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 areas activated during REM sleep are approximately inverse to those activated during non-REM sleep and display greater activity than in quiet waking. The "anterior paralimbic REM activation area" (APRA) includes areas linked with emotion, memory, fear and sex, and may thus relate to the experience of dreaming during REMS. More recent PET research has indicated that the distribution of brain activity during REM sleep varies in correspondence with the type of activity seen in the prior period of wakefulness. The superior frontal gyrus, medial frontal areas, intraparietal sulcus, and superior parietal cortex, areas involved in sophisticated mental activity, show equal