Simplified diagram of connections between the master circadian clock and sleep-wake circuitry. Diagram is color-coded as follows: Red = SCN, Green = generally wake-promoting, Purple = generally sleep promoting, orange = both, blue = neutral/other role, dotted lines = sparse projections. Abbreviations: ipRGCs, intrinsically photosensitive retinal ganglion cells; RHT, retinohypothalamic tract; SCN, suprachiasmatic nucleus; ARC, arcuate nucleus of the hypothalamus; VLPO, ventrolateral preoptic nucleus; dSPZ, dorsal subparaventricular zone; vSPZ, ventral subparaventricular zone; DMH, dorsomedial hypothalamus; TMN, tuberomammillary nucleus; LH, lateral hypothalamus; PVN, paraventricular nucleus; IGL, intergeniculate leaflet; PAG, periaqueductal gray; LC, locus coeruleus; SCG; spinal cervical ganglion.