Afferent pathways to hypothalamic nuclei arise primarily from the brainstem, thalamus, basal ganglia, cerebral cortex, and olfactory areas. The detailed anatomy of these connections and hypothalamic interconnections is described in several fine reviews.1,3,4 Briefly, the reticular formation and visceral centers of the brainstem connect with the hypothalamus through two prominent pathways, the mammillary peduncle and the dorsal longitudinal fasciculus. Visceral and somatic information also reaches the hypothalamus from the locus ceruleus, vagal nuclei, periaqueductal gray area, and nuclei of the solitary tract (Fig. 8-5). The fornix transmits fibers from the hippocampus by direct projections to the mammillary bodies. Additional afferents from the piriform cortex and the amygdala also reach the hypothalamus, probably by other routes. Olfactory information through the medial forebrain bundle and stria terminalis reaches the hypothalamus either directly or indirectly through the previously mentioned cortical regions, the stria terminalis being the primary pathway from the amygdala. Most of the afferent pathways are reciprocal; thus, the hypothalamic efferent connections are extensive.