Thermoregulatory behavior in infant Norway rats (Rattus norvegicus) and Syrian golden hamsters (Mesocricetus auratus): arousal,orientation, and locomotion

The responses of 2- and 8-day-old rats (Rattus norvegicus) and hamsters (Mesocricetus auratus) to thermal stimulation were assessed in 4 experiments. In Experiment 1, the surface underlying the pup was cooled, and the latency to escape to a region of warmth was measured. Experiment 2 required pups to locomote farther to gain access to warmth. Experiment 3 was similar to Experiment 1 except the underlying surface was heated. Finally, in Experiment 4, locomotor behavior was assessed during isothermal cooling in which there was no possibility for escape. In general, hamsters exhibited more rapid and robust responses to thermal stimulation than rats. A framework for interpreting these results is presented emphasizing how differences in locomotor and thermogenic capabilities influence thermoregulatory behavior under different task conditions.     

Infants' responses to mothers' imitative behaviors

Several investigators have suggested that young infants' smiles and vocalizations following their mothers' imitative behaviors might reflect infant recognition that the mother's behavior is imitative or at least contingent. This study investigated whether infants smile and vocalize more frequently subsequent to maternal imitative than non-imitative behavior during both spontaneous and imitative face-to-face interactions. Fourteen 3 1/2-month-old infants and their mothers were videotaped in these two face-to-face interaction situations. The infants vocalized more frequently during the imitative situation and infant vocalizations plus simultaneous smiling, and vocalizations occurred more often following maternal imitative than non-imitative behavior. Although these data suggest that infant vocalizations and simultaneous smiles and vocalizations may reflect the infants' recognition of maternal imitative behavior, they do not establish definitively that it is the imitation per se vs. the contingency aspect that is recognized by the infant.     

Effect of postweaning social experience on response of Siberian hamsters (Phodopus sungorus sungorus) toward young

Between 18 and 50 days of age, Siberian hamsters were housed either with same-sex littermates, opposite-sex littermates, opposite-sex littermates and parents, or opposite-sex littermates, parents, and a younger litter. When adults, these animals were presented with two 3-8-day-old pups for 8 hr, and their responses were recorded. Rearing conditions did not affect behavior of females. Males housed with female littermates in the absence of a younger litter showed fewer pup attacks and more nesting with pups than did males housed only with other males. Thus, housing with females in the early postweaning period may influence males' later (adult) responses toward pups. Only among hamsters housed with same-sex littermates did males and females differ in their response to pups, a result emphasizing that sex differences in behavior may depend on early social rearing.     

Infant clothing: Sex labeling for strangers

Labeling an infant as a boy or girl affects behavior toward the infant. While intimates know a baby's sex label and behave consistently to the baby, strangers cannot unless given a cue. Forty-eight infants and their caretakers were observed in suburban malls to see if clothing normally provides such cues; 90% of the infants were dressed in sex-typed clothes. Girls wore or carried pink (75%), yellow, ruffles, puffed sleeves, and/or dresses. Boys wore blue (79%) and/or red. Observers were able to correctly guess the sex of “labeled” infants only. Surprisingly, simultaneous caretaker interviews revealed that parents do not spontaneously mention sex as a factor in clothing choice, nor do they feel they would be very bothered by strangers' mistaking the infant's sex.     

Differences between golden hamsters (Mesocricetus auratus) and Norway rats (Rattus norvegicus) in preference for the sole diet that they are eating

D. DiBattista (2002) reported that hamsters but not rats showed reduced preferences for the sole diet they had eaten for 10 days. In the current study, the authors fed Norway rats (Rattus norvegicus) a nutritious diet for either 3 or 10 days, then tested them either immediately or 1 or 3 days later. The authors found that like golden hamsters (Mesocricetus auratus), rats exhibited reduced preferences for a prefed diet but only if tested either immediately or 1 day after prefeeding, not if tested 3 days later (when D. DiBattista tested his hamsters). Rats and hamsters differed in the longevity, not the development, of reduced preferences for a palatable food eaten for several consecutive days. Such a response might aid dietary generalists in constructing balanced diets when no single available food is nutritionally adequate.     

An experimental investigation of referential looking in free-ranging Barbary macaques (Macaca sylvanus)

The authors examined looking behavior between 15 Barbary macaque (Macaca sylvanus) infants and their mothers in the presence of a rubber snake (experimental period) and in the absence of the snake (control period). Two of the 15 infants looked referentially at their mother in the experimental period. Including both referential and nonreferential looks, the six older infants (aged 5 to 12 months) displayed a higher frequency of looks to mother than nine younger infants (aged 3 to 4.5 months) in the experimental period, but not in the control period. Older infants looked more to the mother in the experimental condition, whereas the younger infants looked more to the mother in the control condition, or looked equally in the two conditions. These results suggest that age is an important factor in determining looking behavior to mother in situations of uncertainty. Compared to hand-reared chimpanzees or human infants tested in standard social referencing paradigms, the infant macaques displayed a low rate of referential looking. Possible explanations for this are discussed. (PsycINFO Database Record (c) 2008 APA, all rights reserved).     

Organization of mating behavior in male hamsters (Mesocricetus auratus)

Factor analysis was applied to standard measures of sexual behavior in 73 male hamsters (Mesocricetus auratus) as they interacted with hormone-primed females. The results suggest that 5 factors, or conceptual mechanisms, function in the organization of the behaviors observed in the first 2 copulatory series. Of these, the 3 that relate to the behaviors in the first copulatory series were compared to those emerging from prior analyses of other rodents. These comparisons revealed similarities and differences in factor structure across species. Whereas all of these analyses identify factors related to the initiation and efficiency of copulatory behavior, hamsters seem to differ from other species in the measures that best define these factors. In addition, the copulatory rate factor that has been prominent in previous analyses of rats seems to be absent in hamsters. These results suggest that male sexual behavior in hamsters is organized differently from that in other rodents. In more general terms, they suggest that even species with generally similar copulatory patterns can show significant differences in behavioral organization, in turn suggesting the need for additional factor analytic studies to better establish the extent of these species differences.     

Change in selectivity of infant social behavior between 15 and 30 weeks

Six infants were filmed at 15 and 30 weeks of age while alone as well as in the presence of an adult (mother or stranger) who interacted with the infant or remained passive. Judges viewing samples of infant behavior tried to identify the social context in which episodes of behavior had occurred. Signal detection analysis of ratings made by the judges showed that infant behavior at both ages varied in accord with whether or not an adult was present. The identity and interactional style of the adult had only limited influence on infant behavior at 15 weeks, but judges could readily establish from the behavior of 30-week infants whether the adult was interactive or passive. Mothers were no more accurate in their ratings of social context than other judges were, even when they were observing the behavior of their own infant. Measurement of specific infant behaviors showed that the presence of the adult at both ages and the interactional style of the adult at 30 weeks exerted selective influence over rates of looking and smiling by infants. Signal detection classification was more sensitive to social context variables than microanalysis, possibly because observers had access to complex behavioral configurations.     

Caregiving behavior and interactions of prenatally depressed mothers (antidepressant‐treated and non‐antidepressant‐treated) during newborn acute pain

This exploratory study aimed to examine time‐based measures of the behaviors and interactions of prenatally depressed serotonin reuptake inhibitors (SRI)‐medicated mothers to their infant's pain (n = 10) by comparing them with similar measures obtained from prenatally depressed nonmedicated mothers and their infants (n = 10), and nondepressed mothers and their infants (n = 10). During the second trimester of their pregnancy, the 30 study mothers were assessed for depression and anxiety, with no further measures of maternal mood taken. Maternal and infant interactions were continuously videorecorded while the infant underwent a scheduled heel lance for routine blood screening that occurred when study infants were between the ages of 24 and 60 hr. Maternal behavior and infant cry, for all 30 cases, were coded second‐by‐second for the full duration of each infant's heel lance using a reliable coding system and analyzed using odds ratio and regression analyses. Infants exposed to prenatal SRIs and depressed maternal mood were more likely to have lower Apgar scores and to exhibit weak and absent cry. Even when duration of the heel lance was controlled for, women with depression during the second trimester were more likely to exhibit depressed behavior at 2 days' postpartum despite sustained SRI antidepressant treatment. Both groups of prenatally depressed mothers were more likely to exhibit diminished response to their infants' pain cue although nonmedicated mothers' expressions of depressed behavior were more similar to healthy controls. Comprehensive understanding is essential to optimize the clinical care of mothers and their infants in this complex setting. This study contributes preliminary new findings that warrant prospective and longitudinal studies to clarify further the impacts of prenatal SRI and maternal mental mood (e.g., chronic depression and anxiety) effects on the mother–infant interaction and infant pain and stress reactivity.     

Behavioral responses of juvenile rats (Rattus norvegicus) to neonates after infusion of maternal blood plasma

Individual 18- or 30-day-old male and female Wistar rats (juveniles) were continuously exposed to 3-8-day-old pups for 5 days (sensitization) after intravenous (iv) infusion of maternal blood plasma (PL group) or 5% dextrose and water (IC group) through chronically implanted cannulas and were compared with nonhandled littermate controls (NHC group). The results showed complex interactions with sex and age of the animals tested, depending upon which maternal behaviors were examined. First, plasma from parturient females selectively increased retrieving behavior in 30-day-olds, and it was more powerful in females than in males. Second, on the first day, prior to sensitization, both PL and IC 30-day-olds showed higher frequencies of retrieving, crouching, anogenital licking, and contact than did nonhandled juveniles. Third, 30-day-olds that received maternal blood plasma continued to retrieve pups, with a latency peak for retrieving occurring at 72 hours, suggesting a long-term effect of plasma not seen in control animals. Fourth, 18-day-old subjects did not generally show effects of any of our manipulations, but they did show more nest building and contact behaviors than did 30-day-old subjects. Last, we found that the iv cannulation and infusion procedures led to a persistent dissociation of retrieving behavior from play in older animals and an integration of retrieving with crouching and licking regardless of whether maternal plasma or control infusion was administered. Retrieving behavior was associated with play behaviors (charge and pounce) in younger juveniles and in older, nonhandled control animals irrespective of treatment. For these animals, no integration of retrieving occurred with other maternal behaviors.     

Social transmission of flavor preferences in two species of hamsters (Mesocricetus auratus and Phodopus campbelli)

Golden hamsters (Mesocricetus auratus) and dwarf hamsters (Phodopus campbelli) interacted with a conspecific demonstrator that had recently consumed a flavored food. When given a choice between their demonstrator's flavor and another flavor, the dwarf hamsters preferred the flavor their demonstrator had eaten. Golden hamsters did not prefer their demonstrators' diets when the demonstrators were unrelated adults or littermates, but they did when the demonstrator was their mother. Videotaping the interactions between demonstrators and observers revealed that adult golden hamsters did not investigate foods hoarded by their demonstrators whereas dwarf hamsters did. These results are interpreted in terms of the stimuli that activate feeding behavior systems in these 2 hamster species.     

DO INFANTS SHOW GENERALIZED IMITATION OF GESTURES?

Two experiments were conducted to investigate generalized imitation of manual gestures in 1- to 2-year-old infants. In Experiment 1, 6 infants were first trained four baseline matching relations (e.g., when instructed "Do this", to raise their arms after they saw the experimenter do so). Next, four novel gestures that the infants did not match in probe trials were selected as target behaviors during generalized imitation Test 1; models of these gestures were presented on unreinforced matching trials interspersed with intermittently reinforced baseline matching trials. None of the infants matched the target behaviors. To ensure that these behaviors were in the infants' motor skills repertoires, the infants were next trained to produce them, at least once, under stimulus control that did not include an antecedent model of the target behavior. In repeat generalized imitation trials (Test 2), the infants again failed to match the target behaviors. Five infants (3 from Experiment 1) participated in Experiment 2, which was identical to Experiment 1 except that, following generalized imitation Test 1, the motor-skills training was implemented to a higher criterion (21 responses per target behavior), and in a multiple-baseline, across-target-behaviors procedure. In the final generalized imitation test, 1 infant matched one, and another infant matched two target behaviors; the remaining 17 target behaviors still were not matched. The results did not provide convincing evidence of generalized imitation, even though baseline matching was well maintained and the target behaviors were in the infants' motor skills repertoires, raising the question of what are the conditions that reliably give rise to generalized imitation.     

Labels as features (not names) for infant categorization: a neurocomputational approach

A substantial body of experimental evidence has demonstrated that labels have an impact on infant categorization processes. Yet little is known regarding the nature of the mechanisms by which this effect is achieved. We distinguish between two competing accounts: supervised name-based categorization and unsupervised feature-based categorization. We describe a neurocomputational model of infant visual categorization, based on self-organizing maps, that implements the unsupervised feature-based approach. The model successfully reproduces experiments demonstrating the impact of labeling on infant visual categorization reported in Plunkett, Hu, and Cohen (2008) . It mimics infant behavior in both the familiarization and testing phases of the procedure, using a training regime that involves only single presentations of each stimulus and using just 24 participant networks per experiment. The model predicts that the observed behavior in infants is due to a transient form of learning that might lead to the emergence of hierarchically organized categorical structure and that the impact of labels on categorization is influenced by the perceived similarity and the sequence in which the objects are presented. The results suggest that early in development, say before 12 months old, labels need not act as invitations to form categories nor highlight the commonalities between objects, but they may play a more mundane but nevertheless powerful role as additional features that are processed in the same fashion as other features that characterize objects and object categories.     

Preference for novel flavors in adult golden hamsters (Mesocricetus auratus)

Although animals generally prefer to eat foods with familiar rather than unfamiliar flavors, adult golden hamsters (Mesocricetus auratus) were found to do the opposite. After having prolonged exposure to a food with a particular flavor, hamsters were allowed to select between the food with the familiar flavor and the same food with a novel flavor. Hamsters consistently ate more of the food with the novel flavor, and this preference was long-lasting and resistant to extinction. Furthermore, the novelty effect was robust, being manifested in both sexes and under a variety of experimental circumstances. In contrast, rats tested under identical conditions consistently preferred the food with the familiar flavor. The origins of the novelty effect in hamsters remain to be determined.     

Distress vocalizations in infant rats: what's all the fuss about?

Ultrasonic vocalizations emitted by infant rodents are typically characterized as cries of distress. There are two contexts that are known to reliably elicit ultrasound production: extreme cold exposure and administration of clonidine, an α₂ adrenoceptor agonist. Noting that these two contexts both entail pronounced decreases in cardiac rate, we have hypothesized that the vocalizations are acoustic by-products of a physiological maneuver, the abdominal compression reaction (ACR), that increases venous return to the heart when return is compromised. As a critical test of this hypothesis, we measured venous pressure near the right atrium in 15-day-old rats after clonidine administration. Consistent with the ACR hypothesis, emission of ultrasound was accompanied by large and reliable increases in venous pressure and, therefore, venous return. These results provide strong, direct support for the ACR hypothesis and, by doing so, underscore the potential pitfalls of anthropomorphic interpretations of the vocalizations of infant rats.     

Mother-infant interactions in western Lowland Gorillas (Gorilla gorilla gorilla): spatial relationships,communication, and opportunities for social learning

This study investigated mother-infant interactions in lowland gorillas (Gorilla gorilla gorilla) with particular focus on the relative role of mothers and infants in creating situations that are potentially conducive to infant social learning. Eleven gorilla mother-infant dyads were focally observed in weekly 1-hr sessions for 12 months. Spatial relationships were affected by age as well as by ambient temperature. Although the youngest infant was encouraged by its mother to walk and climb, mothers showed little or no encouragement in other contexts. In contrast, infants were quite interested in their mothers' activities, on some occasions repeated their mother's behavior, and actively encouraged their mothers to share food, play, or follow them. These findings suggest that gorilla infants are more active than their mothers in creating situations that are potentially conducive to the acquisition of knowledge or skills.     

Avoidance of heat by rats: Effects of thermal context on rapidity of extinction

Rats were trained to avoid radiant heat in a one-way, jump-up apparatus. The animals that could avoid heat responded more frequently and more rapidly than did yoked controls that received heat, but for whom no avoidance contingency was deliberately arranged. Control animals trained with light, rather than heat, did not learn to avoid. Using this jump-up avoidance, rats were trained to avoid heat in a room maintained at 27°C. They were then given a series of extinction trials, with no heat presentations, with the temperature maintained at either 27 or 7°C. Placing the rats in a cold environment facilitated extinction of heat avoidance behavior, but only in animals that had previously experienced heat while they were in the cold. Prior heat experience administered in a warm, rather than cold, context was not sufficient to potentiate the effect of ambient temperature on avoidance extinction. Implications of these results for theories of avoidance learning are discussed.     

Gender differences in acute and chronic stress in Wistar Kyoto (WKY) rats

While females are considered more susceptible to depressive behavior, this assertion is not strongly supported by the experimental literature. Since stress contributes to depressive behavior, male and female Wistar Kyoto (WKY) rats were exposed to either one session (acute stress) or 5 sessions (chronic stress) of restraint plus cold in order to study depressive behavior in male and female rats. After their respective treatment exposure, rats were tested in the open field test (OFT) and for retention of a passive-avoidance (P-A) task. One stress session resulted in significant immobility in the OFT for males, whereas 5 sessions were required to produce similar immobility in female rats. Acute stress interfered with the retention of the P-A response for males, while both acute and chronic stress produced poor P-A responses in female rats. Food consumption decresed, progressively, as a function of stress sessions, in female rats, whereas feeding in males returned to control levels after five stress days. Both acute and chronic stress exacerbated the stress ulcer response in male rats, but not in female rats. Chronic, but not acute, stress resulted in an increase in serotonin transporter mRNA levels in the dorsal raphe nucleus of both male and, female rats. The general consensus from these data suggested that female rats were more vulnerable to chronic stress and consequently supported the notion that females may be more susceptible to stress induced behavioral depression.     

Early learning as ontogenetic adaptation for ingestion by rats

Ontogenetic adaptation is an “ecological” concept in which mammalian maturation is seen as a coordinated sequence of specializations (stages) that enables the infant to survive within a sequence of distinct niches created by the parent(s) and the rest of the environment. Natural selection is presumed to operate at each point in development. The development of ingestive behavior in the rat pup as a series of ontogenetic adaptations enabling the infant while in the nursing niche to obtain and utilize mother's milk and progress gradually into the feeding niche in which a variety of solid foods must either be obtained or avoided is discussed. Data to show that learning is an integral part of these ontogenetic adaptations for ingestion are reviewed and interpreted. Preweanling rats that are capable of learning and remembering toxiphobic food aversions do not display an aversion to a flavor conditioned stimulus (CS) paired with illness if the CS is presented during suckling. In contrast, 20-day-old pups (weanlings) trained identically do show conditioned taste aversions under these conditions. A perspective of ontogenetic adaptations to this phenomenon of “blockade of toxiphobia by suckling” and its dissolution at weaning is applied. The generality of the blockade phenomenon and its mechanisms are explored, and it is shown that feeding experience regulates the stage-appropriate learning strategies used by the pups.     

The disturbed caregiving system: Relations among childhood trauma,maternal caregiving,and infant affect and attachment

The interrelations among maternal childhood experiences of physical or sexual abuse, adult trauma-related symptoms, adult caregiving behavior, and infant affect and attachment were investigated among 45 low-income mothers and their 18-month-old infants. A history of physical abuse was associated with increased hostile-intrusive behavior toward the infant, increased infant negative affect, and a decreased tendency to report trauma-related symptoms. A history of sexual abuse was associated with decreased involvement with the infant, more restricted maternal affect, and more active reporting of trauma-related symptoms. Infants of mothers who had experienced childhood violence or abuse were not more likely to display insecure attachment strategies than infants of mothers who had not experienced trauma. However, the form of insecure behavior was significantly different. Insecure infants of violence-exposed mothers displayed predominantly disorganized strategies, whereas insecure infants of mothers with benign childhoods or neglect only displayed predominantly avoidant strategies. Results are discussed in relation to Main and Hesse's (1990) concept of frightened or frightening behavior and to current literature on psychological sequelae of trauma.