Figure 4.

This figure represents the basic assumption and implications behind the use of a D1 agonist to test the hypothesis that the BLA is where the hippocampal system (HS) and extrahippocampal system (EHS) compete for associative control over the fear system. The left side of the figure represents the basal state of plasticity potential in the amygdala under normal conditions (A), and when D1 agonists are injected into the amygdala (B). The right side of the figure represents the resulting change in the strength of contextual fear associated with these two states after conditioning. In the normal state, output from the hippocampal system (via ventral subiculum) is expected to dominate the competition for available plasticity product needed to support the learning, as represented by the relative size of the arrow in C. The increased plasticity potential resulting from the D1 agonist is predicted to be large enough to support associated control to both the hippocampal and extrahippocampal systems, as represented in D.