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Electroencephalographic Terms

Chapter:
Nomenclature
Author(s):

Harriet S. Meyer

Electroencephalographic Terms

2,3,4,5

Guidelines for electroencephalography (EEG) are available through the American Clinical Neurophysiology Society (formerly the American Electroencephalographic Society; http://www.acns.org)6 and at the International Federation of Clinical Neurophysiology website (IFCN; http://www.ifcn.info; formerly the International Federation of Societies for Electroencephalography and Clinical Neurophysiology).7

The International 10–20 System specifies placement of electrodes used in electroencephalography. The 10–20 System, which originated in the 1950s,8,9 is so named because electrodes are spaced 10% or 20% apart along the head (Figure 8).

Figure 8. Electroencephalographic lead positions, from EEG in Clinical Practice, 2nd ed, by J. R. Hughes, Boston, MA, Butterworth-Heinemann; 1994:2. Reprinted by permission of Elsevier.

The terms used in the 10–20 System are widely used and recognized. They are systematically derived, as follows:

  • Letters refer to anatomic areas (primarily of the skull, which do not necessarily coincide with the brain areas from which the electrodes register electrical activity).

  • Odd numbers are for electrodes placed on the left side, even numbers are for electrodes placed on the right side, and the letter z (“zero”) is for midline electrodes.

Electrode Designation

Location

A1, A2

earlobe

Cz, C3, C4

central

F7, F8

lateral frontal (anterior temporal)

Fp1, Fp2

frontal pole or prefrontal

Fz, F3, F4

superior frontal

O1, O2

occipital

Pz, P3, P4

parietal

T3, T4

midtemporal

T5, T6

posterior temporal

Additional electrodes and other placement systems may be used, for instance, the “modified combinatorial nomenclature” also known as the extended 10–20 electrode system or the 10% system, which adds electrodes at intermediate 10% positions.7,10-12 The same electrode may have a different name in the 10–20 and the 10% systems.4 The added electrodes result in additional numeric designations for existing regional electrodes (eg, C5, F10) and in new letters or letter-number combinations, as in the following examples:

Electrode Designation

Location

AFz, AF3, AF4, AF7, AF8

anterior frontal

C1, C2, C5, C6,

centrotemporal

CPz, CP1-CP6

centroparietal

FCz, FC1-FC10

frontocentral

Fpz

midprefrontal

FT7, FT8, FT9, FT10

frontotemporal

Iz

inion

Nz

nasion

Oz

midoccipital

P1, P2, P5-P10

parietal-posterior temporal

POz, PO3, PO4, PO7, PO8

parieto-occipital

Sp1, Sp2

sphenoidal

T1, T2

true anterior temporal

T7-T10

centrotemporal

TP7-TP10

temporal-posterior

Neonatal electrodes may be placed differently (eg, the 12.5% to 25% system of the Children’s Hospital of British Columbia) and may (or may not) have different designations,4 eg:

LaF

left anterior frontal

LaT

left anterior temporal

LFC

left frontocentral

LO

left occipital

LP

left parietal

LST

left superior temporal

RaF

right anterior frontal

RaT

right anterior temporal

RFC

right frontocentral

RO

right occipital

RP

right parietal

RST

right superior temporal

In figures showing EEGs, electrode symbols usually will be paired. Usually, the symbols will be beside and to the left of each channel of the tracing but may be above and below each channel with connecting lines. Authors should include with tracings a time marker and an indicator of voltage, as in the top tracing (Figure 9).

Figure 9. Sample electroencephalographic tracings (schematic).

Descriptions of EEG potentials include many qualitative terms for waveforms and frequencies. The following are a few of numerous descriptive terms (note that Greek letters are spelled out):

alpha rhythm, beta activity, polymorphic delta activity, sleep spindles, spike-wave complexes, paroxysms, spikes, sharp waves, delta brush, frontal sharp transient, mu rhythm, lambda waves

A comprehensive glossary of EEG terms has been provided by the IFCN.13

Frequency is given per second (/s). For cycles (c) per second, hertz (Hz) is preferred to c/s (see 18.1, Units of Measure, SI Units):

10-Hz alpha activity

a theta frequency of 5 to 7.5 Hz

15-Hz spindles

60-Hz artifact

background rhythm of 8 to 10 Hz

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