Linking of serially ordered lists by macaque monkeys (Macaca mulatta): List position influences.

Five monkeys (Macaca mulatta) were trained on 2 sets of 3 5-item serially ordered lists. Then, each set was either linked or not in a counterbalanced, within-subject design. Linking entailed training on the 2 pairs that ordered the 3 5-item fists into a single overall 15-item series. Choices on novel pairings after linking conditions attempted to define the unique contributions of knowledge of within-list ordinal position and between-lists link training. With linkage, the series was immediately treated as a 15-item ordered list. Without linkage, choices reflected list positions from initial learning, but continued testing with directional reward yielded gradual ordering into a 15-itern list. Apparently, monkeys remembered and used initial list-position information, but linkage allowed inference of an integrated serial relationship among items. Results supported primate list memory as an organizational process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social recovery of monkeys isolated for the first year of life: I. Rehabilitation and therapy.

Previous research demonstrated that 12 mo of total social isolation initiated at birth produced severe and seemingly permanent social deficits in rhesus monkeys. Such monkeys exhibited self-clasping, self-mouthing, and other stereotypic, self-directed responses. Recent research has indicated that 6-mo-isolated monkeys could develop social behaviors if exposed to younger, socially unsophisticated "therapist" monkeys. In the present experiment, 4 12-mo isolate-reared monkeys developed appropriate species-typical behavior through the use of adaptation, self-pacing of visual input, and exposure to 4 younger "therapist" monkeys. Adaptation enabled the isolate Ss to become familiar with their postisolation environment, while self-pacing facilitated their watching the therapist Ss' social interactions. The isolates showed a marked decrease in self-directed behaviors following extensive intimate contact with the therapists. Species-typical behaviors significantly increased during this period, so that the isolate behavioral repertoire did not differ substantially from the therapist behavioral repertoire by the end of the therapy period. Results clearly fail to support a critical period for socialization in the rhesus monkey, and an alternative environment-specific learning hypothesis is proposed. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex, Age, and Training Modulate Spatial Memory in the Rhesus Monkey (Macaca mulatta).

The authors tested 90 rhesus monkeys (Macaca mulatta) on a task of spatial memory, the spatial Delayed Recognition Span Test. The results showed that performance declined significantly with age, males had greater scores than females, and the rate of apparent decline with age was greater in males than in females. Both working and reference memory declined with age, but only working memory showed sex differences. The authors compared these data with that of 22 monkeys who were trained on a simpler version of the task before formal testing. Training had no effect on males but dramatically improved working memory in young females. The results confirm a male advantage in spatial working memory at a young age and confirm a greater decline with age in males than in females. It is important to note that prior training completely reverses the deficits of young females. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

How do tufted capuchin monkeys (Cebus apella) understand causality involved in tool use?

Four tufted capuchin monkeys (Cebus apella) were trained to choose from 2 hook-like tools, 1 of which successfully led to collecting food, whereas the other did not because of inappropriate spatial arrangement of the tool and the food. In Experiment 1, all of the monkeys successfully learned the basic task. The monkeys performed successfully with tools of novel colors and shapes in Experiments 2-5. These results demonstrate that the monkeys used the spatial arrangement of the tool and the food as a cue. However, they failed when there were obstacles (Experiment 6) or traps (Experiment 7) on the path along which she monkeys dragged tools. These results may suggest that capuchin monkeys understand the spatial relationship between 2 items, namely, food and. the tool, but do not understand the spatial relationship among 3 items, namely, food, tool, and the environmental condition. The possible role of stimulus generalization is also considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Subdivisions of inferior temporal cortex in squirrel monkeys make dissociable contributions to visual learning and memory.

Inferior temporal cortex of squirrel monkeys consists of caudal (ITC), intermediate (ITI), and rostral (ITR) subdivisions, possibly homologous to TEO, posterior TE, and anterior TE of macaque monkeys. The present study compared visual learning in squirrel monkeys with ablations of ITC; ITI and ITR (group ITRd); or ITI, ITR, and more ventral cortex, including perirhinal cortex (group ITR+), with visual learning in unoperated controls. The ITC monkeys had significant impairments on pattern discriminations and milder deficits on delayed nonmatching to sample (DNMS) of objects. The ITRd monkeys had deficits on some pattern discriminations but not on DNMS. The ITRd monkeys were significantly impaired on DNMS and some pattern discriminations. These results are similar to those found in macaques and support the proposed homologies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of age on cerebrospinal fluid oxytocin levels in free-ranging adult female and infant rhesus macaques.

There is growing interest in examining oxytocin and social functioning in human and non-human primates. Studies of human oxytocin biology are typically restricted to peripheral assessments because opportunities to collect cerebrospinal fluid (CSF) are rare. Several studies have examined CSF oxytocin levels in captive adult primates, but none to our knowledge have been conducted under free-ranging conditions and inclusive of infants. The main goal of this study was to establish feasibility of quantifying CSF oxytocin levels in free-ranging adult female and infant rhesus monkeys living on Cayo Santiago, PR. CSF oxytocin levels were examined in relation to individuals' demographic and reproductive characteristics as well as plasma cortisol levels. CSF oxytocin concentrations ranged from 36.02 to 134.41 pg/ml in adult females (ages 7–26 years; N = 31) and 35.94 to 77.3 pg/ml in infants (ages 38–134 days; N = 17). CSF oxytocin levels were positively correlated with adult female age and negatively correlated with infant age. The former correlation was driven by reproductive status. CSF oxytocin levels were unrelated to dominance rank or plasma cortisol levels. In contrast to a previous study of plasma oxytocin concentrations in this population, CSF oxytocin levels did not differ significantly between lactating and non-lactating females. These findings: 1) provide feasibility data for examining CSF oxytocin levels in free-ranging non-human primates and 2) indicate that CSF oxytocin levels may be a biomarker of age-related central nervous system changes across lifespan development. Research is now required to examine CSF oxytocin levels in the context of social functioning in free-ranging rhesus monkeys. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term effects of neonatal medial temporal ablations on socioemotional behavior in monkeys (Macaca mulatta).

Socioemotional abnormalities, including decreased social interactions and increased self-directed activity, were reported when rhesus monkeys with neonatal ablations of either the medial temporal lobe (AH) or the inferior temporal cortex (TE) were paired with unoperated peers at two and six months of age, though these abnormalities were more severe in Group AH (Bachevalier et al., 2001). As adults (Experiment 1), the monkeys were re-evaluated in the same dyads and their reactivity to novel toys, social status, and reactions to separation were also assessed. Group TE now showed only few if any of the abnormal behaviors observed in infancy. In contrast, Group AH continued to display decreased social interactions and increased self-directed activity and showed also increased submission and reduced responses to separation, but normal reactivity to novel toys. To determine whether this degree of socioemotional impairment was less severe than that produced by the same damage in adulthood, we assessed dyadic social interactions of monkeys raised until adulthood in laboratory conditions similar to those in Experiment 1 and then given the AH ablations (Experiment 2). Two months postoperatively these monkeys showed a small reduction in social interactions that became more pronounced six months postoperatively, yet remained less severe than that seen in the infant-lesioned monkeys. No other socioemotional effects, except for an increase in food/water consumption, were observed. The finding that neonatal AH lesions produce more severe socioemotional disturbances than the same lesion in adulthood is the reverse of the effect commonly reported for other cognitive functions after cerebral damage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)