Changes over the night in REM-sleep microstructure. A hypothesis of similarity to changes in dream features reported in the literature

The research aimed at a quantitative description of the changes in REM-sleep microstructure throughout the night. For this purpose, sleep recordings available on the public "PhysioNet" website were analyzed from a chronobiological perspective. This approach was suggested by the fact that two important properties of REM sleep determine its microstructure: the alternation between phasic and tonic microstates, and the presence of Slow Eye Movements in addition to Rapid Eye Movements. Although the examined recordings did not include data about dreams, a significant result of our analyses was the close similarity between the observed highly statistically significant changes in the microstructure and changes in basic dream features that are amply reported in the literature, including recall, word count, vividness and emotional content.