Electroencephalography (EEG) is a technique used to record electrical activity in the brain. While standard EEG primarily focuses on the scalp for electrode placement, electrodes may also be placed on the cheek in specific cases to enhance diagnostic accuracy or obtain additional physiological information. Below is a detailed, step-by-step explanation of the purpose of cheek electrode placement in EEG, progressing from beginner concepts to advanced insights.

1. Basic Concepts of EEG Electrode Placement

  • EEG Fundamentals: EEG measures electrical potentials generated by neuronal activity in the brain, specifically cortical neurons. Standard electrode placement typically follows the 10-20 International System.
  • Standard Electrode Sites: Most electrodes are placed on the scalp to record cortical activity. However, certain non-standard sites, like the cheek, are used in specialized contexts.

2. Why Place an Electrode on the Cheek?

Placing an electrode on the cheek is not standard practice in routine EEG. However, it has specific applications in advanced diagnostics and research:

  • Monitoring Muscle Activity: The cheek contains facial muscles (e.g., the masseter and zygomaticus) whose activity can cause artifacts in EEG recordings. Cheek electrodes help detect and differentiate electromyographic (EMG) artifacts.
  • Eye Movement Artifact Identification: Electrodes near the eyes, such as on the cheek, can record signals related to eye movements and blinks, which are common sources of contamination in EEG data.
  • Supplemental Polysomnography Data: In sleep studies, cheek electrodes may assist in monitoring REM sleep by capturing facial muscle tone and activity changes.
  • Localizing Seizures: In rare cases, electrodes on the cheek are used to investigate seizures originating from the facial motor cortex or the peri-orbital region.

3. Clinical Applications

  • Sleep Studies: Cheek electrodes are commonly used in polysomnography (PSG) to identify rapid eye movement (REM) sleep by tracking muscle activity.
  • Artifact Rejection in Cognitive Research: In studies requiring clean EEG data, cheek electrodes are used to track and remove facial muscle artifacts.
  • Specialized Epilepsy Monitoring: In specific epilepsy cases, cheek electrodes provide additional localization information for seizures with atypical presentations.

4. Technical Insights

  • Electrode Placement: The cheek electrode is typically placed near the zygomatic arch or lower part of the maxilla, ensuring minimal discomfort to the patient.
  • Signal Interpretation: Cheek electrodes primarily record high-frequency muscle activity rather than cortical brain signals. Advanced filtering techniques are often applied to distinguish artifacts from true EEG signals.
  • Advanced Artifact Processing: Techniques like Independent Component Analysis (ICA) leverage cheek electrode data to remove non-cortical artifacts from scalp EEG recordings.

5. Peer-Reviewed Evidence

Multiple studies validate the utility of cheek electrodes in EEG:

  • A study in the journal Clinical Neurophysiology (2018) demonstrated the value of cheek electrodes in artifact rejection during high-density EEG recordings.
  • Research published in Sleep Medicine Reviews (2020) highlighted the role of cheek electrodes in enhancing REM sleep detection during polysomnography.
  • An article in Epilepsia (2016) described the use of cheek electrodes for improved localization of seizures in patients with facial motor symptoms.

6. Expert-Level Insights

At an advanced level, the cheek electrode data can be integrated with machine learning algorithms to automate artifact rejection and improve EEG signal quality. Additionally, research into non-invasive brain-computer interfaces (BCIs) has begun to explore the role of cheek electrodes in capturing supplementary signals for more robust device control.

Conclusion

While not part of standard EEG protocols, placing an electrode on the cheek serves specific diagnostic and research purposes, such as identifying artifacts, aiding sleep studies, and localizing seizures. Understanding the role of these electrodes is crucial for optimizing EEG data quality and interpretation.