Early-night serial awakenings as a new paradigm for studies on NREM dreaming.

A new experimental paradigm called "Early-Night Serial Awakenings" (ENSA) was explored to find out its strengths and weaknesses for psychophysiological studies of NREM sleep dreaming. Five participants spent 20 experimental nights in the sleep laboratory, and were serially awakened with approximately 24-minute intervals during Stages 2 and 3 of NREM sleep. As a total, 164 awakenings were conducted during the sessions that lasted on average 193 min. Altogether, 30% of NREM sleep awakenings led to dream reports, 39% to reports of white dreaming, and 31% to reports of dreamless sleep. Results also show that sleep EEG spectral power, dream recall frequency as well as dream complexity remained stable throughout the serial awakening sessions. We conclude that, as ENSA dreams appeared to be static and very limited in content, the paradigm we identified could be used in future studies to reveal the psychophysiological mechanisms of relatively simple forms of early-night NREM sleep dreaming.