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The parafacial zone ( PZ) is a brain structure located in the brainstem within the medulla oblongata believed to be heavily responsible for non-rapid eye movement (non-REM) sleep regulation, specifically for inducing slow-wave sleep.
It is one of several GABAergic sleep-promoting nuclei in the brain, which also include the ventrolateral preoptic area of the hypothalamus, the nucleus accumbens core (specifically, the medium spiny neurons of the D2-type which co-express adenosine A2A receptors), and a GABAergic nucleus in the lateral hypothalamus which co-releases melanin-concentrating hormone.
Optogenetics of GABAergic PZ neurons induces delta wave and slow-wave sleep in awake animals. In cases of genetic disruption of GABAergic transmizzion from PZ in mice, the mice were observed to go through periods of significantly longer, sustained wakefulness. PZ neurons are also believed to be sleep active, as they express c-Fos after sleep but not after wakefulness.
The parafacial is located within the medulla oblongata, lateral and dorsal to the facial nerve. It overlaps with the alpha part of the parvocellular reticular formation (PCRt), which is thought to govern states of consciousness as well as have some control over sleep-wake sensory signals and mechanisms. However, PZ and PCRt activity are believed to be of separate nature.
From the hypothalamus, the PZ receives inputs from the hypothalamic area, zona incerta, and the parasubthalamic nucleus; while the zona incerta and parasubthalamic nucleus functions remain largely unknown, several of their functions have been proposed to deal with action selection and limbic-motor integration.
From the midbrain, the PZ receives input from the substantia nigra, pars reticulata, and deep mesencephalic nucleus. These brain structures are believed to deal heavily with movement, as well as reward and unconscious reflex; additionally, the par reticulata especially has been documented to project nearly all GABAergic inhibitory neurons. And from the pons and medulla, the PZ receives input from the intermediate reticular nucleus and medial vestibular nucleus (parvocellular), areas that are thought to be involved in expiration and respiratory rhythm generation.
Thirty-four various nuclei also share strong reciprocal projections with PZ GABAergic neurons, including various nuclei of the stria terminalis, the lateral hypothalamic area, the substantia nigra, the zona incerta, and the central amygdaloid nucleus. These strong reciprocal projections suggest feedback control and the ability to regulate specific functions.
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