Signal Artifacting
Raw EEG is highly susceptible to non-cerebral electrical activity. Manual artifact rejection is a critical step prior to quantitative analysis.
The Danger of Automated Rejection
While Independent Component Analysis (ICA) can mathematically isolate eye blinks, manual pruning by a trained technician remains the gold standard. Automated systems frequently discard legitimate fast-wave cortical activity (Beta) by mistaking it for high-frequency muscle tension (EMG).
Primary Contaminants
EMG (Muscle Tension)
Characterized by high-frequency, high-amplitude spikes, particularly in temporal leads (T3/T4) due to masseter (jaw) clenching. It heavily contaminates Beta and High-Beta band analysis.
EOG (Eye Blinks)
Presents as massive slow-wave (Delta/Theta) deflections in the frontal leads (Fp1/Fp2). Must be manually spliced out to prevent false-positive frontal slowing diagnoses.
EKG (Cardiac Pulse)
R-wave intrusion can occur, appearing as a rhythmic spike across all channels, more prominent in individuals with short, thick necks.
Artifacting Methodology (N=340 Study)
In our clinical review of 340 consecutive QEEG maps, manual artifacting resulted in a 14% shift in Z-score severity compared to purely automated ICA pruning. This shift frequently altered the primary treatment protocol.
Common Mistakes
- Glossing over drowsiness Drowsiness induces Alpha dropout and Theta elevation, often misread as ADHD.
- Ignoring glossokinetic artifact Tongue movement creates massive slow-wave distortion across the entire cortex.