Operant behavior during sessions of intravenous cocaine infusion is necessary and sufficient for phasic firing of single nucleus accumbens neurons.

The activity of individual accumbens neurons in rats was recorded in relation to intravenous cocaine infusions that were either response (i.e., lever press) contingent or response non-contingent. Neural firing was additionally recorded in relation to non-reinforced lever presses. Comparisons of firing under the three conditions showed that operant behavior was necessary and sufficient for preinfusion firing to occur. Surprisingly, the same was true, in many cases, for firing that occurred during the infusion. For other neurons, firing during the infusion was unrelated to operant behavior and possibly related to infusion stimuli. The relationship to operant behavior exhibited by the majority of NAcc neurons is consistent with previous studies that demonstrated a necessary relationship between NAcc neurons and cocaine reinforced operant behavior.