PS onset and maintenance is due to the inhibition of these PS-off neurons by PS-on GABAergic neurons localized in the posterior hypothalamus, the ventrolateral periaqueductal gray, and the lateral and dorsal paragigantocellular reticular nuclei. The SLD neurons are inactivated during waking and slow-wave sleep by PS-off GABAergic neurons localized in the ventrolateral periaqueductal gray and the adjacent deep mesencephalic reticular nucleus. We propose that muscle atony during PS is due to the activation of PS-on glutamatergic neurons localized in the caudal pontine sublaterodorsal tegmental nucleus (SLD) and the glycinergic/GABAergic premotoneurons localized in the medullary ventral reticular nuclei. In the present review, we present the most recent results on the neuronal network responsible for PS generation. Rapid eye movement sleep (REM or paradoxical sleep (PS)) is a state of sleep characterized by REMs, EEG activation, and muscle atony. Patrice Fort, in Handbook of Behavioral Neuroscience, 2019 Abstract Disinhibition of GABAergic neurons in the pons may also be involved in REM-sleep generation. Orexin/hypocretin neurons also regulate REM-sleep timing via activation of the LC. In addition stimulation of serotonergic, noradrenergic, or histaminergic cells will inhibit REM sleep. Reciprocal inhibitory interactions between the REM-ON and REM-OFF neurons are thought to be involved in REM-sleep regulation. REM-ON neurons inhibit REM-OFF neurons and thus promote REM sleep. GABAergic REM-ON neurons are located in the sublaterodorsal nucleus/peri-LC and the periventricular gray matter, and GABAergic REM-OFF neurons are located in the ventrolateral part of the periaqueductal grey matter and the lateral pontine tegmentum. However, there are special populations referred to as REM-ON neurons that fire only during REM sleep, REM-OFF neurons that fire during wakefulness and are off during REM sleep, and a population of cholinergic neurons that fire during both REM sleep and wakefulness. REMs and other phasic activity such as middle ear muscle activity may be present during REM sleep.Ĭholinergic neurons in the reticular formation are active during REM sleep, primarily those located in the pontine tegmentum. However, skeletal muscle activity is actively inhibited during REM sleep. Respiration, heart rate, and brain glucose utilization are more variable and activity can be as high as that observed during wakefulness. Compared to NREM sleep, REM sleep is considered the sleep state with the highest physiological arousal. REM sleep is also characterized by the presence of pontine–geniculate–occipital (PGO) waves as well as hippocampal theta EEG activity. REM sleep is defined by low-amplitude desynchronized theta EEG activity with the presence of saw-tooth waves at the cortex. Wright, in Encyclopedia of Behavioral Neuroscience, 2010 REM sleep
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