Alcohol-induced impulsivity in rats : an effect of cue salience?

There is a common assumption that alcohol produces impulsive behaviors, thereby increasing the preference for immediate over delayed rewards. An alternative explanation, provided by alcohol myopia theory, is that alcohol alters attentional processes such that intoxicated individuals respond exclusively to the most salient cues in their environment. We tested these two hypotheses in rats using standard (impulsivity) and modified (cue salience) versions of the delayed reinforcement task. In the impulsivity paradigm, rats were trained to choose between a small immediate reward (2 sucrose pellets) and a large delayed reward (12 sucrose pellets after 10 s) in a T-maze. In the cue salience paradigm, a light in one arm predicted either the small or the large reward, but the arm paired with the light varied across trials. In separate experiments, we examined how changes in delay to the large reward, alcohol administration, or alcohol combined with either a serotonin agonist [para-chloroamphetamine (pCA) at doses of 0.1, 0.4, 0.7, and 1.0 mg/kg, s.c.)] or a dopamine antagonist [cis-(Z)-flupenthixol dihydrochloride (alpha-flupenthixol) at doses of 0.0125, 0.025, 0.05, and 0.1 mg/kg, i.p.] affected performance in each task. Increasing the delay to the large reward increased impulsivity in both paradigms, but it had no effect on responding to a salient cue. Alcohol (0.6, 0.9, 1.2, and 1.8 g/kg, i.p.) increased the choice of the immediate reward and increased the choice of the lit arm, regardless of whether it signaled the small or the large reward. pCA selectively reduced alcohol-induced impulsivity, whereas alpha-flupenthixol selectively reduced responding to a salient cue. Rats, like humans, are influenced by cue salience when intoxicated. Although this alcohol myopia effect could explain alcohol-induced impulsivity, the two processes are probably distinct because they are mediated by dissociable pharmacological mechanisms.