“…Several internal physiological signals emerging from the body's arousal/wakefulness and homeostatic brain circuits feedback to influence circadian timing in the SCN [ (Mrosovsky, 1996;Hut & Van der Zee, 2011;Hughes & Piggins, 2012;Belle, 2015;Meijer & Michel, 2015); see next section below]. These non-photic inputs include neuropeptide Y (NPY) neurons of the thalamic intergeniculate leaflet (IGL) which send axonal projections through the geniculo-hypothalamic tract (GHT), the serotonergic system of the raphe nuclei (Harrington, 1997;Morin, 2013), the basal forebrain cholinergic system (Bina et al, 1993;Yamakawa et al, 2016), as well as the arousal-promoting orexinergic neurons of the lateral hypothalamus (Mieda & Sakurai, 2012) which projects in the vicinity of SCN neurons (Date et al, 1999;Belle et al, 2014). In nocturnal rodents, a dark-pulse during the daytime causes increased locomotor activity together with a reduction of c-fos expression in the SCN (Marston et al, 2008).…”