Neural integrative activities of nucleus accumbens subregions in relation to learning and motivation

In recent years, there has been much interest in the functional specializat ions of nucleus accumbens subregions. The two zones within the nucleus accu mbens that have received considerable attention are the accumbens core, con sisting of ventral striatal tissue surrounding the anterior commissure, and the accumbens shell, which envelops the core on its medial, ventral, and l ateral borders. Differential connectivity and histochemical profiles sugges t that these two subterritories may have distinctive behavioral roles with regard to the regulation of motivated behavior. Experiments focusing primar ily on amino acid-coded neurotransmitter systems in these regions-that is, glutamate and gamma-amino butyric acid (GABA)-have revealed specific and co ntrasting functions of the core and the shell. It is proposed that the accu mbens core, and specifically N-methyl-D-aspartate receptor-dependent plasti city within this area, is part of a network critical for appetitive instrum ental learning, in which a motor response becomes "stamped in" when followe d by a rewarding stimulus or event. The accumbens shell, particularly GABA and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors with in the shell, is implicated in the executive control of brain feeding circu its and may also represent a key area at which appetitive and aversive stim uli interact to control behavioral selection. These functional specializati ons within the nucleus accumbens subregions may be Integrated through the c oordination of activity within striatal neuronal ensembles that communicate with complex networks of limbic, thalamic, and prefrontal circuitry.