The 10-20 System is an internationally accepted method for the placement of electrodes on the scalp in electroencephalography (EEG). This system ensures standardized, reproducible placement across patients and studies, which is essential for accurate monitoring of brain activity.
What Do the Letters Represent?
The letters in the 10-20 System correspond to specific regions of the brain. Each letter provides information about the underlying anatomical location where the electrode is positioned.
- F (Frontal lobe): Electrodes placed over the frontal lobe, associated with higher cognitive functions such as reasoning, problem-solving, and emotional regulation.
- C (Central region): Electrodes located over the central sulcus, between the frontal and parietal lobes. This area is involved in motor and sensory processing.
- P (Parietal lobe): Electrodes placed over the parietal lobe, which is responsible for spatial awareness, sensory integration, and perception.
- O (Occipital lobe): Electrodes in this region monitor visual processing, as the occipital lobe is responsible for interpreting visual information.
- T (Temporal lobe): Electrodes positioned over the temporal lobe, involved in auditory processing, language comprehension, and memory.
- Fp (Frontal pole): Electrodes at the most anterior part of the frontal lobe, often used for recording activity related to executive functions and attention.
- A (Auricular): Electrodes placed near the ears (e.g., A1 and A2), often used as reference or ground electrodes in EEG recordings.
- Z (Midline): Electrodes placed along the central sagittal plane of the head, denoting the midline of the brain (e.g., Fz, Cz, Pz).
What Do the Numbers Represent?
The numbers in the 10-20 System provide additional details about the electrode's position relative to the midline:
- Odd numbers: Electrodes located on the left hemisphere of the brain (e.g., F3, T5).
- Even numbers: Electrodes located on the right hemisphere of the brain (e.g., F4, T6).
- Z (Zero): Electrodes placed on the midline, dividing the left and right hemispheres (e.g., Cz, Fz, Pz).
Numbers also indicate proximity to the midline:
- Lower numbers: Closer to the midline (e.g., C1).
- Higher numbers: Farther from the midline (e.g., C5).
Why Is It Called the 10-20 System?
The name "10-20" reflects the standardized distances between adjacent electrodes. These distances are measured as 10% or 20% of the total front-to-back or side-to-side circumference of the head. This design ensures uniform electrode spacing regardless of head size, providing consistent and reproducible measurements.
Clinical Relevance of the 10-20 System
The 10-20 System is crucial for various clinical and research applications:
- Epilepsy Monitoring: Helps localize seizure activity, particularly focal seizures, by identifying specific regions of abnormal brain activity.
- Neurocognitive Studies: Electrodes over frontal regions (e.g., Fp1, Fp2) are used to study attention, decision-making, and executive function.
- Sleep Studies: Central electrodes (e.g., Cz) are essential for detecting sleep patterns, including sleep spindles and slow waves.
- Stroke and Brain Injury: Identifying damaged or affected regions by monitoring abnormal activity in corresponding electrode locations.
Advanced Systems Based on the 10-20 System
While the 10-20 System is widely used, it serves as the basis for more detailed systems, such as the 10-10 and 10-5 Systems. These advanced systems place additional electrodes for higher spatial resolution, often used in research or advanced clinical settings.
Note: The 10-20 System was first introduced by Herbert Jasper in 1958 and remains a global standard for EEG electrode placement.