(A) The human basal forebrain depicted in a series of coronal sections through the right hemisphere from the level of the ventral striatum (1) to the level of the caudal amygdala (4). The central extended amygdala is depicted in yellow, the medial extended amygdala in green. The images were modified (with permission) from , Art by Medical Scientific Illustration, Crozet, Virginia. See original reference for details. (B) Schematic pseudo-3D illustration of the right amygdala within the medial temporal lobe (modified with permission). For continuity, the central extended amygdala is depicted in yellow, the medial extended amygdala in green. The extended amygdala is depicted as a continuous bridge of neurons running from the Ce and Me, through the SI region, to the BST and the VS (shell of the nucleus accumbens). (C) 3D rendering of the rhesus monkey brain showing the approximate location and angle of the enlarged photo on the right. The autoradiograph (dark-field illumination) depicts axon transport in the rhesus monkey following an injection of ³H-amino acids into the region of the Ce. Note the dense labeling of axons and terminals through the sublenticular area of the extended amygdala (reprinted with permission). Abbreviations: ac: anterior commissure; BLA: basolateral complex; BSTL: lateral bed nucleus of stria terminalis; BSTM: medial bed nucleus of stria terminalis; BSTS/st: bed nucleus of stria terminialis, supra-capsular part/stria terminalis; Ce: central nucleus of the amygdala; f: fornix; ic: internal capsule; LV: lateral ventricle; Me: medial nucleus of the amygdala; opt: optic tract; ox: optic chiasm; SI; substantia innominata; SLEA: sublenticular part of extended amygdala; VS: ventral striatum.

(A) In vivo PET image demonstrating 5-HTT binding availability in the Ce and dorsomedially adjacent substantia innominata (SI) region, adapted from data first reported in . The image is thresholded at 250X the background binding level, and the circles indicate the regions of interest (ROIs) used in the present study as seed clusters for analysis of the monkey functional connectivity data. (B) Comparable low-power photomicrograph showing the dense and selective expression of 5-HTT in the lateral division of the Ce (image provided by Dr. Julie Fudge, University of Rochester School of Medicine and reprinted with permission of the publisher).

(A) Monkey and (C) human brain regions where the fMRI time-series were highly correlated (monkey: dark purple: t = 10.0; dark green: t = 20; light green: t = 30; human: dark purple: t = 16.0; dark green: t = 20; light green: t = 24). The Ce seed region is depicted in the adjacent section for both monkey and human (light purple). Red with yellow outline represents the 95% spatial confidence intervals around the peaks of the Ce-correlated activity within each cluster. Sections modified (and reprinted with permission) from stereotaxic atlases of the (B) rhesus monkey brain () and (D) human brain () corresponding to the MRI slices shown in A and C, respectively. The BST is depicted in light blue.