Figure 6.

Striatal-domain substrates of model-free and model-based controllers. The proposed organization of navigation strategies and potential control of learning across the three striatal domains. The identification of the shell and core as “critics” for the model-based and model-free controllers in dorsal striatum partly rests on the “spiral” of striatal-dopamine-striatal projections (Maurin et al., 1999; Haber et al., 2000; Haber, 2003), originating in the shell of the VS (the spiral is indicated by the thicker lines) and on the permissive role dopamine plays in plasticity at cortico-striatal synapses (Reynolds et al., 2001; Shen et al., 2008). There are also closed loop links between dopamine cell populations and each striatal region. Abbreviations: Mb, model-based; Mf, model-free; PPn, pedunculopontine nucleus; SNc, substantia nigra pars compacta; VP, ventral pallidum; VTA, ventral tegmental area. Note that the “inhibitory” and “excitatory” labels refer to the dominant neurotransmitter of the connection, not the effect that connection may have on the target nucleus as a whole (e.g., basolateral amygdala input to VS neurons can suppress other excitatory inputs despite using glutamate, which is an “excitatory” neurotransmitter).