Figure 2.

Neural circuits involved in circadian and metabolic regulation of arousal and sleep. The SCN (a master oscillator, red outline) is phase set by external timing cues, primarily light/dark signals, and directly connects to hypothalamic feeding centres the Arc and DMH (robust semi-autonomous oscillators, dark red outline) via primarily GABAergic connections to inhibit arousal during the day. The DMH and LH integrate peripheral metabolic signals to either inhibit sleep promoting regions in the POA or activate arousal and food seeking behaviours. The SCN also directly interacts with the PVT, an area also heavily implicated in modulating arousal response to metabolic need. ARC = arcuate nucleus, DMH = dorsomedial hypothalamus, LH = lateral hypothalamus, POA = preoptic nucleus, PVT = paraventricular thalamus, SCN = suprachiasmatic nuclei, TMN = tuberomamillary nucleus.