The 10-20 system is a widely used method for electrode placement in electroencephalography (EEG). It is the basis for systematic brain mapping, providing a standardized approach to recording electrical activity. However, over time, there have been several extensions to this system that have been developed to enhance its precision and adaptability, particularly in clinical and research settings.

1. Introduction to the 10-20 System

The original 10-20 system is based on the proportional distance between certain landmarks on the scalp. The distances between the electrodes are designed as a percentage (10% or 20%) of the total front-back or left-right distance of the head. The electrodes are positioned along the sagittal, coronal, and transverse planes to cover the brain's major regions. The system was developed by the International Federation of Societies for Electroencephalography and Clinical Neurophysiology (IFSECN) in the 1950s.

2. Extensions to the 10-20 System

2.1. The 10-10 System

The 10-10 system is an extension of the 10-20 system that involves placing additional electrodes between the standard 10-20 electrode positions. In the 10-20 system, the distance between the electrodes is 10% to 20% of the total head circumference, and the 10-10 system places electrodes at the midpoints between these locations.

This extension allows for finer spatial resolution and improved accuracy in localizing brain activity. The 10-10 system is frequently used for high-density EEG recordings in research settings, allowing for a more precise study of brain function.

2.2. The 10-5 System

The 10-5 system further refines the electrode placement by adding even more points between the 10-10 electrodes. This system involves placing electrodes at 5% intervals of the total head circumference. The 10-5 system provides very high spatial resolution and is commonly used in research applications that require very detailed mapping of brain activity.

2.3. The 10-20-5 System

The 10-20-5 system combines the features of both the 10-20 and 10-5 systems. It uses the original 10-20 electrode placement but adds additional electrodes at 5% intervals between the primary 10-20 positions. This hybrid system balances ease of use with greater spatial precision, making it suitable for both clinical and research purposes.

2.4. The Extended 10-20 System (EEG Cap Systems)

Advances in EEG cap technology have led to the development of the extended 10-20 system, which integrates many more electrodes (up to 128 or 256 electrodes). These caps can cover a larger portion of the scalp, allowing for high-density EEG recordings that can capture more detailed spatial information. These systems are often used in modern clinical neurophysiology and functional neuroimaging.

2.5. The 10-20 System for Source Localization

Extensions to the 10-20 system have also been developed for source localization of brain activity. Using advanced signal processing techniques, such as EEG source imaging, the data collected from high-density electrode arrays (such as the 10-10 or 10-5 systems) can be used to localize neural sources with high precision. This is especially useful in clinical applications, such as identifying regions of the brain involved in epilepsy or planning for neurosurgery.

3. Other Related Systems and Technologies

3.1. High-Density EEG (HD-EEG)

In recent years, high-density EEG has become more common, employing dense arrays of electrodes (over 100 channels) to provide higher resolution and better temporal and spatial precision. This allows for detailed mapping of brain activity over more specific cortical areas, providing more accurate results for both clinical and research purposes.

3.2. 64-Electrode EEG Systems

In some settings, 64-electrode systems have been used as an alternative to the 10-20, 10-10, or 10-5 systems. These setups may offer sufficient coverage for many clinical applications, providing both precision and practicality.

4. Clinical and Research Applications

The extensions to the 10-20 system offer numerous benefits in both clinical and research settings:

  • Clinical Diagnostics: Extensions allow for more precise localization of epileptic foci, brain lesions, or functional impairments in patients.
  • Neurofeedback and Brain-Computer Interfaces: Higher electrode density provides more accurate control over neurofeedback applications or real-time brain activity tracking.
  • Neurosurgical Planning: The 10-10 and 10-5 systems are crucial in planning for surgeries, such as tumor resections or deep brain stimulation procedures, by providing detailed cortical maps.
  • Research on Brain Function: High-density EEG systems enable research in cognitive neuroscience, where precise mapping of brain areas is essential for understanding sensory, motor, and higher-order cognitive processes.

5. Conclusion

The extensions to the 10-20 system have significantly enhanced the capabilities of EEG for both clinical and research applications. From the 10-10 and 10-5 systems to the advanced EEG cap systems used for source localization and high-density recordings, these modifications provide higher spatial resolution, increased accuracy, and broader coverage of the scalp. As EEG technology continues to evolve, these extensions are helping to unlock new insights into brain activity, improving patient outcomes and advancing our understanding of the human brain.