Recommended Electrode Configurations

Module information
Modules	BESA Research Basic or higher
Version	5.2 or higher

General considerations

There are three important aspects for source analysis and source montages:

1) Electrodes should have equal spacing.

2) A row of inferior temporal electrodes on both sides is important to cover the lower head sufficiently, e.g. F11 (F9), A1, P11 (P9). The lower sites (F11, P11) at a 20% distance are preferable to sites at a 10% distance (F9, P9) from the standard row F7, T7, P7 (same applies to other side).

3) Electrodes should be symmetric between both hemispheres with a midline reference or an implicit reference (e.g. F3+F4). A recommended standard with 33 electrodes adds a midline reference Pz, and F11, A1, P11, FC1, FC5, CP1, CP5 and their homologues over the right hemisphere to the 19 electrodes of the 10-20 system (Fpz, Oz not included). For more details see BESA help chapter on Electrodes. When using caps with more electrodes (64 or 128) inferior electrode and equal spacing are similarly important.

In the following montage EEGxx the number xx indicates the number of electrodes.

EEG25 - Minimum 10-20 configuration including inferior electrodes

This covers the 19 standard 10-20 electrodes:

Fp1, Fp2, F7, F3, Fz, F4, F8 ....

plus 6 inferior electrodes on both sides:

F11, A1, P11, F12, A2, P12

with a recommended continuation of the 20% distances, i.e. use F11 instead of F9, P11 instead of P9, A1 instead of T9 to have a wider coverage of the inferior head. A1 / A2 may be replaced by T9 / T10 (or FT9 / FT10) for convenience and comfort.

Left: recommended configuration for 25 electrodes. Right: left temporal basal activity mapped with 25 electrodes.

EEG33 - Additional 10-10 electrodes within the major squares

To the above electrodes add the following 8 intermediate electrodes:

FC5, FC1, FC2, FC6, CP5, CP1, CP2, CP6

Left: recommended configuration for 33 electrodes. Right: left temporal basal activity mapped with 33 electrodes.

EEG35 - Additional supraorbital electrodes for better EOG separation

SO1, SO2

EEG37 - Wider inferior coverage at interlaced 20% distances

Continue 20% down from F7, FC5, CP5, P7 etc. and use the following 8 inferior electrodes instead of 6:

F11, FT9, TP9, P11, F12, FT10, TP10, P12

EEG41 – Improved frontal and occipital coverage

Additional electrodes halfway between Fz and Fp1 / FP2 and Pz and O1 / O2:

AF1, AF2, PO1, PO2

EEG43 – Inferior chain with 5 electrodes including A1 / A2

F11, FT9, A1, TP9, P11, F12, FT10, A2, TP10, P12

EEG43 represents the widest coverage with relatively even spacing.

Left: recommended configuration for 43 electrodes. Right: left temporal polar activity mapped with 43 electrodes.

EEG64-256

With 64 or more channel caps it is similarly recommended to use a sufficient number of inferior electrodes all around the head. At least 4 inferior temporal electrodes on each side and additional electrodes above or below the eyes (outside of the cap) are suggested.

We can recommend EGI Geodesic nets (64, 128, 256) and the equidistant EasyCap 61 with additional 3 electrodes for free placement around the eyes, or EasyCap 128 with nearly equidistant electrodes.

• EGI: Dense Array EEG
• EasyCap: EEG Recording Caps