This 2013 human study provided more details about dream sleep. The thalamus portion of the limbic system coordinates REM stages, which play critical roles in learning and memory.

This study also noted that science assigns no functions to dreams themselves, which was the first I’d heard of it.

http://www.pnas.org/content/110/25/10300.full “Rhythmic alternating patterns of brain activity distinguish rapid eye movement sleep from other states of consciousness”