Chewing and hypoglossal (tongue) artifacts are common but distinct types of artifacts in EEG recordings. While they can sometimes be confused with other types of physiological or pathological activity, they have unique features that make them identifiable. Below is a detailed explanation of each artifact:

1. Chewing Artifact

Source: The chewing artifact originates from muscle activity in the temporalis muscle (a muscle involved in chewing).

Appearance: This artifact appears as intermittent bursts of generalized, very fast activity, typically in high frequencies (often in the gamma or high-beta frequency range).

Key Characteristics:

  • Sudden onset: The activity begins abruptly in correlation with the physical act of chewing or jaw movements.
  • Intermittent: The activity occurs in bursts, following the chewing cycle.
  • High-frequency activity: The artifact is much faster than typical brain activity, showing bursts of energy in higher frequencies.

Differentiation from Other Artifacts:

  • Distinct Morphology: Chewing artifact doesn’t resemble other common EEG patterns like generalized periodic fast activity (GPFA) or seizures. GPFA tends to have a slower rhythm and lower amplitude compared to chewing artifact.
  • Video Correlation: This artifact can be easily confirmed by video recordings, where you can visually observe the patient chewing.
  • Precaution: Be cautious not to confuse chewing artifact with other fast rhythms, like seizures, as they may share some frequency characteristics but differ in morphology.

2. Hypoglossal (Tongue) Movement Artifact

Source: The hypoglossal artifact arises from movement of the tongue and can cause muscle contractions that are detected by the EEG.

Appearance: The artifact appears as slower, diffuse delta frequency activity, with broad, rhythmic waves covering a large part of the EEG.

Key Characteristics:

  • Delta frequency: The artifact produces lower-frequency activity, typically within the delta or theta range (1-4 Hz).
  • Diffuse activity: The artifact is spread over a large region of the EEG, and its pattern tends to be uniform across the recording.
  • Rhythmicity: The tongue's movements create organized and repetitive patterns, which are more sustained than what is seen during normal sleep.

Reproducibility:

  • Movements: The hypoglossal artifact is reproducible. Asking the patient to move their tongue or say a certain phrase (like "la la la") can often induce the same pattern in the EEG.

Differentiation from Pathology:

  • Rhythmicity vs. Seizure Activity: Hypoglossal artifact can resemble ictal (seizure-related) patterns, but it lacks the evolving features of seizures, such as changes in frequency, amplitude, or location over time.
  • No Evolution: Unlike seizures, this artifact doesn’t evolve in terms of rhythm, location, or amplitude, making it easy to distinguish.

Summary

Chewing Artifact: Characterized by fast, intermittent bursts of high-frequency activity due to temporalis muscle contractions. It is easy to distinguish, especially with video correlation.

Hypoglossal Artifact: Results from tongue movement and presents as slower, diffuse delta frequency activity. It is reproducible and rhythmic but lacks the evolving characteristics seen in seizures.

In clinical practice, distinguishing these artifacts from real pathology is critical. Video studies or verbal instructions to the patient can help confirm whether the artifact is related to chewing or tongue movements rather than brain pathology.