The"10-20System" of Electrode Placement

The 10-20 System of Electrode Placementis a method used to describethe location of scalp electrodes. These scalp electrodes are used torecord the electroencephalogram (EEG) using amachine called an electroencephalograph. The EEGis a record of brain activity. This record is the result of the activity ofthousands of neurons in the brain. The pattern of activity changes withthe level of a person's arousal - if a person is relaxed, then the EEG hasmany slow waves; if a person is excited, then the EEG has many fast waves. The EEG is used to record brain activityfor many purposes including sleep research and to help in the diagnosis ofbrain disorders, such as epilepsy. A sampling of brain waves from ScientificAmerican.

Anelectroencephalograph

The 10-20 system is based on the relationship between the location ofan electrode and the underlying area of cerebral cortex. Each point onthis figure to the left indicates a possible electrode position. Eachsite has a letter (to identify the lobe) and a number or another letter toidentify the hemisphere location. The letters F, T, C, P, and O stand forFrontal, Temporal, Central, Parietal and Occipital. (Note that there isno "central lobe", but this is just used for identification purposes.) Even numbers (2,4,6,8) refer to the right hemisphere and odd numbers(1,3,5,7) refer to the left hemisphere. The z refers to an electrodeplaced on the midline. Also note that the smaller the number, the closerthe position is to the midline. Nasion - point between the forehead andnose. Inion - Bump at back ofskull

Used with Permission

For more on the EEG, see:

1. Electroencephalography
2. EEG and Evoked Potentials

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