A total of 75 NAc neurons (34 cells in the core; 41 neurons in the shell) were recorded in combination with voltammetric measurements of phasic dopamine release. Across all neurons, the average baseline firing rates was 2.5 ± 0.3 Hz. Of the 75 NAc cells, 29 neurons (39%) exhibited one of three types of patterned discharges within seconds of the reinforced response for cocaine similar to that previously described (Carelli, 2000). Figure 3 shows an example of a single NAc neuron recorded in the shell that exhibited patterned cell firing and phasic dopamine release relative to the cocaine-reinforced response across a single self-administration session. As seen in the color plot averaged across all self-administration trials (Figure 3, top), the cyclic voltammetric data shows an increase in [DA] that reached a maximum concentration of 130 nM immediately before the response, with a second increase in dopamine (maximum of 157 nM) approximately 4 s following the lever press response. The [DA] increase relative to the lever press was confirmed with principal component regression (Figure 3 bottom, blue trace superimposed on the peri-event
