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,
Non-rapid eye movement sleep several experiments that low levels of stage 3 sleep are observed in about 40-50% of people with acute and chronic schizophrenia (who typically experience abnormal non-rapid eye movement sleep). NREM sleep was divided into four stages in the Rechtschaffen and Kales (R&K) standardization of 1968. That has been reduced to three in the 2007 update by The American Academy of Sleep Medicine (AASM). Sleep spindles are unique to NREM sleep. The most spindle activity occurs at the beginning and the end of NREM. Sleep spindles involve activation in the brain in the areas of the thalamus, anterior cingulate and insular