Increased activity in the during rem sleep may best explain why dream images are often accompanied by a strong emotional tone.

The limbic system is most likely responsible for emotional responses in REM sleep. Within this system are the amygdala, hipocampus, thalamus, hypothalamus, basal ganglia, and cingulate gyrus. Respectively, these are responsible for such reactions as: emotional response, the memory center, learning, changes in emotional reactivity, physical movements, and smells, sights, reactions to pleasant memories, reactions to emotional pain, and regulation of behavior.

It allows water to resist freezing and thawing cycle.