Several features of the VS stand out as particularly unique. Firstly, embedded within parts of the VS are the islands of Calleja or cell islands, identifiable in all mammalian species by their dense core of granule cells,56 the largest of which (Calleja magna) forms the medial border of the nucleus accumbens. Additional, albeit smaller, islands (referred to as interface islands, 57) are located in the basal forebrain in primates, including humans. The neurochemical features of these islands suggest that they may function as a type of “endocrine striatopallidal system”. 58 Of particular interest is the fact that the cells in the islands are thought to contain quiescent, immature cells that remain in the adult brain.59 In support of this idea, studies show that bcl2 protein—which, though abundant in fetal neurons, persists in limited regions of the adult primate brain—marks these islands.60,61 Secondly, a subterritory of the VS, the shell region, divides the VS into two parts, a medial/ventral shell region and a central core region.62 Experiments aimed at delineating the functional significance of these two regions have been instrumental in
