Figure 1.

Nucleus accumbens localization and connections. (a) Coronal cross-section through the human brain at the level of nucleus accumbens (NAc) occupying the lowest part of striatum, poorly separated from the other areas and divided into a centrally localized core (NAcc) and a peripherally situated shell (NAcs). Medially and upwards, it changes into the caudate nucleus (CDn), and laterally into the putamen (Put). Whereas the dorsal part of the striatum belongs to the locomotor system, its ventral part is considered as a structure of the limbic system. Fibers of the internal capsule (IC) surround NAc superiorly. The localization of NAc on the border of motor and limbic structures enables its integrative and coordinating function upon both systems. (b) Due to its localization in the center of the hemisphere, NAc can develop extensive connections with numerous brain areas that can be divided into structural and functional levels (i.e., cortical structures, hemispheric subcortical structures, diencephalic structures, and brain stem structures). This hierarchical arrangement reflects not only the consecutive stages of phylogenetic brain development but also the pattern of cooperation among several functional systems representing various levels of integration.