Sleep Technology: Recording, Scoring, and Artifact Control
What the exam is really testing
Sleep technology questions reward a candidate who understands the chain of measurement: sensor placement, signal conditioning, display settings, and scoring rules. Know the standard EEG derivations (F4-M1, C4-M1, O2-M1) and why occipital channels matter for alpha and frontal channels for slow waves. Understand EOG as a dipole: conjugate eye movements produce out-of-phase deflections on left and right EOG, while EEG artifact appears in phase. EMG belongs on the chin for wake/N1 tone and on the legs for periodic limb movements.
Concepts to own
- Filter and display settings: sensitivity, time base (30 s/page), low- and high-frequency filters. A question may ask why a slow wave "disappears"-often a high-frequency filter set too low or sensitivity too low.
- Impedance and electrode care: high impedance invites 60 Hz artifact and mismatch; know the difference between 60 Hz interference and sweat artifact (slow sway).
- Artifact recognition: EKG artifact in EEG, pulse artifact, snore artifact on chin EMG, and respiratory artifact on EEG.
- Scoring rules: sleep onset, stage transitions, arousal duration, and the epoch rule-score the stage occupying the majority of the epoch.
Traps
Candidates confuse amplitude criteria with frequency criteria; mix up which channel defines alpha; and forget that an arousal requires an abrupt shift with at least 3 seconds of faster EEG after at least 10 seconds of stable sleep. Another trap: assuming an artifact always invalidates an epoch-often it can be identified and the epoch still scored.
Rule of thumb
If a signal looks wrong, check the physical cause first (electrode, impedance, filter), then the physiologic cause, then the display settings. Worked example: a 30-second epoch shows 12 seconds of alpha in O2-M1 with eyes closed-score Wake, because alpha occupies the majority of the epoch.