Non-rapid eye movement sleep activation occurs during NREM that is comparable to the type that occurs during REM. It is this sub-cortical activation that results in dreaming during the NREM stage during the morning hours. During non-REM sleep, the tonic drive to most respiratory muscles of the upper airway is inhibited. This has two consequences: However, because the diaphragm is largely driven by the autonomous system, it is relatively spared of non-REM inhibition. As such, the suction pressures it generates stay the same. This narrows the upper airway during sleep, increasing resistance and making airflow through the upper airway turbulent and noisy. For example,
Rapid eye movement sleep whilst weaker, transient, "noise" memory traces disintegrate. Memory consolidation during paradoxical sleep is specifically correlated with the periods of rapid eye movement, which do not occur continuously. One explanation for this correlation is that the PGO electrical waves, which precede the eye movements, also influence memory. REM sleep could provide a unique opportunity for “unlearning” to occur in the basic neural networks involved in homeostasis, which are protected from this “synaptic downscaling” effect during deep sleep. REM sleep prevails most after birth, and diminishes with age. According to the "ontogenetic hypothesis", REM (also known in neonates as "active sleep") aids