Electroencephalographic Terms.2,3,4,5
15.11.2 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