Figure 1.

Diagram illustrating select connectivity of brain structures involved in the voluntary control of rodent behavior. Four regions of rodent striatum are indicated by labels and color; the color gradient approximates the gradient of afferent projections (Voorn et al., 2004). Corresponding color in the other structures represents general projection topography. Note that ventral hippocampus has direct projections outside of the hippocampal formation, whereas the dorsal hippocampus does not (see text). Tapered arrows indicate highly convergent input. Output of the striatum can proceed through two distinct pathways to reach the thalamus and other targets: a “direct” pathway that has a disinhibitory effect (+), and an indirect pathway that has an inhibitory effect (−). These pathways are innervated by separate populations of medium spiny neurons in the striatum that predominantly express D1 (direct) or D2 (indirect) dopamine receptors. Projections from dopamine neurons in the VTA and SNc are shown in red. The overarching organization is that of loops linking neocortex, basal ganglia, and thalamus. The table indicates some characteristic features of dissociated behavioral control systems, with color indicating corresponding brain structures. Abbreviations for the table: stimulus (S), context (C), affective outcome (Oa), response (R), specific outcome (O). Abbreviations for the main figure: DLS, dorsolateral striatum; DMS, dorsomedial striatum; VSc, core of the nucleus accumbens in ventral striatum; VSs, shell of the nucleus accumbens in ventral striatum; VTA, ventral tegmental area; SNc, substantia nigra pars compacta, SNr, substantia nigra pars reticulata, P, pallidum; STN, subthalamic nucleus; dH, dorsal hippocampus; vH, ventral hippocampus; ENT, entorhinal cortex; BLA, basolateral nucleus of the amygdala; CN, central nucleus of the amygdala. The following regions of neocortex are labeled: IL, infralimbic; PL, prelimbic; OF, orbitofrontal; CG, cingulate, PP, parietal; SMA, sensorimotor.