The 10/20 System

The 10/20 Locations
As I mentioned before, in neurofeedback, electrodes are placed on the scalp according to the internationally recognized 10/20 system. The name stems from the fact that all electrode placements are either 10% or 20% of the entire across-head distance away from each other. The placements of each electrode are chosen based on the underlying portion of cerebral cortex (the outer covering of the brain.) Below is a diagram of the cerebral cortex, which is divided into four lobes.

Frontal Lobe: associated with thinking, motor skills, and reasoning.
Parietal Lobe: associated with tactile sensory information (pressure, touch, pain), and processing of senses.
Temporal Lobe: associated with memory formation, sound/speech interpretation, and memory recall.
Occipital Lobe: associated with receiving and processing visual information from the eyes, as well as visual recognition of objects and colors.

These locations correspond with the first letter in all the 10/20 locations because they lie right underneath where the electrode is placed. Below is a map of the locations on the scalp. It is an aerial view of a person's head. In this case, the person is facing upwards (triangle = nose, ovals = ears)
 

As seen above, each electrode is placed 10% or 20% away from the next electrode (either vertically or horizontally). The name of each electrode begins with the first letter of the underlying lobe of the cerebral cortex. For example, P4 lies above the parietal lobe. The only exception is the Center (horizontal axis of symmetry over head). The second letter of the name is added based on where the electrode is placed on the head as a whole. Z is added if the electrode is on the head's vertical line of symmetry. Even numbers are added if the electrode is on the right hemisphere; odd numbers are added if the electrode is on the left hemisphere.

Here are some examples: 

Electrode C4: It must be placed on the horizontal axis of symmetry over the head, in the right hemisphere, and must be 20% away from Cz (the exact center of the head).

Electrode P3: It must be placed over the parietal lobes, in the left hemisphere, and 20% away from Pz (the location above the parietal lobe and on the vertical axis of symmetry of the head).

Using other locations as references, we can determine the harder, more difficult locations, like O2. Despite seeming like an inaccurate system, there is room for error. One has approximately a dime's area of error space around each location to place the electrode.

But why are these electrode locations even necessary? Even though the purpose of neurofeedback is to train all the brain's waves to the proper levels, certain problems will be located in specific areas of the brain. For example, a typical case of ADD will have excessive Theta amplitudes in the Frontal lobes (F locations). This slows the task-performing region of the brain, causing distractedness. 

Brainmap of ADD: The Z-score table on the left indicates that the child's Theta frequencies are 5+ standard deviations away from normal frequencies. I will later post how to read brainmaps and use them to diagnose mental disorders.

To treat this case of ADD, one must downtrain Theta waves in specifically those regions. Therefore, the electrode locations allow neurofeedback therapists to treat the problem area which is associated with the client's specific disorder. It minimizes training time and solves the problem effectively. In single channel, the main electrode is placed on a single electrode locations. In 19-channel neurofeedback, the electrode cap covers all 19 locations on the head, allowing analysis of all regions of the brain simultaneously. As a result, 19-channel is used for far more complex/intricate issues with a variety of indicators. A simultaneous view of all brainwave activity in every region of the brain allows for a better wholesome understanding of the patient's problem.

In a future post, I will discuss common mental problems and their associated brainwave patterns/defective brain regions.