AM-251 modulates fear extinction performance. a) CS-elicited freezing during the three sessions. The A_V_V and V_V_V groups displayed significant extinction during Test 2. Letters in parentheses indicate pharmacological treatment during Test 3 (see Table 1). Again, in the absence of AM-251 the A_A_V and V_A_V groups (see Table 1) showed extinction during Test 3, but freezing responses remained high for the A_A_A and V_A_A groups. Asterisks indicate significant differences within groups, (P < 0.05). b) Baseline freezing responses during three daily test sessions. In the absence of AM-251, the A_A_V, V_A_V and A_V_V groups exhibited significant extinction during Test 3. However, the continued presence of AM-251, the A_A_A and V_A_A groups, maintained high baseline freezing levels. Asterisks indicate significant differences within groups, (P < 0.05).