The 10-20 and the Queen Square electrode placement systems both assume a relatively normal head shape. Individuals with very unusual shapes are more likely to require investigations and procedures that require the placement of scalp electrodes. What approaches are people using to compensate for the head shape?
Which electrode placement system you choose will depend on what you observe as "very unusual"about the patients head shape.. Since the international 10-20 and 10-10 systems are based on % distances between external landmarks (nasion, inion, ante-tragal points etc). they can be used for almost all heads. The 10-10 system. along with a verbal description of the head shape, will nearly always serve nicely
The head that provoked this question was strikingly asymmetrical in each plane. A second head in the same week appeared to have significant amounts of fluid in pockets under the skin..
I would still try to place electrodes symmetrically respect to main external landmarks to allow inter-hemispheric comparisons
For those who are interested we examined the brain post-mortum and observed a very asymmetric brain.
There isn't really a simple way to compensate for this. Best approach, without developing a compensation placement system, would be to maintain use of the standardised approach. Luckily EEG does not record directly under the surface so it is still likely that you would pick up a reasonable amount of data from the sources that you assume to be recording from.
The international 10-20 system as it is purely based on distances and not on the measure of the head.
Any other way found recently Jonathan A Norton
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