Other groups, following Pavlovian and instrumental conditioning, were subsequently trained to self-administer cocaine with nosepoke responses, or received yoked saline infusions and nosepoked for water rewards, and then performed PIT while electrophysiological recordings were taken in the nucleus accumbens. Behaviorally, although both naive and saline-treated groups showed increases in lever pressing during the conditioned stimulus cue, this effect was significantly enhanced in the cocaine-treated group. Neurons in the
core and shell tracked these behavioral changes. In control animals, core neurons were significantly more likely to encode general information about cues, rewards and responses than those in
the shell, and positively correlated with behavioral PIT performance, whereas PIT-specific encoding in the selleck products shell, but not core, tracked PIT performance. In contrast, following cocaine exposure, there was a significant increase in neural encoding of all task-relevant events that was selective to the shell. Given that cocaine exposure enhanced both behavior and shell-specific task encoding, these findings suggest that, whereas the core is important for acquiring the information about cues and response contingencies, the shell is important for using this information to guide and modulate behavior and is specifically affected following a history of cocaine check details self-administration. Animals are faced with the necessity of seeking rewards in their environments. Whereas natural rewards
such as food or mates motivate much goal-directed behavior, similar mechanisms appear to drive seeking for drugs of abuse such as cocaine (Parkinson et al., 2000a; Everitt et al., 2001; Robbins & Everitt, 2002). Further, through associations with Baf-A1 mouse the reward, environmental cues acquire motivational significance that can influence goal-directed behavior (Holland & Rescorla, 1975; Hyde, 1976; Rescorla, 1994; Arroyo et al., 1998). For example, food-related cues can induce feeding in rats that are completely sated, suggesting that such motivational cues have the ability to over-ride homeostatic satiety signals (Holland & Petrovich, 2005). Similarly, animal and humans will re-engage in drug-taking behaviors when presented with drug-associated cues after long periods of abstinence (Grimm et al., 2002; Kalivas & McFarland, 2003; Fuchs et al., 2004). These findings argue that Pavlovian cues provide powerful motivational features through their associations with various reinforcers. Given these common associative mechanisms, understanding the manner in which learning comes to guide goal-directed behavior for natural rewards can also provide insight into similar processes that become pathological in the drug-addicted state.