Electrophysiological recordings in behaving animals show that distinct populations of NAc neurons encode the important features of goal-directed behaviors. During cocaine self-administration, we have shown that a subset of NAc neurons exhibit changes (increases and/or decreases) in firing rate within seconds of lever pressing for intravenous drug. Some NAc neurons discharge seconds before the cocaine reinforced response and appear to encode ‘anticipation’ of impending drug reward. Other NAc cells exhibit changes in firing rate within seconds following response completion and are activated by stimuli paired with drug infusion. Similar types of neuronal firing patterns have been observed during behavioral responding for natural (e.g., food/water/sucrose) reward (Wheeler & Carelli, 2008) and intracranial self-stimulation (ICSS) (Cheer et al., 2007).
