The relationship between each length of REM - NREM sleep cycle and sleep stage

A series of non rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep (REM-NREM sleep cycle) repeats across night. The length of REM-NREM sleep cycle varies between nights or individuals. However, the cause of the variation, which may represent characteristics of sleep, has not been well understood. To verify the cause of the variation, the relationship between each length of REM-NREM sleep cycle and included sleep stage was analyzed. We used the obtained data which consisted of 143 days with 6 to 7-hour sleep (37 healthy males in their 20s). The variation in each length of REM-NREM sleep cycle (Cycle No.1-4 in order of appearance) were observed. Each length of Cycle No.1-4 had positive correlations with stage 1+2 and stage REM. Therefore, each length of REM-NREM sleep cycle represented characteristics of each phase of sleep and could be useful to evaluate sleep quality.