An Electroencephalogram, commonly known as an EEG, is a medical procedure that measures and records the electrical activity of the brain. The fundamental purpose of an EEG is to identify patterns of brain activity that may indicate various neurological conditions. It provides a detailed look at the brain’s functional state by capturing faint voltage shifts from the scalp. The recorded brain waves appear as wavy lines, allowing medical professionals to assess normal or abnormal patterns of activity.
Essential Components of an EEG System
An EEG system relies on several specialized components to accurately capture brain signals. Electrodes, typically small, flat metal discs made of materials like silver, silver chloride, or gold, are placed on the scalp to detect the brain’s electrical signals. These electrodes are designed to provide a consistent, low-impedance connection to the scalp, ensuring clear signal transmission.
A conductive medium, such as a gel or paste, is applied with the electrodes to ensure optimal electrical contact between the electrode and the scalp. This gel helps reduce the electrical resistance, or impedance, of the skin. Without proper conductivity, the faint brain signals, which are in the order of microvolts, would be difficult to detect.
An EEG cap or headgear aids in the standardized placement of multiple electrodes across the scalp. These caps often have electrodes pre-positioned, simplifying the setup process and ensuring consistent coverage. The cap also helps secure the electrodes in place throughout the recording.
Following the electrodes, an amplifier boosts the weak electrical signals detected from the brain, making them strong enough for recording. The amplified signals are then sent to data acquisition software running on a computer. This software records, displays, and stores the raw EEG data, allowing for real-time monitoring and subsequent analysis by healthcare professionals.
Patient and Site Preparation
Before the EEG electrodes are applied, specific steps are taken to prepare the patient and their scalp. Patients are advised to wash their hair thoroughly the night before the appointment, avoiding any hair products like conditioners, gels, or sprays. Clean hair helps ensure better electrode contact and reduces potential interference with the electrical signals.
The scalp itself undergoes a cleaning process to further enhance signal quality. Technicians gently abrade the skin at each electrode site to remove impurities. This process is important for reducing the scalp’s electrical impedance, which can otherwise obscure the brain’s electrical activity.
Initial measurements are taken on the patient’s head to accurately determine the precise electrode locations. This involves measuring distances between specific anatomical landmarks. These measurements guide the placement of electrodes according to a standardized system, ensuring consistency across different recordings and patients.
Electrode Application and Connectivity
The International 10-20 System is a widely recognized method for standardized electrode placement on the scalp during an EEG. This system ensures consistent electrode positioning by basing locations on percentages of distances between key anatomical landmarks. Letters indicate brain regions (e.g., F for frontal, T for temporal, C for central, P for parietal, O for occipital), and numbers denote the hemisphere (odd for left, even for right), with ‘z’ for midline positions.
Individual electrodes, or a pre-wired EEG cap with embedded electrodes, are then carefully positioned on the scalp according to these measured points. If using individual electrodes, they are affixed with an adhesive. For caps, the technician ensures a snug fit, preventing movement that could introduce artifacts into the recording.
A conductive gel or paste is applied to each electrode site to ensure good electrical contact with the scalp. This gel fills any gaps between the electrode and the skin, further lowering impedance.
Before data acquisition begins, checking the electrode impedance is important. This measures the electrical resistance at each electrode site, confirming adequate connectivity. Acceptable impedance levels are typically below 5 kilohms (kΩ). If impedance is too high, the technician may reapply gel or gently abrade the skin again until optimal contact is achieved.
Monitoring and Data Acquisition
Once the EEG setup is complete and all electrodes show good connectivity, the data acquisition process commences. The patient is asked to relax in a comfortable position, with eyes closed, to minimize external influences on brain activity. Depending on the study’s purpose, they may also be instructed to perform specific tasks, such as opening and closing their eyes, or engage in mental activities.
Throughout the recording, a trained technician monitors the incoming EEG signals on a computer screen. This real-time monitoring allows them to ensure the quality of the signals and identify any artifacts. Artifacts are unwanted electrical signals that originate from sources other than the brain, such as muscle movements, eye blinks, or even electrical interference from nearby equipment.
The technician’s role includes making necessary adjustments to electrode placement or gel application if signal quality degrades. They also annotate the recording with notes about patient activities or any observed artifacts, which helps in the later analysis of the data. The continuous electrical activity from the brain is recorded and saved as a digital file for subsequent review and analysis by a medical professional.