A 72-year-old woman with insomnia paicipates in a sleep study . As pa of the study protocol, she has EEG leads attached, then goes to sleep. At one point during the evening, 12-16 Hz sleep spindles and K-complexes are observed. Which of the following stages of sleep is associated with this pattern?

Stage 2 has more theta waves than stage 1 and is associated with sleep spindles (sho bursts of 12-16 Hz activity) and K-complexes (high amplitude slow waves with superposed sleep spindles) on the electroencephalogram. Transient large amplitude potentials in the occipital areas (ponto-geniculo-occipital spikes) are associated with REM sleep. Stage 1 or drowsiness, is characterized by the attenuation of alpha rhythm (8-13 Hz) and the appearance of 4-7-Hz theta waves. Stages 3 and 4, or slow wave sleep, are characterized by high amplitude slow waves, especially in the delta (< 4 Hz) frequency range.