Transitive inference in rats (Rattus norvegicus).

Although Piagetian theory proposes that the ability to make transitive inferences is confined to humans above age 7 yrs, recent evidence has suggested that this logical ability may be more broad based. In nonverbal tests, transitive inference has been demonstrated in preschool children and 2 species of nonhuman primates. In these experiments, evidence of transitive inference in rats is demonstrated. An ordered series of 5 olfactory stimuli (A??E and A?>?F). The possibility that logical transitivity may reflect a form of spatial paralogic rather than formal deductions from a syllogistic–verbal system is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of preexperimental experience on social discrimination in rats (Rattus norvegicus).

The authors used laboratory rats (Rattus norvegicus) of known relatedness and contrasting familiarity to assess the potential effect of preexperimental social experience on subsequent social recognition. The authors used the habituation-discrimination technique, which assumes that multiple exposures to a social stimulus (e.g., soiled bedding) ensure a subject discriminates between the habituation stimulus and a novel stimulus when both are introduced simultaneously. The authors observed a strong discrimination if the subjects had different amounts of preexperimental experience with the donors of the 2 stimuli but a weak discrimination if the subjects had either equal amounts of preexperimental experience or no experience with the stimuli. Preexperimental social experience does, therefore, appear to influence decision making in subsequent social discriminations. Implications for recognition and memory research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postsuckling behavioral arousal in weanling rats (Rattus norvegicus).

Twenty-day-old litters and their dams were observed in seminatural habitats consisting of a nest compartment and adjacent open field that contained powdered rat chow. It was found that pups displayed marked bursts of activity after suckling. Independent feeding reliably followed nursing bout termination (Experiment 1). Nipple withdrawal, with or without milk transfer, induced behavioral arousal whereas withdrawal of thermotactile and conspecific odor cues did not (Experiments 2-3). Increased thermogenesis was observed following milk transfer (Experiment 4). Finally, preweanling pups (10- to 12-day-olds) also displayed postsuckling arousal within the confines of the nest; full locomotor expression of this arousal was not evident until weaning age (Experiment 5). It was concluded that postsuckling arousal in weanlings functions to stimulate activities performed away from the nest and suckling, propelling pups into the field where feeding begins. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual free behavior in male rats (Rattus norvegicus).

Male rats ( Rattus norvegicus) were given continuous access to estrous female rats for 24 hrs each day for 10 days. During the 1st 12 hrs, the rats achieved an average of 10 ejaculations, followed by a 1- to 2-day period with little sexual activity. During the last 7 days, the rats maintained a reasonably stable equilibrium level of 3 ejaculations per day. These occurred predominantly during the dark phase of the diurnal cycle, they frequently occurred in a cluster, and they usually occurred shortly after the introduction of a novel estrous female. Except for quantitative differences, these results are generally consistent with conventional research but systematically extend the generality of the results to the context of the free behavior situation. The availability of sexual activity had no appreciable effect on food and water intake, but it did decrease the amount of running activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The von Restorff effect in rats (Rattus norvegicus).

Two experiments examined the functional equivalence of memory in the rat (Rattus norvegicus) with memory in humans for serially presented items. Memory was assayed with an 8-arm radial maze, in which rats were allowed access to 5 arms of the maze and were then removed. Following a retention interval of 16 min, the rats were replaced in the maze and allowed to retrieve pellets from the 3 unvisited arms. The errors in reentering previously visited arms were noted. Both primacy and recency effects were found as with humans. Presenting a stimulus change after entry to 1 of the maze arms improved recall for that arm relative to when no change occurred. This effect was found using both handling and tone cues, and irrespective of whether the change consisted of presentation or nonpresentation of the cue. These results suggest that rats are subject to a von Restorff-like effect similar to that in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recognition of food by individual, food-naive, weaning rats (Rattus norvegicus).

To control and observe first feeding experiences, pups were reared without access to food. At weaning age, individual pups received simultaneous access to a palatable, noncaloric diet and a similar diet containing starch. Each diet contained a flavor cue. Within 20 min of sampling both diets pups preferentially ingested the caloric alternative. Further tests indicated that pups learned a preference for flavor cues paired specifically with ingestion of starch. In caloric discrimination tests in which the diets were not distinguished by artificial flavors, pups did not show the rapid preference for the caloric diet seen in earlier experiments. We suggest that recognition and preference for the caloric diet is based on its rapid postingestive effects rather than readily preferred sensory features of the starch. Our findings demonstrate the abilities of individual, food-naive pups to rapidly recognize food and indicate a role for associative learning in the onset of independent feeding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory conditioning of sexual behavior in the male rat (Rattus norvegicus).

The role of classical conditioning in the copulatory preferences of male Long-Evans rats (Rattus norvegicus) was examined by pairing a neutral olfactory stimulus (almond odor) with female reproductive status. During training trials, the males were given access to scented or unscented females that were either sexually receptive or unreceptive. Subsequently, copulatory preferences were tested in males given simultaneous access to 2 receptive females, 1 scented and 1 not. Males trained with scented-receptive females displayed an ejaculatory preference for the scented female. Males trained with scented-unreceptive females or with unscented-receptive females displayed an ejaculatory preference for the unscented female. Males displayed no preference when scent and reproductive status were paired randomly. These results demonstrate that classical conditioning produces an ejaculatory preference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time course of postpartum aggression in rats (Rattus norvegicus).

The time course of postpartum aggression was examined in primiparous Long-Evans rats (N?=?77). Individually housed lactating females (n?=?7 per condition) were randomly assigned to 1 of 11 conditions (day of testing), with each subject tested once between Day 0 (the day of parturition) through Day 20 postpartum. Duration of aggression was highest and latency to attack was shortest on Day 0, with all dams attacking an unfamiliar intruding male during 10-min tests. The proportion of dams engaging in attack remained high through the end of the first week of lactation, but decreased sharply during the third week postpartum. The findings indicate that the probability and intensity of maternal aggression is closely associated with the time since parturition at which tests are given. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual differences in the behavior of rats (Rattus norvegicus).

Male and female hooded rats were evaluated individually for performance in burrowing, food hoarding, exploration, and insect predation in the laboratory. The results were that (a) performance in each of these behaviors was distributed over a wide range; (b) females as a group had significantly better burrowing and insect predation performance than did males; (c) there were significant correlations between individual performance in each of these behaviors in two series of tests held 30 days apart; and (d) no evident and systematic correlations between individual performance in different kinds of behavior were detected. These and other results in the literature support the idea that behavioral performance in nonprimate mammals is not stereotyped. On the contrary, individuals tend to have conspicuous behavioral interactions with the environment, and this characteristic tends to be stable, under our conditions, for periods of at least 1 month. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Food stealing by young Norway rats (Rattus norvegicus).

Six experiments were undertaken to explore factors affecting young rats' (Rattus norvegicus) frequencies of stealing food from conspecifics when identical food is available in surplus. It was found that (a) rats would walk across a bed of pellets to steal the particular pellet a peer was eating, (b) frequency of stealing within a pair did not decrease over days, (c) rats stole unfamiliar foods more frequently than familiar foods, (d) younger rats stole from older rats more frequently than older rats stole from younger ones, (e) hungry rats stole more frequently than replete rats, and (f) rats that had stolen a pellet of unfamiliar food from an anesthetized conspecific subsequently exhibited an enhanced preference for that food. Results suggest that food stealing is a mode of active seeking of information about what foods to eat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex and social play in juvenile rats (Rattus norvegicus).

Four experiments were conducted to examine the effects of pretest social isolation, sex of the social stimulus, and test cage familiarity on sex differences in play fighting in 156 juvenile Long-Evans rats. Reliable sex differences were found only when Ss were tested after 6 days of isolation in undisturbed cages (Exp III). In contrast to weak sex effects, pretest isolation and test cage familiarity were robust variables influencing levels of play fighting in juveniles of both sexes. Results are discussed in reference to procedural differences among experimental approaches that have examined sex differences in social play. It is suggested that social investigatory behavior and play behavior appear to be reciprocally related. Hence, the sex difference in social play is accompanied by an apparent reversal in the sex effect seen with social investigation. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrasounds during agonistic interactions between female rats (Rattus norvegicus).

Defensive and vocal behaviors of 18 female Long-Evans rats (Rattus norvegicus) in encounters with aggressive, lactating conspecifics were examined in order to determine if female rats emit ultrasounds during agonistic interactions and to characterize any such calls. The Ss, selected during estrus or diestrus, were exposed to 1-min attacks at 25-min intervals. Between attacks the Ss were threatened by the aggressor but protected by a wire-mesh cage. Female rats emitted both high- (32–60 kHz) and low-frequency (20–32 kHz) ultrasonic calls in agonistic encounters, with the rate of high-frequency calls enhanced during estrus. Low-frequency ultrasounds were shorter in duration and higher in frequency than those emitted by male rats in similar conditions. It is concluded that female rats emit ultrasonic calls during defensive responding and that the characteristics and rate of calling vary as functions of sex and gonadal hormone state. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Theoretical note on the moral development of rats (Rattus norvegicus).

Rats trained to eat a fixed number of food items from a larger array began to consume additional pieces of food when the experimenter was no longer available to punish errors (Davis & Bradford, 1988). When such departures from "correct" behavior are viewed in terms of Kohlberg's (1976) schema of moral development, it appears that rats are functioning in the Preconventional mode. However, it may be inappropriate to view rats as a morally deficient species. Although notions of morality need not be confined to human behavior, numerous problems are associated with comparing the residual effects of punishment ("resistance to temptation") both within or between species. The results of such comparisons and their implications for morality must be evaluated with utmost caution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social identification of toxic diets by Norway rats (Rattus norvegicus).

48 naive female Long-Evans rats (observers) interacted with 2 conspecifics (demonstrators [n?=?96]) that had recently eaten a diet unfamiliar to the observer; ate 2 unfamiliar foods in succession, one of which was the food its demonstrators had eaten; suffered toxicosis; and were offered a simultaneous choice between the 2 diets they had eaten prior to toxicosis induction. During the choice test, observers exhibited an aversion to that diet their respective demonstrators had not eaten. It is suggested that exposure of a rat to conspecifics that have eaten a diet can act, as does actual ingestion of a diet, to reduce that diet's subsequent associability with toxicosis and that interaction with conspecifics may provide an alternative to individual trial-and-error learning in identification of toxic foods by rats that ingest a number of novel foods in succession before becoming ill. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perioral somatosensory determinants of nursing behavior in Norway rats (Rattus norvegicus).

Prior to assuming the upright crouching posture over their pups during nursing bouts, lactating rats typically engage in several oral behaviors, including nuzzling, licking and rearranging pups. By acutely depriving dams of various aspects of perioral stimulation from pups (with anesthesia of the mystacial pads or of the tongue, with mouth suturing, or with muzzling), we found the following: (1) distal stimulation from pups maintains proximity-seeking behavior, but is insufficient to stimulate nursing behavior. (2) Lack of tongue feedback decreases pup licking and hastens the onset of crouching. (3) Snout, but not tongue, contact with pups is required for hovering over them. (4) The position of the dam while hovering over her litter enables the pups to gain access to her ventrum, thereby provoking her upright, crouching posture. (5) Older pups are capable of bypassing dam's perioral attentions and stimulating crouching directly by burrowing under the dam's ventrum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social transmission of food preferences in adult hooded rats (Rattus norvegicus).

When given a choice between 2 novel diets, rats show a marked preference for the diet that a paired conspecific has been eating. Four experiments were conducted to investigate this transmission of a food preference from one rat to another. Ss were 340 male Long-Evans hooded rats that were paired into observers and demonstrators. Demonstrators were presented with 2 novel foods, one adulterated with quinine sulfate, after which the observers were presented with the same novel diets, neither of which was adulterated with quinine. These studies suggest that (a) the effect is socially mediated, (b) the learning is very rapid, and (c) the preference can last for at least 5 days. Results are discussed in the context of other instances of social transmission of food-related behaviors and in terms of social learning in general. Findings stress the importance of divising animal learning paradigms in accord with the natural history of the animal being studied. (43 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Life-span changes in the copulatory behavior of male rats (Rattus norvegicus).

Studied the copulatory behavior of 36 5-, 10-, 15-, and 20-mo old sexually naive male Long-Evans rats during 2-hr tests with receptive females. There was no apparent change in sexual arousal as measured by latency to initiate copulation across age, with Ss from all groups exhibiting comparable latencies to 1st mount and 1st mount with intromission. The numbers of ejaculations achieved were also similar across ages. Significant age differences were found for frequency of mounts, with 20-mo olds having the highest mean frequency. The persistent mounting by older Ss appeared to account for significant group differences in interintromission interval and ejaculation latency. It is suggested that motor deficits may impair the ability of older Ss to achieve intromission, increasing the number of mount bouts as well as the number of mounts for each bout, thus extending the length of each copulatory series. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in mating vocalizations over the ejaculatory series in rats (Rattus norvegicus).

Rats (Rattus norvegicus) produce ultrasonic calls during mating. We examined changes in the structure and pattern of such vocalizations over the ejaculatory series. In Experiment 1, vocalizations were recorded from 11 pairs of rats through 3 ejaculatory series and analyzed spectrographically. We classified 4 categories of call by spectral frequency and duration. Calls of low frequency, long duration, and high intensity occurred more often shortly before the ejaculation and were associated with mounting without intromission, a behavior that often occurs shortly before ejaculation. The high-frequency calls did not vary in number across the series. In Experiment 2, vocalizations were recorded from males paired with devocalized females. Males produced all vocalization patterns produced by pairs in Experiment 1. Results suggest that most pre-ejaculatory calls are produced by males and may potentially affect female sexual behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of spatial food distribution on search behavior in rats (Rattus norvegicus).

To analyze how search strategies are adapted according to the geometric distribution of food sources, the authors submitted rats to a search task in which they had to explore 9 food trays in an open field and avoid visiting already-depleted trays. Trays were spatially arranged in 4 independent configurations: a cross, a 3 × 3 matrix, 3 clusters of 3 trays each, and a random configuration. Rats exhibited differential search efficiency as a specific effect of the susceptibility of the configurations to being explored in a principled way: Crosses were first, matrices or clusters were in the middle, and random configurations were last. Although no exhaustive searches or highly principled patterns were observed in any of the configurations, performances improved as the sessions went by. Thus, structural affordances of the environment influence the construction not only of search strategies but also of information linked to where the reward is. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Numerical discrimination by rats (Rattus norvegicus) using body and vibrissal touch.

Three experiments were performed to test if tactile stimuli could serve as the basis for a numerical discrimination in rats (Rattus norvegicus). In Experiment 1, touch delivered symmetrically to both sides of the animal's body yielded no evidence of numerical discrimination. In Experiment 2, the restriction of tactile cues to one side of the animal's body resulted in marginally better results, although performance remained below conventional levels of significance. In Experiment 3, tactile contact with the animal's vibrissae yielded statistically significant evidence of numerical processing. Subjects learned to enter one arm of a Y-maze when three vibrissal deflections were presented, and the other arm when either two or four stimuli occurred. The demonstration of a two-three-four discrimination extends the use of this relatively complex intermediate number procedure from a previous demonstration in rats involving auditory stimuli (Davis & Albert, 1986) and indicates for the first time in any species that touch may be used as the basis for numerical behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)