Glossary of Sleep-related terms

Sleep Stage 1 (NREM Stage 1)

A stage of NREM sleep that ensues directly from the awake state. Its criteria consist of a low-voltage EEG tracing with well defined alpha activity and theta frequencies in the 3 to 7 cps range, occasional vertex spikes, and slow rolling eye movements (SEMs), and includes the absence of sleep spindles, K complexes, and REMS. Stage 1 normally represents 4-5% of total sleep.1