Figure 11.

Effects of PAG opiate antagonist on blocking and extinction. The circuit that controls the activity of globally distributing reinforcement R and extinction X neurons (from Figure 5) is shown above. (A) Blocking. Each graph shows two reinforced co-occurrences of CS1 and CS2 in context A followed by test presentations of CS2 in context B. Details of first reinforced co-presentation of CSs are shown in the blow-ups. (A₁) Control; no prior experience. (A₂) CS1 was previously conditioned in context C. Note that the response to CS2 is less than in A₁ because the well-conditioned CS1 partially blocked learning. (A₃) Same as A₁ except that opiate receptors were 70% blocked during training (simulated by attenuating input from O-cells input to their targets) during the two conditioning trials. Magenta arrows mark initial test responses. (B) Effect of PAG opiate receptor block on extinction. (B₁) Normal conditioning and extinction. (B₂) Same as B₁ except opiate receptors partially blocked during exctinction.