Neuronal cell firing was classified into one of four types of discharges within previously defined epochs relative to the reinforced response (Carelli, 2000). Briefly, neurons were classified as type pre-response (PR) if significant increases in cell firing were observed within a 1 s window of the 2.5 s pre response epoch. Type reinforcement-excitation (RFe) or reinforcement-inhibition (RFi) neurons exhibited significant increases or decreases, respectively, in firing that occurred within a 1 s window within the 2.5 s epoch immediately after response completion. Nonphasic (NP) cells showed no change in cell firing relative to baseline to the reinforced response for cocaine. The 1 s ‘sliding’ window of peak/trough changes in cell firing within the 2.5 s epochs were used since there is variability in the precise timing of neural changes across cells relative to the response, described previously (Carelli, 2000). Classification of each cell type into type PR, type RFe, type RFi or type NP cells was determined with z-score statistics for each neuron (p < 0.05). Z-scores were calculated as (x + b)/s, where x is the mean firing rate
