Fig. 3.

Comparison of mPFC neuronal activity during a cocaine-first, heroin-second self-administration session using the same plot as in Figure 2. A, This rate meter plot demonstrates the firing rate of a mPFC neuron during the entire cocaine–heroin self-administration session. In this case, heroin self-administration caused general inhibition. B, Raster and perievent histogram for cocaine self-administration trials. A decrease in firing rate occurred ∼2 sec before the lever press (inhibitory anticipatory response). C, Raster and perievent histogram for heroin self-administration trials. The inhibitory anticipatory response observed during cocaine self-administration trials (B) was absent during heroin selfadministration.