Figure 22. Overview of the major afferent pathways to the hypothalamus. (A) Schematic organization of medial forebrain bundle (MFB). Fibers afferent to the hypothalamus enter the lateral wall of the hypothalamus and are shown in different colors in relation to their anatomical source (amygdala, septal areas, olfactory areas, frontal neocortex). Reciprocal efferent connections from the hypothalamus to the same regions are shown by dotted black lines parallel to the colored lines. Pink fibers (and related reciprocal black dotted lines) indicate the amygdalofugal (and related amygdalopetal) components of the ansa peduncularis, entering the hypothalamus as a part of the medial forebrain bundle. The mammillary body and anterior column of the fornix are colored light blue and lie medial to the course of medial forebrain bundle. (B) Schematic organization of limbic afferents to the hypothalamus via the fornix (fx), stria terminalis (st), stria medullaris (sm), and olfactory tract. Axons enter the rostral portion of the hypothalamus before coursing throughout its entire extent. (C) Course of afferent fibers from the thalamus, subthalamus and zona incerta to the hypothalamus. Efferents from the hypothalamus coursing in the mammillo-subthalamic tract are also shown. On the right side of the image, a three-dimensional reconstruction shows the anatomical structures schematically depicted on the left side. aap = amygdalofugal and amygdalopetal components of the ansa peduncolaris; ac = anterior commissure; Ah = Ammon horn; al = ansa lenticularis; am = amygdala; ap = ansa peduncularis; ATn = anterior thalamic nucleus; cc = corpus callosum. CN = caudate nucleus; CS = corpus striatum; df = dentate fascia; fl = fasciculus lenticularis; fr = fasciculus retroflexus; ft = fasciculus thalamicus; fx = fornix; H1 = field H1 of Forel; H2 = field H2 of Forel; ha = habenula; hipp = hippocampus; HYP = hypothalamus; ic = internal capsule; iTp-ap = inferior thalamic peduncle of the ansa peduncularis; LTn = lateral thalamic nucleus; mb = mammillary body; MFB = medial forebrain bundle; mst = mammillo-subthalamic tract; MTn = medial thalamic nucleus; mtt = mammillo-thalamic tract; olf-a = olfactory area; olf-n = olfactory nerve; olf =olfactory tubercle; opt = optic tract; pir = piriform cortex; pvs = periventricular system; RF = reticular formation of the brainstem; sa = septal areas; SN = substantia nigra; Sub = subthalamus; zi = zona incerta; III = third ventricle. (From Toni R, Malaguti A, Benfenati F, Martini L: The human hypothalamus: a morphofunctional perspective. J Endocrinol Invest 27 (supp to n.6), 73-94, 2004.)