The striatum is a heterogeneous structure, with distinct anatomical and functional subterritories that can be broadly classified into the dorsal and ventral striatum. The majority (>90%) of the neurons in the striatum are GABAergic medium spiny neurons (MSN) with most (~80%) of the synapses being asymmetric glutamatergic inputs (Wilson, 2007; Tepper et al., 2008). In addition, there are at least three other types of interneurons, including a small population of cholinergic interneurons (~2%) that provide a rather extensive arborization in this region to modulate DA release probability (Zhou et al., 2002; Pakhotin and Bracci, 2007). The dopaminergic neurons arising from the VTA project to the ventral striatum (NAc and part of the olfactory tubercle), while the dorsal striatum (caudate-putamen) receives dopaminergic inputs primarily from the substantia niagra pars compacta. The ventral striatum is highly involved in the reinforcing effects of drugs of abuse and receives extensive excitatory afferents from the PFC, amygdala and hippocampus (Carelli, 2002; Volkow et al., 2006). On the other hand, efferent projections from the motor cortex to the dorsal striatum allows this subregion to gate sensorimotor
