Effects of early life and current housing on sensitivity to reward loss in a successive negative contrast test in pigs

Animals in a negative affective state seem to be more sensitive to reward loss, i.e. an unexpected decrease in reward size. The aim of this study was to investigate whether early-life and current enriched vs. barren housing conditions affect the sensitivity to reward loss in pigs using a successive negative contrast test. Pigs (n = 64 from 32 pens) were housed in barren or enriched conditions from birth onwards, and at 7 weeks of age experienced either a switch in housing conditions (from barren to enriched or vice versa) or not. Allotting pigs to the different treatments was balanced for coping style (proactive vs. reactive). One pig per pen was trained to run for a large reward and one for a small reward. Reward loss was introduced for pigs receiving the large reward after 11 days (reward downshift), i.e. from then onwards, they received the small reward. Pigs housed in barren conditions throughout life generally had a lower probability and higher latency to get the reward than other pigs. Proactive pigs ran overall slower than reactive pigs. After the reward downshift, all pigs ran slower. Nevertheless, reward downshift increased the latency and reduced the probability to get to the reward, but only in pigs exposed to barren conditions in early life, which thus were more sensitive to reward loss than pigs from enriched early life housing. In conclusion, barren housed pigs seemed overall less motivated for the reward, and early life housing conditions had long-term effects on the sensitivity to reward loss.

Consummatory Successive Negative Contrast in Mongolian Gerbil (Meriones unguiculatus)

Successive Negative Contrast (SNC) is a phenomenon in which there is a sharp decrease in the rate of reinforced behavior immediately after a sudden reduction in quality or quantity of a habitual reinforcer. This phenomenon has become a solid experimental paradigm for the study of frustration in mammals but it has not been reported to date in the Mongolian gerbil (Meriones unguiculatus). This species is monogamous and biparental, and these differential characteristics make it interesting for comparative analysis. This work includes modifications to the SNC paradigm for this species, assessing its response to sudden changes in positive reinforcement and its differences by sex. In the first phase of the experiment, a multiple choice test was used to identify the preferred reinforcer for the species (sesame paste). After the selection of the primary incentive, the contrast procedure was carried out by presenting sesame paste in the pre-shift phase and LabDiet Laboratory Rodent Diet food during post-shift one. A repeated measures ANOVA of showed a significant reduction of consummatory behavior in the experimental group when compared with the control group. No differences were observed by sex. These data expand the possibility of using gerbils in the comparative study of the relationship between learning and emotion in mammals, both in behavioral and in neurobiological levels.