Of the 29 phasically active cells recorded in both the core and shell, three types of neuronal firing patterns were observed relative to the reinforced response for intravenous cocaine, as illustrated by the population PEHs in Figure 4. Average (and SEM) changes in [DA] corresponding to locations at which each type of patterned discharge was observed are illustrated in the blue traces superimposed above the PEHs (Figure 4A, B & C). A subset of NAc neurons (n = 14) displayed increases in cell firing (peak increase of 2.23 ± 0.07 Hz) within seconds preceding the reinforced response with an abrupt decline in cell firing at response completion, termed type pre-response (PR cells), shown in Figure 4A. At these locations, significant increases in dopamine were observed (F13, 247 = 2.9, p < 0.0001). That is, a slight but non-significant increase in dopamine was observed approximately 8 s before the lever press followed by a more pronounced and significant increase in [DA] (maximum increase of 48.0 ± 1.5 nM) immediately following response completion. Other NAc neurons (n = 6) exhibited significant increases
