- EEG Lead System Definition: The EEG lead system is defined as the placement of electrodes on the scalp using the 10-20 system, recommended by the International Federation of EEG society.
- Electrode Placement: Electrodes are positioned at specific percentages along the nasion-inion line and temporal lobes to capture brain activity accurately.
- EEG Recording Setup: An EEG recording setup involves a 21-electrode system connected to an 8-channel selector and a differential amplifier, leading to a signal processing unit.
- Noise Reduction: Differential amplifiers are essential in reducing 50 Hz noise from AC interference in EEG recordings.
- Recording Modes and Filters: The setup includes low pass, high pass, and band pass filters, and uses Unipolar, Average mode, and bipolar recording methods for EEG recording.
EEG Lead System
The International Federation of EEG Society recommends the 10-20 electrode placement system for EEG recording. This system uses silver/silver chloride electrodes as surface electrodes. The distances between electrodes on the scalp are set at 10% and 20% of the distance between specific points.
Nasion and Inion are two reference points on the scalp, near the ear lobes. The distance between them is divided into five parts over the head. Electrodes are placed at the frontal, central, and parietal points along this line.
They are placed at a distance of 10%, 20%, 20%, 20%, 20% and 10% of this length. Now, similarly nasion – inion distance is measured along the temporal lobes and five electrode are placed as two in frontal, 2 in temporal and 1 in occipital lobes respectively. They are also placed at a distance of 10%, 20%, 20%, 20%, 20% and 10% of this length on either side.
Finally, six more electrodes are placed around the periphery: two in the frontal, two in the central, and two in the parietal regions. This setup includes 19 electrodes on the scalp and one reference electrode at the ear lobe, known as the 10-20 EEG system.
EEG Recording Setup
This setup uses a 21-electrode system connected to an 8-channel selector. The output from the selector goes to a differential amplifier bank, which includes preamplifiers to reduce noise. The 50 Hz noise from AC interference is minimized by the differential amplifier. The processed output is then sent to a signal processing unit and displayed on the display unit.
This system helps to record the potentials generated from the sensory parts of the brain. To achieve this, output unit is connected with audio stimulus, visual stimulus and touch stimulus. It can also measure the time delay between stimulus and response from brain.
Additionally, the system includes a filter bank with low pass filters, high pass filters and band pass filters to remove noise from brain waves. The output can be recorded using either a pen recorder or a CRO. The three recording modes used are Unipolar, Average mode, and bipolar recording.
Applications of EEG
- Epilepsy diagnosis.
- Anesthetic level.
- Brain injury.
- Monitoring during surgery.
