Stage

Occasionally a patient may go on to Stage III sleep. In this phase, there are still vertex waves, spindles, and K-complexes, but they occur less frequently and seem to be overwhelmed by the more prominent delta wave activity (<4 Hz). This slow wave activity is widespread but has a frontal and central predominance. It should be the most frequently noted rhythm and should be present for 20 to 50% of the record (Fig. 6). Stage III and the later Stage IV of sleep are most often associated with increases in the interictal discharges of temporal lobe epilepsy.

Fig. 6. As a subject progresses into Stage III sleep, as shown here, the background slows into the delta frequency range and is present approx 40% of the time.
Fig. 7. When the background is more than 50% delta activity, the subject is considered to be in Stage IV of sleep, as noted on this portion of the record.

Fig. 8. Rapid eye movement sleep follows Stage IV in the sequencing of sleep. As noted here, the background is a low-voltage fast rhythm, as is seen in the wakeful state, but is also associated with lateral eye movements with a frequency of approx 1 Hz. These eye movements are seen over the lateral temporal leads, where they are out of phase with each other from side to side.

Fig. 8. Rapid eye movement sleep follows Stage IV in the sequencing of sleep. As noted here, the background is a low-voltage fast rhythm, as is seen in the wakeful state, but is also associated with lateral eye movements with a frequency of approx 1 Hz. These eye movements are seen over the lateral temporal leads, where they are out of phase with each other from side to side.

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