Fig. 1.

Different categories of neuronal responses in mPFC and NAc during cocaine and heroin self-administration.A, Raster and perievent histogram plots show excitatory anticipatory and post-cocaine inhibitory responses by a mPFC neuron. Each dot in the raster plot (top) represents a neuronal spike, and each row represents an individual trial. The perievent histogram (bottom) depicts the average neuronal activity of the individual trials within the raster around the lever press event (50 sec before and 100 sec after lever press in this case). The zero point corresponds to the behavioral event of the lever press for cocaine self-administration. An increase in spike activity was found a few seconds before the lever press (excitatory anticipatory response), and a decrease in neuronal activity was observed after cocaine self-infusion (post-cocaine inhibitory response). B, Example of an excitatory anticipatory response during a heroin self-administration session by a NAc neuron. C, Inhibitory anticipatory neuronal response recorded from the mPFC during cocaine self-administration. Note a decrease in firing rate before the lever press. D, Excitatory post-heroin response recorded from a mPFC neuron during a heroin self-administration session. An increase in spike activity after heroin infusion is evident.