Visual discrimination of male and female faces by infant rhesus macaques.

Recent studies have revealed that human infants process female faces differently from male faces. To test whether a similar preference for female faces exists in other primates, we presented nursery-reared infant rhesus macaques with photographs of macaque faces and human faces. At <1 month old, infant macaques preferentially oriented towards female macaque faces when faces were presented upright. No preference for female human faces was found. At 9 months old, infants failed to show a visual preference for female macaque faces or female human faces, although they showed significantly more lipsmacking responses at female human faces. Compared to human infants, macaques appear to have stronger predispositions early in life but this preference may nonetheless be amendable to experience. Understanding how innate predispositions and the social rearing environment shape infants' understanding of faces remain important issues to be explored in order to understand facial processing abilities in humans and other primates.

Tufted capuchin monkeys (Cebus apella) spontaneously use visual but not acoustic information to find hidden food items.

Foraging choices in tufted capuchins monkeys are guided by perceptual, cognitive, and motivational factors, but little is known about how these factors might interact. The present study investigates how different types of sensory information affect capuchins' ability to locate hidden food. In two experiments, capuchins were presented with two cups, one baited and one empty. Monkeys were given visual, acoustic, or acoustic-visual information related to the baited cup, the empty cup, or both baited and empty cup. Results show that capuchins spontaneously used visual information to locate food, and that information indicating presence and absence of food led to higher success rates than information indicating only absence of food. In contrast, acoustic information did not lead to success rates above chance levels and failed to enhance performance in combination with visual information. Capuchins spontaneously avoided a visually empty cup, but they did not appear to associate sounds with either the presence or absence of food. Being able to locate food items with the aid of acoustic cues might be a learned process that requires interactive experiences with the task's contingencies.

The foraging ball as a quick and easy enrichment device for pigs (Sus scrofa).

Providing research pigs with enrichment objects can encourage species-typical behavior such as rooting and foraging. The authors gave pigs hard plastic 'foraging balls' that resembled enrichment devices commonly used for nonhuman primates. Holes were custom-drilled into the balls, and animal caretakers filled them with palatable food items such as jellybeans, unsalted peanuts, cereal, Beggin' Strips, primate biscuits and dog biscuits. Staff members suspended the balls from chains in pigs' enclosures, ensuring that toys did not touch the floor. All pigs manipulated the balls and were able to obtain treats that were supplemental to their standard diet. The simple and effective enrichment device was easily incorporated into the daily routines of research facilities, with little disruption to schedules.

On loss aversion in capuchin monkeys.

Chen, Lakshminarayanan, and Santos (2006) claim to show in three choice experiments that monkeys react rationally to price and wealth shocks, but, when faced with gambles, display hallmark, human-like biases that include loss aversion. We present three experiments with monkeys and humans consistent with a reinterpretation of their data that attributes their results not to loss aversion, but to differences between choice alternatives in delay of reinforcement.

Essential value of cocaine and food in rats: tests of the exponential model of demand.

RATIONALE: To provide a prospective test of the predictive adequacy of the exponential model of demand (Hursh and Silberberg, Psych Rev 115(1):186-198, 2008). OBJECTIVES: In Experiment 1, to measure the 'essential value' (the propensity to defend consumption with changes in price) of cocaine and food in a demand analysis (functional relation between price and consumption) by means of the exponential model; in Experiment 2, to test whether the model's systematic underestimation of cocaine consumption in Experiment 1 was due to weight loss; and in Experiment 3, to evaluate the effects of cocaine on the essential value of food. MATERIALS AND METHODS: In Experiment 1, demand curves for food and cocaine were determined by measuring consumption of these goods in a multiple schedule over a range of fixed ratios; in Experiment 2, a demand curve for only cocaine was determined; and in Experiment 3, demand for food was determined in the absence of cocaine. RESULTS: In Experiment 1, the exponential equation accommodated high portions of variance for both curves, but systematically underestimated cocaine demand; in Experiment 2, this predictive underestimation of the equation was eliminated; and in Experiment 3, the essential value of food was greater than in Experiment 1. CONCLUSIONS: The exponential model of demand accommodated the data variance for all cocaine and food demand curves. Compared to food, cocaine is a good of lower essential value.

Early maternal separation and sex differences in the aversive effects of amphetamine in adult rats.

Early life stress increases vulnerability to psychostimulant abuse, sometimes in a sex-dependent manner. These effects are presumably produced by modulation of neurobiological reward mechanisms; however, drug intake is also influenced by sensitivity to the drug's aversive properties, and little is known about the effects of early life stress on stimulant aversion. To assess this possibility, Sprague-Dawley rat litters experienced daily separation from the dam for 3 h (MS) or 15 min (H) on post-natal days 2-14; control litters (AFR) experienced twice-weekly routine animal facility care only. As adults, the animals were tested for conditioned taste aversions (CTA) induced by 1.5, 2.0 or 3.0 mg/kg d-amphetamine administered intraperitoneally over three acquisition trials followed by six drug-free extinction trials (n=7-8/sex/dose/rearing group). All groups acquired significant aversions compared to their vehicle-treated controls, but differential rearing had no effect on CTA acquisition or extinction. Collapsed across rearing groups, females exhibited significantly stronger aversions and slower extinction than their male counterparts at the low 1.5 mg/kg dose, and unlike the males, failed to fully extinguish relative to their vehicle controls at 1.5 and 2.0 mg/kg. These data underscore the importance of sex differences in assays of stimulant abuse liability, and further support the hypothesis that the effects of post-natal stress on the reinforcing efficacy of psychostimulants may be predominantly due to modulation of reward mechanisms.

Reduction of cocaine seeking by a food-based inhibitor in rats.

Environmental stimuli can exert a powerful influence over drug seeking and taking. For example, previous experiments found that combining multiple drug-related stimuli tripled drug seeking and doubled drug intake (L. V. Panlilio, S. J. Weiss, & C. W. Schindler, 1996, 2000), whereas a signal for the absence of cocaine (i.e., a drug-related inhibitor) dramatically reduced cocaine seeking in rats by over 90% (D. N. Kearns, S. J. Weiss, C. W. Schindler, & L. V. Panlilio, 2005). In the present experiment, a signal for the absence of food created through the A+/AB- conditioned inhibition paradigm also suppressed responding for cocaine by approximately 90%. Symmetrically, a signal for the absence of cocaine (i.e., a cocaine-based inhibitor) suppressed food seeking to a similar degree. These findings, consistent with the appetitive-aversive interaction theory of motivation, suggest that using inhibitors based on nondrug appetitive reinforcers might be a practical method of reducing drug seeking in human drug abusers and should be seriously considered for clinical test and application.

Mark tests for mirror self-recognition in capuchin monkeys (Cebus apella) trained to touch marks.

In Experiment 1, three capuchin monkeys (Cebus apella) were exposed to a mirror in their home cage for 3 days and then given food treats for touching orange marks located on the surface of an experimental chamber. Following training, a mirror was added to the chamber to see if the monkeys would use it to guide non-reinforced contacts with an orange mark on their foreheads that was only visible as a mirror reflection (mark test). Two monkeys touched the head-mark more often with the mirror present than absent, but no mark touches were emitted while looking at the mirror. In Experiment 2, the monkeys were rewarded for touching orange marks on their bodies that were directly visible, followed by another head-mark test. Again, two monkeys touched the mark more often with the mirror present than absent, but these contacts were not emitted while looking at the mirror. Since facing the mirror while mark touching was not required for reinforcement during training, Experiment 3 further tested the possibility that increased mark touching in the presence of the mirror during Experiments 1 and 2 was the result of a memorial process. For this, a final, novel mark test was conducted using an orange mark on the neck that was only visible as a reflection (Experiment 3). No monkeys passed this test. These are the first mark tests given to capuchin monkeys. The results are consistent with the finding that no monkey species is capable of spontaneous mirror self-recognition. The implications of sequential training and mark testing for comparative evaluations of mirror self-recognition capacity are discussed.

Separation stress, litter size, and the rewarding effects of low-dose morphine in the dams of maternally separated rats.

Potential differences in sensitivity to the rewarding effects of morphine as a function of litter separation stress were assessed in post-weaning rat dams. During the first two weeks postnatal, Sprague-Dawley rat litters were subjected to daily 15- or 180-min sessions of dam-pup separation while control litters only experienced twice-weekly animal facility care. One week after weaning, the dams (n=7 per group) underwent a fully unbiased conditioned place preference (CPP) procedure to 1 mg/kg subcutaneous morphine. CPP responses after each conditioning cycle were recorded. Rates of acquisition and asymptotic levels of CPP were comparable in all groups; however, an inverse relationship between litter size and magnitude of morphine CPP was revealed. Although these initial data indicate no differential sensitivity to the rewarding effects of low-dose morphine produced by the stress of litter separation, this assessment of litter size and drug-induced place conditioning in post-weaning litter-separated dams is the first of its kind. Potential effects of other doses, drugs of abuse and post-partum manipulations remain to be evaluated within this emerging etiological model.