Understanding EEG Montages

EEG (Electroencephalography) signal monitoring involves recording electrical activity from the scalp through an array of electrodes arranged in specific patterns, called montages. These montages determine how signals from the electrodes are displayed and interpreted. Here's a structured overview:

Electrode Placement

  • Electrodes are placed on the scalp based on standard systems, such as the 10-20 system, which ensures consistent and reproducible placement.
  • Each electrode is labeled with a letter and a number:
    • Letters indicate the brain region (e.g., F for frontal, T for temporal).
    • Numbers differentiate the hemisphere (odd numbers for left, even numbers for right).

Montage Types

Bipolar Montage

  • Electrodes are connected in pairs, with each pair representing the difference in electrical potential between two adjacent electrodes.
  • Highlights local activity and minimizes external noise.
  • Commonly used for detecting focal abnormalities.

Referential Montage

  • Each electrode's signal is referenced to a common electrode (e.g., earlobe or mastoid).
  • Provides a broader view of the electrical activity across the brain.
  • Suitable for detecting generalized abnormalities.

Constructing Montages

  • The choice of montage depends on the clinical or research objective.
  • Software in EEG machines or systems allows users to configure montages by connecting electrodes virtually.
  • Some examples:
    • Longitudinal Bipolar: Connections along the anterior-posterior axis.
    • Transverse Bipolar: Connections along the left-right axis.
    • Average Referential: All electrodes referenced to the mean signal of all electrodes.

Getting Started with EEG Interpretation

Familiarize with Normal Patterns

  • Learn common waveforms (e.g., alpha, beta, theta, delta rhythms) and their typical distributions.

Identify Abnormalities

  • Look for atypical patterns, such as spikes, sharp waves, or slowing.

Understand Artifacts

  • Differentiate between physiological (e.g., muscle activity) and non-physiological (e.g., electrical interference) artifacts.

Use Tools

  • Employ software for visualization and analysis.
  • Adjust filters and montages to enhance signal clarity and interpretation.