AP PSYCHOLOGY

Detailed explanation-1: -This drowsy period, called stage I sleep, eventually gives way to light or stage II sleep, which is characterized by a further decrease in the frequency of the EEG waves and an increase in their amplitude, together with intermittent high-frequency spike clusters called sleep spindles.

Detailed explanation-2: -Along with another wave pattern called K-complexes, sleep spindles are considered a hallmark of stage 2 NREM sleep.

Detailed explanation-3: -They manifest as soon as we leave the transitionary state of sleep onset and enter the light phases of NREM sleep. From then on, they are generated regularly about every 3 to 6 seconds. Spindles occur during both light NREM sleep and deep slow-wave sleep, but not during REM sleep.

Detailed explanation-4: -As we move into stage 2 sleep, the body goes into a state of deep relaxation. Theta waves still dominate the activity of the brain, but they are interrupted by brief bursts of activity known as sleep spindles (Figure SC. 9).

Detailed explanation-5: -Stage II is the predominant sleep stage during a normal night’s sleep. The distinct and principal EEG criterion to establish stage II sleep is the appearance of sleep spindles or K complexes. The presence of sleep spindles is necessary and sufficient to define stage II sleep.