temporal

V

vertex

Waveforms recorded in evoked potential testing are identified with P for positive or N for negative plus a number indicating milliseconds between stimulus and response in normal adults:

VEP:

N75, N100, N155, P75, P100, P135

SSEP:

N9, N11, N13, N15, N18, N20, N34, N35, P9, P11, P13, P15, P27, P37

SSEPs were…recorded from the brachial plexus (Erb potential), cervical spine at C2 (N13), and the contralateral parietal area (N19) with a frontal (Fz) reference.

SSEPs showed normal Erb point and cervical potentials and significant delay of scalp components (N20 latency >>3 SDs, N13-N20 central conduction time >3 SDs, bilaterally).

Persistent delay of the P100 wave of the pattern-reversal VEP after an episode of optic neuritis is considered to be compatible with residual demyelination within the optic nerve.

An additional SSEP wave is the LP (lumbar potential).

 Other waves, eg, in BAEP, are designated with roman numerals:

I through VII

vertex-positive waves

I′ through VI′

vertex-negative waves

BAEPs of the proband showed normal wave I, increased latency of waves II and III (>3 SDs), and absent IV and V components despite normal hearing acuity.

I-III interpeak interval

V/I amplitude ratio

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