Auditory-visual cross-modal perception of communicative stimuli in Tufted Capuchin Monkeys (Cebus apella).

Research on cross-modal performance in nonhuman primates is limited to a small number of sensory modalities and testing methods. To broaden the scope of this research, the authors tested capuchin monkeys (Cebus apella) for a seldom-studied cross-modal capacity in nonhuman primates, auditory-visual recognition. Monkeys were simultaneously played 2 video recordings of a face producing different vocalizations and a sound recording of 1 of the vocalizations. Stimulus sets varied from naturally occurring conspecific vocalizations to experimentally controlled human speech stimuli. The authors found that monkeys preferred to view face recordings that matched presented vocal stimuli. Their preference did not differ significantly across stimulus species or other stimulus features. However, the reliability of the latter set of results may have been limited by sample size. From these results, the authors concluded that capuchin monkeys exhibit auditory-visual cross-modal perception of conspecific vocalizations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discriminative Stimulus, Reinforcing, Physical Dependence, and Antinociceptive Effects of Oxycodone in Mice, Rats, and Rhesus Monkeys.

Despite oxycodone's (4,5-epoxy-14-hydroxy-3-methoxy-17-methylmorphinan-6-one) history of clinical use and the attention it has received as a drug of abuse, few reports have documented its pharmacology's relevance to its abuse or its mechanism of action. The purposes of the present study were to further characterize the analgesic effects of oxycodone, its mechanism of action, and its effects in terms of its relevance to its abuse liability. The results indicate that oxycodone had potent antinociceptive effects in the mouse paraphenylquinone writhing, hot-plate, and tail-flick assays, in which it appeared to be acting as a μ-opioid receptor agonist. It generalized to the heroin discriminative stimulus and served as a positive reinforcer in rats and completely suppressed withdrawal signs in morphinedependent rhesus monkeys. These results suggest that the analgesic and abuse liability effects of oxycodone are likely mediated through μ-opioid receptors and provide the first laboratory report of its discriminative stimulus, reinforcing, and morphine cross-dependency effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Category Learning in Rhesus Monkeys: A Study of the Shepard, Hovland, and Jenkins (1961) Tasks.

In influential research, R. N. Shepard, C. I. Hovland, and H. M. Jenkins (1961) surveyed humans' categorization abilities using tasks based in rules, exclusive-or (XOR) relations, and exemplar memorization. Humans' performance was poorly predicted by cue-conditioning or stimulus-generalization theories, causing Shepard et al. to describe it in terms of hypothesis selection and rule application that were possibly supported by verbal mediation. The authors of the current article surveyed monkeys' categorization abilities similarly. Monkeys, like humans, found category tasks with a single relevant dimension the easiest and perceptually chaotic tasks requiring exemplar memorization the most difficult. Monkeys, unlike humans, found tasks based in XOR relations very difficult. The authors discuss the character and basis of the species difference in categorization and consider whether monkeys are the generalization-based cognitive system that humans are not. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mu/kappa opioid interactions in rhesus monkeys: Implications for analgesia and abuse liability.

Mu opioid receptor agonists are clinically valuable as analgesics; however, their use is limited by high abuse liability. Kappa opioid agonists also produce antinociception, but they do not produce mu agonist-like abuse-related effects, suggesting that they may enhance the antinociceptive effects and/or attenuate the abuse-related effects of mu agonists. To evaluate this hypothesis, the present study examined interactions between the mu agonist fentanyl and the kappa agonist U69,593 in three behavioral assays in rhesus monkeys. In an assay of schedule-controlled responding, monkeys responded under a fixed-ratio 30 (FR 30) schedule of food presentation. Fentanyl and U69,593 each produced rate-decreasing effects when administered alone, and mixtures of 0.22:1, 0.65:1, and 1.96:1 U69,593/fentanyl usually produced subadditive effects. In an assay of thermal nociception, tail withdrawal latencies were measured from water heated to 50 °C. Fentanyl and U69,593 each produced dose-dependent antinociception, and effects were additive for all mixtures. In an assay of drug self-administration, rhesus monkeys responded for intravenous drug injection, and both dose and FR values were manipulated. Fentanyl maintained self-administration, whereas U69,593 did not. Addition of U69,593 to fentanyl produced a proportion-dependent decrease in rates of fentanyl self-administration. Moreover, addition of U69,593 increased the sensitivity of fentanyl self-administration to increases in the FR value. Taken together, these results suggest that simultaneous activation of mu and kappa receptors, either with a mixture of selective drugs or with a single drug that targets both receptors, may reduce abuse liability without reducing analgesic effects relative to selective mu agonists administered alone. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is a sense of inequity an ancestral primate trait? Testing social inequity in cotton top tamarins (Saguinus oedipus).

To address a controversy in the literature concerning whether monkeys show an aversion to inequity, individuals of a New World monkey species, cotton top tamarins (Saguinus oedipus) were tested in an offering task and in a bartering task. At issue was whether the monkeys rejected rewards because of a violation of expectancy of the preferred reward, or whether they rejected rewards because of a sensitivity to socially mediated inequity. The data from both tasks indicated that the subjects were more likely to reject when preferred rewards were presented, either because of another animal eating the reward (the social condition) or because of rewards being presented but inaccessible. The bartering task led to the only behavioral indication of aversion due specifically to social inequity, which was demonstrated when tamarins' sensitivity to the difference in rewards increased with exposure to other tamarins working to receive the preferred rewards. The results suggest that social inequity aversion will be assessed by tamarins, and possibly by other primates, only under conditions of limited resources and a requirement of work, which may make the situation a bit more competitive and thus drives attention toward both social and reward evaluation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive preconditions for responses to fairness: An object retrieval test of inhibitory control in capuchin monkeys (Cebus apella).

The authors explore the evolution of one cognitive mechanism required for altruistic behavior: the capacity to inhibit prepotent responses. Specifically, the authors used an object retrieval task to investigate whether capuchins (Cebus apella) can inhibit a prepotent strategy of reaching directly for a food reward. Success in this task varies across species and across development, but is also known to depend critically on the maturity of dorsolateral prefrontal cortex, the cortical area implicated in rejecting small payoffs in an Ultimatum Game. Capuchins easily inhibit the tendency to reach directly for food in the object retrieval task, successfully employing an alternative reaching strategy even in the first session of performance. This contrasts with the performance of closely related tamarin monkeys, who performed less well despite extensive training. These results provide the first evidence that capuchins likely exhibit human-like inhibitory control in tasks previously linked to the function of the dorsolateral prefrontal cortex, such as the Ultimatum Game. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory for “what”, “where”, and “when” information in rhesus monkeys (Macaca mulatta).

The present study examined working memory for what, where, and when information in rhesus monkeys (Macaca mulatta) using a computerized task. In Experiment 1, monkeys completed three delayed matching-to-sample (DMTS) tasks: (1) identity DMTS, (2) spatial DMTS, and (3) temporal DMTS. In Experiment 2, the identity and spatial tasks were combined so that monkeys had to report both what and where information about an event. In Experiment 3, the identity, spatial, and temporal tasks were combined to examine what-where-when memory integration. The rhesus monkeys reported all three components of the events, and there was some evidence suggesting that these components were integrated in working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of triazolam, 8-OH-DPAT, and buspirone on repeated acquisition in squirrel monkeys.

The nonserotonergic benzodiazepine, triazolam, was compared with two 5-HT1A receptor agonists, 8-OH-DPAT and buspirone, in squirrel monkeys responding under a repeated-acquisition procedure. In each session, subjects acquired a 4-response sequence by responding sequentially on 3 keys in the presence of 4 discriminative stimuli (colors). Response sequences for each session were maintained by food presentation under a second-order fixed-ratio schedule. Errors produced a brief time-out but did not reset the sequence. In general, all of the drugs produced dose-dependent decreases in overall response rate and increases in the percentage of errors as the cumulative dose was increased. Together, these results indicate that 5-HT1A receptor agonists disrupt learning in squirrel monkeys by producing rate-decreasing and error-increasing effects in a manner comparable with the nonserotonergic benzodiazepine triazolam. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Opioids and attachment in rhesus macaque (Macaca mulatta) abusive mothers.

This study investigated the role of the endogenous opioid system in maternal and affiliative behavior of group-living rhesus macaque (Macaca mularta) mothers with a history of abusive parenting. 18 mothers received an injection of the opioid antagonist naltrexone or saline for 5 days per wk for the first 4 wks of the infant's life. After treatment, mother-infant pairs were focally observed. Naltrexone did not significantly affect infant abuse or other measures of maternal behavior. Naltrexone increased the amount of grooming received by mothers from other group members and reduced the mothers' rate of displacement activities such as scratching, yawning, and self-grooming. These results concur with previous primate studies in suggesting that opioids mediate the rewarding effects of receiving grooming and affect anxiety-related behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)