10–20 system (EEG)

21 electrodes of International 10-20 system for EEG

The 10–20 system or International 10–20 System is the most common method used for the application of electroencephalographic electrodes in both research and clinical settings. This system is based on the relationship between the location of an electrode and the underlying area of the cerebral cortex. Its standardized nature allows for consistency in studies and in the practice of neurology, making it a fundamental technique in the field of neuroscience.

Overview

The 10–20 system is an internationally recognized method to describe and apply the location of scalp electrodes in the context of an EEG examination. This method ensures that the naming of electrodes is consistent across different laboratories and studies. The system is based on the idea that the skull circumference can be divided into sections based on certain percentages of distance from prominent skull landmarks, namely the Nasion, Inion, and the preauricular points.

Electrode Placement

In the 10–20 system, electrode placement is determined by dividing the distance between these anatomical landmarks into 10% and 20% increments. For example, the distance between the nasion and inion is measured, and electrodes are placed at 10%, 20%, up to 90% of this distance. Similarly, measurements are taken and electrodes placed between the left and right preauricular points. This results in a series of standard electrode positions, each with a designated label.

Electrodes are named according to their position over the cerebral cortex. The letter reflects the underlying brain area (F for frontal, T for temporal, C for central, P for parietal, and O for occipital lobes), while the number indicates the hemisphere (odd numbers for the left hemisphere, even numbers for the right, and z (zero) for midline electrodes).

Clinical and Research Applications

The 10–20 system is widely used in both clinical and research settings. Clinically, it is employed in the diagnosis and treatment of neurological conditions such as epilepsy, sleep disorders, and brain injuries. In research, it facilitates the study of brain function, cognitive processes, and the effects of various interventions on brain activity.

Advantages and Limitations

One of the main advantages of the 10–20 system is its standardization, which allows for comparability across different studies and clinical assessments. However, it has limitations, including the fact that it does not cover the entire scalp, potentially missing cortical areas of interest. Additionally, the system assumes a certain level of skull and brain symmetry, which may not be accurate for all individuals.

Extensions and Variations

To address some of the limitations of the 10–20 system, extensions such as the 10–10 and 10–5 systems have been developed. These systems offer a more detailed mapping of the scalp by increasing the number of electrodes, thereby providing a finer resolution of brain activity.

Conclusion

The International 10–20 System remains a cornerstone in the field of electroencephalography, providing a standardized framework for electrode placement. Its widespread adoption underscores its importance in ensuring consistency and comparability in EEG studies and clinical practice. Despite its limitations, the system's extensions and variations continue to enhance its applicability and precision in measuring brain activity.