Table 1.
Sleep-Related EEG Activity Stage
| EEG frequency | Features | Key neural pathways | Hypothesized function | % of TST in healthy adults | |
|---|---|---|---|---|---|
| Wakefulness | Alert- beta Relaxed- alpha (8–13 Hz) |
||||
| N1 | Theta (4–7 Hz) | Lightest sleep stage, slow eye movements | Cortex | Transitional state | 2–5% |
| N2 | Theta (4–7 Hz) | K-complex, spindles | Thalamo-cortical circuit | 45–55% | |
| N3 | Delta (0.5–2 Hz) | Hypersynchronized slow wave activity | Thalamus | Physical repair (growth hormone) | 15–20% |
| REM | Low-amplitude, mixed frequency | Sawtooth waves, atonia, sharply peaked eye movements | PPT/LDT | Memory consolidation | 20–25%** |
*
REM sleep is reduced in traumatic brain injury relative to matched controls.56
EEG, electroencephalogram; TST, total sleep time; REM, rapid eye movement; PPT, pedunculopontine tegmental nucleus of pans and midbrain; LDT, laterodorsal tegmental nucleus of pans and midbrain.