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 phase. The prospect that well-known neurological aspects of REM do not themselves cause dreaming suggests the need to re-examine the neurobiology of dreaming "per se". Some researchers (Dement, Hobson, Jouvet, for example) tend to resist the idea of disconnecting dreaming from REM sleep. After waking from REM sleep, the mind seems “hyperassociative”—more receptive to semantic priming effects. People awakened from REM have performed better on tasks like anagrams and creative problem solving. Sleep aids the process by which creativity forms associative elements into new combinations that are useful or meet some requirement. This occurs in REM sleep rather than in