of different subcircuits, we can expect that, some of the issues will be clarified. Another important function of the BG is in the control of reward and reinforcement-based learning. This function overlaps to some extent with its role in movement control, as most learning and memory assays depend on performance of a particular set of movements. The NAc and downstream regions are implicated in responses to both rewarding and aversive stimuli, as well as in Pavlovian learning that involves conditioning stimuli to both appetitive and aversive unconditioned stimuli. These are brain areas high involved during the early stages of reward motivated learning and the response to substance of abuse. A NAc core and shell regions can be identified based on the inputs, projections patterns and immunochemistry markers, such as differential distribution of the calcium binding protein Calbindin D, as seen in rodents and humans (Groenewegen, Wright et al. 1999) (Voorn, Brady et al. 1994). The NAc core has multiple resembles with the dorsomedial striatum while the shell has more diverse features and can be further segregated into subregions (dorsomedial, intermediate, and ventrolateral) based on differences in gross projection patterns (Heimer, Alheid et al. 1997, Usuda, Tanaka et al. 1998) and
