Correlates of recovery from incentive downshift: A preliminary selective breeding study

Rats exposed to a downshift in the concentration of a sucrose solution from 32% to 4% exhibit a transient suppression of consummatory behavior relative to an unshifted control always exposed to 4% sucrose. One explanation of this effect, known as consummatory successive negative contrast (cSNC), explains consummatory suppression as arising from an emotional state of frustration that redirects behavior away from the source of the devalued solution. A preliminary selective breeding protocol consisting of three experiments was performed. Experiment 1 reports results from 5 generations of selected breeding for either high (H) or low (L) recovery rates from cSNC. A control line of randomly (R) mated rats was included. cSNC was reduced in H rats, but L and R rats did not differ across generations. H rats also provided no evidence of behavioral activation in acquisition or increased persistence in extinction after partial reinforcement, rather than continuous reinforcement. L and R rats, by contrast, showed both of these effects. H rats were also significantly smaller in body size than R rats, but did not differ in terms of water intake, sucrose sensitivity, open-field activity, or responding to sucrose solutions before the downshift. In Experiment 2, H infants from the sixth selected generation showed increased bandwidth in vocalizations induced by mother-infant separation relative to L and R rats. Experiment 3 showed that H rats failed to show increased response to incentive downshift after treatment with the nonselective opioid antagonist naloxone, as done by L and R rats. The results, if replicated, may provide support for the interpretation of a significant role of frustration in cSNC.