Spontaneous recovery and dishabituation of ethanol-reinforced responding in alcohol-preferring rats

This study examined whether habituation, a decrease in responsiveness to a repeatedly presented stimulus, occurs to ethanol reinforcers in alcohol-preferring (P) rats. Three fundamental properties of habituation were evaluated: generality, spontaneous recovery, and dishabituation. In each experiment, P rats' lever pressing was reinforced by 10% ethanol on a variable-interval 15-s schedule during 50-min sessions. Experiment 1 evaluated the generality of habituation to repeatedly presented stimuli by using ethanol and water reinforcers. Rates of responding were higher for ethanol than they were for water. Additionally, the within-session patterns of responding differed for each reinforcer, suggesting that the pattern of responding was specific to the exact nature of the repeatedly presented reinforcer. Experiment 2 examined spontaneous recovery, an increase in responsiveness to a habituated stimulus when that stimulus is not presented for a time, by separating experimental sessions by 5 min, 2 hr, or 24 hr. Early-session rates of responding during Session 2 were slower than the corresponding rates during Session 1 when sessions were separated by 5 min or 2 hr. Response rates and within-session patterns of responding during Sessions 1 and 2 were similar when sessions were separated by 24 hr. Experiment 3 tested for dishabituation, a restoration of responsiveness following the presentation of an extraneous stimulus, by presenting a tone or a light 24 min and 55 s into the session. Rates of responding temporarily increased after the tone was presented. The results of these experiments support the idea that habituation contributes to the regulation of ethanol consumption.