EEG Frequency Range on Polysomnography
The frequency range for EEG on a polysomnogram spans approximately 1 to 100 Hz, with clinically relevant activity primarily captured between 1-30 Hz for standard sleep staging. 1
Standard Frequency Bands Used in PSG
The EEG recorded during polysomnography is analyzed across several distinct frequency bands, each with specific physiological significance:
Delta (1-4 Hz): Represents slow wave activity characteristic of deep sleep (N3/slow wave sleep); abnormally prominent delta during wakefulness indicates brain dysfunction 1
Theta (4-7 Hz): Small amplitude during normal waking states; increased theta may indicate drowsiness or pathology 1
Alpha (8-12 Hz): The dominant posterior rhythm during relaxed wakefulness with eyes closed; subdivided into low-frequency alpha (8-10 Hz) reflecting low arousal and high-frequency alpha (10-13 Hz) associated with perceptual processes 1
Beta (12-30 Hz): Low-frequency beta (12-20 Hz) reflects low levels of somatomotor and memory processes; high-frequency beta (20-30 Hz) appears during active cognitive states 1
Gamma (30-70 Hz and higher): Associated with active sensorimotor and cognitive processing, prompted by cholinergic inputs and thalamocortical projections 1
Technical Recording Specifications
The detectable frequency range extends to approximately 100 Hz due to the high temporal resolution (<1 ms) of modern EEG recording systems, though skull and scalp resistance primarily limit clinically useful signals to the 1-100 Hz range. 1
Standard PSG typically utilizes 4-6 channels of EEG for basic sleep staging, though extended 18-channel montages following the 10-20 system can be employed when evaluating for nocturnal seizures or focal epileptiform activity 2
The American Academy of Sleep Medicine recommends specific electrode placements including C4-M1, F4-M1, and O2-M1 as primary signals for sleep analysis 3
Clinical Relevance for Sleep Staging
For routine sleep stage scoring, the most critical frequencies are delta (1-4 Hz) for identifying slow wave sleep, theta (4-7 Hz) for drowsiness, alpha (8-12 Hz) for wakefulness, and sleep spindles (11-15 Hz) for N2 sleep identification. 4
Sleep spindles occur at two distinct frequencies in children: 11.0-12.75 Hz over frontal regions and 13.0-14.75 Hz over centroparietal regions 4
K-complexes and vertex sharp waves, essential for N2 sleep scoring, contain mixed frequency components but are best identified in the delta-theta range 4
Important Caveats
The frequency content of EEG varies significantly with age—the dominant posterior rhythm increases from 3.5-4.5 Hz at 3-4 months post-term to 8-10 Hz by age 3 years, reaching adult values of 8-12 Hz in adolescence. 4 This developmental consideration is critical when interpreting pediatric polysomnograms, as age-inappropriate frequencies may indicate neurological dysfunction even when the absolute frequency values fall within the standard 1-100 Hz recording range.