Electroencephalography (EEG) is a non-invasive method that records the brain’s electrical activity. This technique involves placing small metal discs, called electrodes, onto the scalp to detect the electrical signals produced by neurons. These signals, often referred to as brain waves, provide insights into brain function and can help in diagnosing various neurological conditions.
Common Electrode Counts
The number of electrodes used in an EEG recording varies by examination purpose, with common ranges for different applications. Routine clinical EEGs typically utilize a smaller set of electrodes, often around 19 to 21. This configuration is sufficient for diagnosing conditions like epilepsy and assessing overall brain function in a clinical setting.
Research applications frequently employ a higher number of electrodes to gather more detailed data. These setups might include 32, 64, or even 128 electrodes. The increased number of electrodes allows for a more comprehensive mapping of brain activity and greater spatial resolution, beneficial for understanding complex brain processes or specific studies. The choice of electrode count balances the need for detailed information with practical considerations such as setup time and cost.
The 10-20 Placement System
To ensure consistency and comparability across different recordings, a standardized method for electrode placement is widely used, known as the International 10-20 system. It provides a reliable framework for positioning electrodes on the scalp, regardless of head size or shape. The “10” and “20” refer to the percentages of the total distance between specific anatomical landmarks on the skull, such as the nasion and inion. These measurements guide the placement of electrodes in a proportional grid-like pattern.
Electrodes in the 10-20 system are identified by letters that correspond to the underlying brain regions, such as F for frontal, T for temporal, C for central, P for parietal, and O for occipital. Numbers are used to indicate the hemisphere, with odd numbers typically on the left side, even numbers on the right, and ‘z’ for electrodes along the midline. This systematic nomenclature allows for precise and reproducible electrode positioning, which is important for accurate interpretation of EEG data. Extensions like the 10-10 system, which places electrodes at 10% intervals, allow for additional sites and higher resolution when needed.
High-Density EEG Configurations
High-density EEG (HD-EEG) systems employ a significantly larger number of electrodes than standard setups. These configurations typically use 64, 128, 256, or even more electrodes, with some systems capable of using up to 512 electrodes. The primary advantage of HD-EEG is its ability to provide enhanced spatial resolution, meaning it can capture more localized and detailed brain activity. The closely spaced electrodes allow for a finer mapping of electrical signals across the scalp, which can reveal activity that might not be detectable with fewer electrodes.
This increased detail is particularly beneficial in research and specialized clinical applications, such as precisely locating seizure origins. Combined with electrical source localization, HD-EEG can estimate where electrical activity originates within the brain. This provides a more comprehensive understanding of brain function and aids in surgical planning or the diagnosis of complex neurological disorders. The benefits of high-density systems include improved signal-to-noise ratio and greater flexibility in source localization, making them valuable for in-depth brain research.