Sagittal rodent brain section illustrating the afferents and efferents of the lateral habenula (LHb). The LHb interconnects the forebrain with the midbrain and hindbrain regions by receiving afferents through the stria medullaris (SM), which contains fibers from the hippocampus (HIP), ventral pallidum (VP), lateral hypothalamus (LH), entopeduncular nucleus (EPN; the EPN is equivalent to the globus pallidus interna in primates and humans and sends a prominent afferent to the LHb (Hong and Hikosaka, 2008; Wallace et al., 2017)) diagonal band of Broca (cholinergic nerve fibers, not shown), lateral septum (LS), lateral preoptic area (LPO), ventral tegmental area (VTA; Stamatakis et al., 2013; Lammel et al., 2015), nucleus accumbens (NAc), anterior cingulate cortex (ACC) and the anterior insula (INS; afferent brain regions labeled in gray). The LHb then relays information via glutamatergic efferents that together form the fasciculus retroflexus. These efferents project to the substantia nigra (SNr), VTA, rostral medial tegmental nucleus (RMTg), the dorsal raphe nuclei (DRN), the locus coeruleus (LC) and the periaqueductal gray (PAG) (LHb-projecting brain regions labeled in black; Aizawa et al., 2011; Shelton et al., 2012; Quina et al., 2015; Yetnikoff et al., 2015).