The cortical components of the associative circuit consist of areas that process sensory, motor and cognitive information at a stage with greater integration than primary sensory or motor cortices (Yin and Knowlton 2006). Examples include parts of the temporal and posterior parietal cortex, as well as prefrontal cortical regions. These cortical regions project predominantly to more medial areas of dorsal striatum (dorsomedial striatum, DMS) in the rodent brain (roughly equivalent to the primate caudate nucleus). Several anterior and medial and lateral thalamic regions project to DMS, and medial portions of the substantia nigra pars compacta (SNc) provide the bulk of dopaminergic innervation of this striatal subregion. The DMS MSNs project to the more medial parts of the GPe, GPi and SNr, and the GPe interacts with subregions of the STN. Ultimately, this circuit loop influences output from the same associative cortical areas that feed into the DMS (Balleine, Delgado et al. 2007) (Belin, Jonkman et al. 2009), although there is potential for cross-talk between circuits at several levels, which will be discussed later in this review.
