Stage Ii

This stage's onset is identified by the appearance of spindles. They are frontal-centrally predominant waves that occur as a cluster lasting for one to several seconds in duration. The spindle frequency is between 11 and 15 Hz and, in healthy adults, they are bilateral and synchronous in their appearance, with an amplitude up to 30 |V. Spindles may appear by themselves or following a vertex wave. In that latter situation, the wave is called a "K complex" (Fig. 5). Vertex waves are increasingly prevalent in Stage II sleep, and often persist in deeper stages as well. During the progression into deeper aspects of Stage II, the background rhythm continues to slow into the slower theta ranges, and high voltage generalized and frontally predominant delta slow waves are noted (<4 Hz).

During Stage II of sleep, occipital predominant high-voltage sharp slow waves are occasionally noted. These waves look like the lambda waves described in Section 8. These are referred to as either lambdoid waves or posterior occipital sharp transients of sleep. The physiological basis for posterior occipital sharp transients of sleep is probably very similar to

Sleep Record Form

Fig. 4. Approximately half-way through this record, the alpha rhythm gradually fades and is replaced by slower theta frequency activity. There are no eye movement artifacts and this pattern evolved into Stage II sleep. Therefore, this tracing shows the transition from wakefulness to sleep, i.e., drowsiness.

Fig. 4. Approximately half-way through this record, the alpha rhythm gradually fades and is replaced by slower theta frequency activity. There are no eye movement artifacts and this pattern evolved into Stage II sleep. Therefore, this tracing shows the transition from wakefulness to sleep, i.e., drowsiness.

Sleep Record Form

Fig. 5. This record, approximately half-way through, shows classic frontal-centrally predominant fast bursts of "spindle" activity followed by a centrally predominant high-voltage slow sharp wave, vertex wave. This complex is also referred to as a "K-complex," and is one of the hallmarks of Stage II sleep.

Fig. 5. This record, approximately half-way through, shows classic frontal-centrally predominant fast bursts of "spindle" activity followed by a centrally predominant high-voltage slow sharp wave, vertex wave. This complex is also referred to as a "K-complex," and is one of the hallmarks of Stage II sleep.

lambda waves. Their relation to visual dreams remains contested. Occasionally, these waves may extend into Stage III of sleep.

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