human biology - The fundamental importance of R.E.M. Sleep. (Rapid Eye Movement)

Question:

I know that experiments have been conducted to determine the importance of R.E.M. sleep in our sleep cycle. It is particularly important for learning, information synthesis, and recovery from distress. Why else is R.E.M. sleep important? What experiments have been done/observations been made to determine the neurological mechanisms underlying R.E.M. sleep? I know that we exhibit high frequency $\alpha$ waves, similar to the waves we experience during wakefulness.

Wiki:

During REM sleep, high levels of acetylcholine in the hippocampus suppress feedback from hippocampus to the neocortex, and lower levels of acetylcholine and norepinephrine in the neocortex encourage the spread of associational activity within neocortical areas without control from the hippocampus. This is in contrast to waking consciousness, where higher levels of norepinephrine and acetylcholine inhibit recurrent connections in the neocortex. REM sleep through this process adds creativity by allowing "neocortical structures to reorganise associative hierarchies, in which information from the hippocampus would be reinterpreted in relation to previous semantic representations or nodes.

Do these reorganized neocortical hierarchies remain this way?

Just HOW integral is R.E.M. sleep to our brain development?