The human amygdala and the induction and experience of fear

Although clinical observations suggest that humans with amygdala damage have abnormal fear reactions and a reduced experience of fear, these impressions have not been systematically investigated. To address this gap, we conducted a new study in a rare human patient, SM, who has focal bilateral amygdala lesions. To provoke fear in SM, we exposed her to live snakes and spiders, took her on a tour of a haunted house, and showed her emotionally evocative films. On no occasion did SM exhibit fear, and she never endorsed feeling more than minimal levels of fear. Likewise, across a large battery of self-report questionnaires, 3 months of real-life experience sampling, and a life history replete with traumatic events, SM repeatedly demonstrated an absence of overt fear manifestations and an overall impoverished experience of fear. Despite her lack of fear, SM is able to exhibit other basic emotions and experience the respective feelings. The findings support the conclusion that the human amygdala plays a pivotal role in triggering a state of fear and that the absence of such a state precludes the experience of fear itself.     

The Fragrant Power of Collective Fear

Fear is a well-characterized biological response to threatening or stressful situations in humans and other social animals. Importantly, fearful stimuli in the natural environment are likely to be encountered concurrently by a group of animals. The modulation of fear acquisition and fear memory by a group as opposed to an individual experience, however, remains largely unknown. Here, we demonstrate a robust reduction in fear memory to an aversive event undertaken in a group despite similar fear learning between individually- and group-conditioned rats. This reduction persists outside the group confines, appears to be a direct outcome of group cognizance and is counteracted by loss of olfactory signaling among the group members. These results show that a group experience of fear can be protective and suggest that distinct neural pathways from those classically studied in individuals modulate collective fear memories.     

Knowing no fear

People with brain injuries involving the amygdala are often poor at recognizing facial expressions of fear, but the extent to which this impairment compromises other signals of the emotion of fear has not been clearly established. We investigated N.M., a person with bilateral amygdala damage and a left thalamic lesion, who was impaired at recognizing fear from facial expressions. N.M. showed an equivalent deficit affecting fear recognition from body postures and emotional sounds. His deficit of fear recognition was not linked to evidence of any problem in recognizing anger (a common feature in other reports), but for his everyday experience of emotion N.M. reported reduced anger and fear compared with neurologically normal controls. These findings show a specific deficit compromising the recognition of the emotion of fear from a wide range of social signals, and suggest a possible relationship of this type of impairment with alterations of emotional experience.     

The scent of fear

In this study we tried to find out if fear can be detected from human body odours. Female subjects wore under-arm axillary pads while watching a terrifying film. Saliva cortisol samples were taken before and after the film presentation as a hormonal measure for the fear response. The fear experience itself was measured by Spielberger's State-Trait Anxiety Inventory. A "neutral" film, shown one day after the "fear" film, was used as a control in a repeated measures design. In part two of the experiment, the axillary pads were presented to female subjects in a triple forced choice test. Results show that subjects were able to discriminate between fear and non-fear axillary pads, suggesting that women are indeed able to detect "the scent of fear". A direct correlation between induced fear, changes in cortisol levels and smell ratings could not be established. Thus cortisol levels are probably not the inducer of the scent of fear and a hypothetical fear pheromone could have other origins.     

运用虚拟现实暴露疗法治疗飞行恐惧症的研究述评

虚拟现实暴露疗法是治疗飞行恐惧症的新方法。与传统的暴露疗法相比,虚拟现实暴露疗法集合了实体暴露疗法和想象暴露疗法的优点。避免了二者的不足,具有灵活、高效、安全、可重复和易于操控的特点。研究者们利用数据头盔、双通道立体声耳机、追踪设备、感应器等设备给飞行恐惧症患者呈现实时的计算机动画、双通道立体声和触觉刺激,使之沉浸在虚拟的飞行情景中,从而激发出患者的恐惧情绪。在虚拟现实暴露治疗的过程中,治疗师根据患者的情况使之逐步暴露在不同等级的刺激性情景中,经反复练习逐渐耐受并适应这些情景,最终克服不合理的恐惧。近10年的大量研究表明:虚拟现实暴露疗法能有效地治愈飞行恐惧症,在临床上具有良好的应用前景。今后的研究将进一步比较虚拟现实暴露疗法与其他治疗方法的疗效,并开发出成本更低、临场感更好的虚拟现实设备以扩展虚拟现实暴露疗法在飞行恐惧症治疗中的应用。     

Worrying affects associative fear learning: a startle fear conditioning study

A valuable experimental model for the pathogenesis of anxiety disorders is that they originate from a learned association between an intrinsically non-aversive event (Conditioned Stimulus, CS) and an anticipated disaster (Unconditioned Stimulus, UCS). Most anxiety disorders, however, do not evolve from a traumatic experience. Insights from neuroscience show that memory can be modified post-learning, which may elucidate how pathological fear can develop after relatively mild aversive events. Worrying--a process frequently observed in anxiety disorders--is a potential candidate to strengthen the formation of fear memory after learning. Here we tested in a discriminative fear conditioning procedure whether worry strengthens associative fear memory. Participants were randomly assigned to either a Worry (n = 23) or Control condition (n = 25). After fear acquisition, the participants in the Worry condition processed six worrisome questions regarding the personal aversive consequences of an electric stimulus (UCS), whereas the Control condition received difficult but neutral questions. Subsequently, extinction, reinstatement and re-extinction of fear were tested. Conditioned responding was measured by fear-potentiated startle (FPS), skin conductance (SCR) and UCS expectancy ratings. Our main results demonstrate that worrying resulted in increased fear responses (FPS) to both the feared stimulus (CS(+)) and the originally safe stimulus (CS(-)), whereas FPS remained unchanged in the Control condition. In addition, worrying impaired both extinction and re-extinction learning of UCS expectancy. The implication of our findings is that they show how worry may contribute to the development of anxiety disorders by affecting associative fear learning.     

On the Validity of the Autobiographical Emotional Memory Task for Emotion Induction

The Autobiographical Emotional Memory Task (AEMT), which involves recalling and writing about intense emotional experiences, is a widely used method to experimentally induce emotions. The validity of this method depends upon the extent to which it can induce specific desired emotions (intended emotions), while not inducing any other (incidental) emotions at different levels across one (or more) conditions. A review of recent studies that used this method indicated that most studies exclusively monitor post-writing ratings of the intended emotions, without assessing the possibility that the method may have differentially induced other incidental emotions as well. We investigated the extent of this issue by collecting both pre- and post-writing ratings of incidental emotions in addition to the intended emotions. Using methods largely adapted from previous studies, participants were assigned to write about a profound experience of anger or fear (Experiment 1) or happiness or sadness (Experiment 2). In line with previous research, results indicated that intended emotions (anger and fear) were successfully induced in the respective conditions in Experiment 1. However, disgust and sadness were also induced while writing about an angry experience compared to a fearful experience. Similarly, although happiness and sadness were induced in the appropriate conditions, Experiment 2 indicated that writing about a sad experience also induced disgust, fear, and anger, compared to writing about a happy experience. Possible resolutions to avoid the limitations of the AEMT to induce specific discrete emotions are discussed.     

Proximate causes and consequences of intergenerational influences of salient sensory experience

Salient sensory environments experienced by a parental generation can exert intergenerational influences on offspring. While these data provide an exciting new perspective on biological inheritance, questions remain about causes and consequences of intergenerational influences of salient sensory experience. We previously showed that exposing male mice to a salient olfactory experience, like olfactory fear conditioning, resulted in offspring demonstrating a sensitivity to the odor used to condition the paternal generation and possessing enhanced neuroanatomical representation for that odor. In this study, we first injected RNA extracted from sperm of male mice that underwent olfactory fear conditioning into naïve single‐cell zygotes and found that adults that developed from these embryos had increased sensitivity and enhanced neuroanatomical representation for the odor (Odor A) with which the paternal male had been conditioned. Next, we found that female, but not male offspring sired by males conditioned with Odor A show enhanced consolidation of a weak single‐trial Odor A + shock fear conditioning protocol. Our data provide evidence that RNA found in the paternal germline after exposure to salient sensory experiences can contribute to intergenerational influences of such experiences, and that such intergenerational influences confer an element of adaptation to the offspring. In so doing, our study of intergenerational influences of parental sensory experience adds to existing literature on intergenerational influences of parental exposures to stress and dietary manipulations and suggests that some causes (sperm RNA) and consequences (behavioral flexibility) of intergenerational influences of parental experiences may be conserved across a variety of parental experiences.     

What do fish make of mirror images?

Fish act aggressively towards their mirror image suggesting that they consider it another individual, whereas in some mammals behavioural response to mirrors may be an evidence of self-recognition. Since fish cannot self-recognize, we asked whether they could distinguish between fighting a mirror image and fighting a real fish. We compared molecular, physiological and behavioural responses in each condition and found large differences in brain gene expression levels. Although neither levels of aggressive behaviour nor circulating androgens differed between these conditions, males fighting a mirror image had higher immediate early gene (IEG) expression in brain areas homologous to the amygdala and hippocampus than controls. Since amygdalar responses are associated with fear and fear conditioning in other species, higher levels of brain activation when fighting a mirror suggest fish experience fear in response to fights with a mirror image. Clearly, the fish recognize something unusual about the mirror image and the differential brain response may reflect a cognitive distinction.     

Resting Heart Rate Variability and the Effects of Biofeedback Intervention in Women with Low-Risk Pregnancy and Prenatal Childbirth Fear

Anxiety about labor in women at the end of pregnancy sometimes reaches levels that are clinically concerning. We investigated whether low-risk pregnant women with childbirth fear during the last trimester demonstrate specific findings with regard to resting heart rate variability (HRV) and examined whether HRV biofeedback can reduce this fear and alter resting HRV. We measured the levels of childbirth fear (Wijma delivery expectancy/experience questionnaire, W-DEQ) and resting HRV indexes in 97 low-risk pregnant women in their 32nd–34th week of gestation and advised women with W-DEQ scores of ≥?66 (n?=?40) to practice HRV biofeedback (StressEraser) at home. We then reassessed these measures 3–4 weeks later in the 36th–37th week of gestation regardless of whether the women practiced the method. We found that childbirth fear had no significant effect on resting HRV indexes when the W-DEQ cutoff was conventionally set at ≥?66. However, women with W-DEQ scores of ≥?90 (n?=?5) had a significantly lower high-frequency power than their counterparts (p?=?0.028). The W-DEQ scores reduced significantly in women who performed HRV biofeedback (n?=?18, p?<?0.001), but there was no change in those who did not perform the method (n?=?20). These findings suggested that very high W-DEQ scores (≥?90), but not the conventional criteria (W-DEQ score?≥?66), of the fear of childbirth were associated with low parasympathetic activity among low-risk pregnant women and that HRV biofeedback intervention can effectively decrease the fear of childbirth in these women.     

Neuroticism modifies psychophysiological responses to fearful films

Background

Neuroticism is a personality component frequently found in anxious and depressive psychiatric disorders. The influence of neuroticism on negative emotions could be due to its action on stimuli related to fear and sadness, but this remains debated. Our goal was thus to better understand the impact of neuroticism through verbal and physiological assessment in response to stimuli inducing fear and sadness as compared to another negative emotion (disgust).

Methods

Fifteen low neurotic and 18 high neurotic subjects were assessed on an emotional attending task by using film excerpts inducing fear, disgust, and sadness. We recorded skin conductance response (SCR) and corrugator muscle activity (frowning) as indices of emotional expression.

Results

SCR was larger in high neurotic subjects than in low neurotics for fear relative to sadness and disgust. Moreover, corrugator activity and SCR were larger in high than in low neurotic subjects when fear was induced.

Conclusion

After decades of evidence that individuals higher in neuroticism experience more intense emotional reactions to even minor stressors, our results indicate that they show greater SCR and expressive reactivity specifically to stimuli evoking fear rather than to those inducing sadness or disgust. Fear processing seems mainly under the influence of neuroticism. This modulation of autonomic activity by neurotics in response to threat/fear may explain their increased vulnerability to anxious psychopathologies such as PTSD (post traumatic stress disorder).     

Amnesia,Anesthesia, and Warranted Fear

Is a painful experience less bad for you if you will not remember it? Do you have less reason to fear it? These questions bear on how we think about medical procedures and surgeries that use an anesthesia regimen that leaves patients conscious – and potentially in pain – but results in complete ‘drug‐induced amnesia’ after the fact. I argue that drug‐induced amnesia does not render a painful medical procedure a less fitting object of fear, and thus the prospect of amnesia does not give patients a reason not to fear it. I expose three mistakes in reasoning that might explain our tendency to view pain or discomfort as less fearful in virtue of expected amnesia: a mistaken view of personal identity; a mistaken view of the target of anticipation; and a mistaken method of incorporating past evidence into calculations about future experiences. Ultimately my argument has implications for whether particular procedures are justified and how medical professionals should speak with anxious patients about the prospect of drug‐induced amnesia.     

Effects of a Post-Shock Injection of the Kappa Opioid Receptor Antagonist Norbinaltorphimine (norBNI) on Fear and Anxiety in Rats

Exposure of rats to footshocks leads to an enduring behavioral state involving generalized fear responses and avoidance. Recent evidence suggests that the expression of negative emotional behaviors produced by a stressor is in part mediated by dynorphin and its main receptor, the kappa opioid receptor (KOR). The purpose of this study was to determine if a subcutaneous injection of the long-acting KOR antagonist norbinaltorphimine (norBNI; 15.0 and 30.0 mg/kg) given 2 days after an acute exposure of rats to footshooks (5×2 s episodes of 1.5 mA delivered over 5 min) attenuates the expression of lasting fear and anxiety. We report that exposure of rats to acute footshock produced long-lasting (>4 weeks) fear (freezing) and anxiety (avoidance of an open area in the defensive withdrawal test). The 30 mg dose of norBNI attenuated the fear expressed when shock rats were placed in the shock context at Day 9 but not Day 27 post-shock. The same dose of norBNI had no effect on the expression of generalized fear produced when shock rats were placed in a novel chamber at Days 8 and 24. In contrast, the 30 mg dose of norBNI produced consistent anxiolytic effects in shock and nonshock rats. First, the 30 mg dose was found to decrease the latency to enter the open field in the defensive withdrawal test done 30 days after the shock exposure. Second, the same high dose also had anxiolytic effects in both nonshock and shock rats as evidence by a decrease in the mean time spent in the withdrawal box. The present study shows that systemic injection of the KOR antagonist norBNI had mixed effect on fear. In contrast, norBNI had an anxiolytic effect which included the attenuation of the enhanced avoidance of a novel area produced by a prior shock experience.     

Fear and exploration in European starlings (Sturnus vulgaris): a comparison of hand-reared and wild-caught birds

The revision of EU legislation will ban the use of wild-caught animals in scientific procedures. This change is partially predicated on the assumption that captive-rearing produces animals with reduced fearfulness. Previously, we have shown that hand-reared starlings (Sturnus vulgaris) indeed exhibit reduced fear of humans compared to wild-caught conspecifics. Here, we asked whether this reduction in fear in hand-reared birds is limited to fear of humans or extends more generally to fear of novel environments and novel objects. Comparing 6-8 month old birds hand-reared in the lab with age-matched birds caught from the wild as fledged juveniles a minimum of 1 month previously, we examined the birds' initial reactions in a novel environment (a small cage) and found that wild-caught starlings were faster to initiate movement compared to the hand-reared birds. We interpret this difference as evidence for greater escape motivation in the wild-caught birds. In contrast, we found no differences between hand-reared and wild-caught birds when tested in novel object tests assumed to measure neophobia and exploratory behaviour. Moreover, we found no correlations between individual bird's responses in the different tests, supporting the idea that these measure different traits (e.g. fear and exploration). In summary, our data show that developmental origin affects one measure of response to novelty in young starlings, indicative of a difference in either fear or coping style in a stressful situation. Our data contribute to a growing literature demonstrating effects of early-life experience on later behaviour in a range of species. However, since we did not find consistent evidence for reduced fearfulness in hand-reared birds, we remain agnostic about the welfare benefits of hand-rearing as a method for sourcing wild birds for behavioural and physiological research.     

Social transmission of fear in rats: the role of 22-kHz ultrasonic distress vocalization

Background

Social alarm calls alert animals to potential danger and thereby promote group survival. Adult laboratory rats in distress emit 22-kHz ultrasonic vocalization (USV) calls, but the question of whether these USV calls directly elicit defensive behavior in conspecifics is unresolved.

Methodology/Principal Findings

The present study investigated, in pair-housed male rats, whether and how the conditioned fear-induced 22-kHz USVs emitted by the ‘sender’ animal affect the behavior of its partner, the ‘receiver’ animal, when both are placed together in a novel chamber. The sender rats’ conditioned fear responses evoked significant freezing (an overt evidence of fear) in receiver rats that had previously experienced an aversive event but not in naïve receiver rats. Permanent lesions and reversible inactivations of the medial geniculate nucleus (MGN) of the thalamus effectively blocked the receivers’ freeezing response to the senders'' conditioned fear responses, and this occurred in absence of lesions/inactivations impeding the receiver animals'' ability to freeze and emit 22-kHz USVs to the aversive event per se.

Conclusions/Significance

These results—that prior experience of fear and intact auditory system are required for receiver rats to respond to their conspecifics'' conditioned fear responses—indicate that the 22-kHz USV is the main factor for social transmission of fear and that learning plays a crucial role in the development of social signaling of danger by USVs.     

Behavioral alterations induced by repeated testing in C57BL/6J and 129S2/Sv mice: implications for phenotyping screens

The C57BL/6JOlaHsd and 129S2/SvHsd mice were tested in a battery designed for behavioral phenotyping of genetically modified mice. The study was performed in order to reveal the effect of training history on the behavior by comparison with the experimentally naïve mice in the same tests. Significant strain differences were obtained in all experiments. Previous handling and testing reduced exploratory activity and emotionality significantly in the mice. The coordination ability was better and nociceptive sensitivity was increased in the trained mice. The contextual fear was reduced whereas the cued fear was enhanced in the experienced mice. The training history did not alter initial learning in the water maze. However, after reversal learning the naïve mice displayed significant preference for both old and new platform locations, whereas the battery animals did not exhibit preference to the old location. The experienced mice appeared to be less active in the forced swimming test and exhibited decreased conditioned taste aversion. The influence of test history was strain-dependent in certain cases. Therefore, the experience has substantial consequences on the behavior, mainly by reducing exploratory activity, and the previous experience of the animals has always to be considered in the analysis of genetically modified mice.     

The relationship of fearfulness to,and the effects of,sex, age and experience on exploration and activity in dogs

The correlations between measures of activity in different situations, including inhibitory training, were positive but low. Activity in non-stressful situations was independent of fearfulness. There appears to be individual variation between dogs which determines whether a dog responds to fear by increasing or decreasing activity. Fearfulness was correlated with high visual and auditory exploration. General fearfulness was uncorrelated with olfactory exploration, but lack of experience in crowded, noisy places increased both olfactory exploration and fear of certain objects likely to be encountered in such places, and so caused a correlation between these two traits. Dogs which were reared in a home with another dog were less distracted by other dogs. Between 6 and 12 months, the dogs declined in activity and unwanted exploration. Females showed a higher level of activity during inhibitory training and a higher level of olfactory exploration than males.     

The Role of Gender in Public Perception of Whether Animals Can Experience Grief and Other Emotions

Gender plays a significant role in influencing people's attitudes toward animals, however, little is known about how it influences their attribution of emotions to animals. To investigate the role that gender plays in public attitudes toward animals' experience of emotions and beliefs about whether animals can grieve, a face-to-face survey of 1,000 members of the general public was carried out in Brisbane, Australia. Potential respondents were asked to complete a 10-min “social attitudinal” survey. Males were significantly less likely than females to believe that animals experience complex emotions, including depression (p < 0.05), anxiety (p < 0.05), love (p < 0.01), and grief (p < 0.05), but did not differ in regard to basic emotions including distress, fear, happiness, anger, sadness, and fear. Males were also less likely to believe that animals show some behavioral (eating p < 0.05; vocalizing p < 0.01) changes when they experience grief (p < 0.05) and that animals grieve as a result of separation from a conspecific (p < 0.005). These results demonstrate a greater skepticism in males, compared with females, regarding the attribution of emotions to animals.     

Reproductive Experience and the Response of Female Sprague�CDawley Rats to Fear and Stress

The present work examines the relationship between reproductive experience (comprising breeding, parturition, and lactation) and the behavioral and hormonal processes of fear and stress in the female laboratory rat. Previous research has indicated that reproductive experience functions to decrease the female''s stress response in potentially harmful environments, thereby providing her with numerous survival benefits, including decreased fearfulness, increased aggression, and refined hunting skills. This study was designed to determine how nulliparous (no reproductive experience), primiparous (1 reproductive experience) and multiparous (at least 2 reproductive experiences) rats respond to a Pavlovian paradigm of learned fear, involving the pairing of a neutral stimulus (conditioned stimulus) with an aversive stimulus (unconditioned stimulus). We report evidence that reproductive experience is linked with fear-response and anxiety-like behaviors. Our findings indicate that reproductive experience has an additive effect: primiparous mothers showed a different response to the paradigm of conditioned fear not only compared with those of nulliparous rats as well as multiparous mothers. Assessing the complex interconnections among the behavioral and physiologic measures recorded in this study, multidimensional scaling confirmed a clear separation among the 3 groups of rats in terms of the behavioral and physiologic responses to the experimental paradigm, supporting the conclusion that reproductive experience influences the maternal mind.Stress, fear, and lack of adequate stimuli can constitute a serious problem for laboratory animals. Although several studies have investigated various social and environmental changes to improve the health of laboratory animals, the literature on husbandry regimen and reproductive experience is scarce.^{3,23,44,56,58} Pregnancy and lactation represent the quintessence of change in mammals.^13,38 Reproduction entails high physiologic costs, especially in small mammals like rodents, including increased energy and nutrient demands, making the connection between husbandry and health in laboratory rats even more compelling.⁴⁹ Extensive neuroendocrine and behavioral modifications ensure mothers the flexibility to meet their own survival needs with the survival of their offspring in most environmental contingencies.^30,46 The long-term effects of these changes on the somatic and psychologic development of infants are well-known and pervasive in most mammals: from immediate infant survival to the ability to cope with stress during adulthood.^5,7,22,26,43 Several studies have indicated that the long-term consequences on mothers themselves are as compelling. Although some authors have found a significant decrease in cell proliferation in the dentate gyrus of the hippocampus in primiparous and multiparous rats during the postpartum period, associated with temporary impaired learning skills,¹⁵ others have found that motherhood can improve spatial cognition, learning and memory,^9,27,33,42 through mechanisms based on increased glucocorticoid production.^31,41 The combination of improved behavioral performances and increased physiologic stress in mothers is hardly surprising considering that the sequence of modifications during pregnancy involves, as a cascade of events, the whole body and shapes the inherently plastic central nervous system to cope with the extra challenges of providing for offspring. At the pinnacle of its fruition, the maternal brain is responsible for a complex set of behaviors that mold mothers in every aspect of their life.^28,29 In this scenario, we expect that empirical examinations of laboratory female rats with differential reproductive experience would yield significant differences in both the fear and stress response of maternal and virgin rats. Because stress and fear can impair the health of research animals and, if not controlled for, confound results obtained in experimental data, it is important to evaluate how reproductive experience can modify both stress and fear responses. Previous studies have indicated that, when confronted with a stressful stimulus, maternal rats display fewer stress-related behaviors than do nonmaternal rats.^32,57One common method of examining the animal''s reaction to a threatening environment is to use a Pavlovian model of learned fear. The neural circuitry of learned fear, involving the association of a conditioned stimulus or context with an unconditioned stimulus, is of particular interest because learned fear processes involve multiple cognitive functions including predicting, representing, and defining relationships between events.⁴⁵ The literature discussing the neural correlates of learned fear is vast and, further, agrees that the amygdala is the central brain structure responsible for learned fear. In fact, bilateral damage to the amygdala seriously impairs Pavlovian fear conditioning.^8,53 Studies conducted in developing rats revealed that different nuclei of the amygdala process sensory information of different modalities, mediate unconditioned freezing behavior, and may be involved in developmental changes in the fear response in young rats.¹⁴ Research elucidating a relationship or lack thereof between reproductive experience and changes in fear response is limited presently.^19,55 Examinations of unconditioned fear and maternal experience have suggested that an attenuated stress response and an overall decrease in fearfulness provides numerous survival benefits, such as enhanced and increased hunting and gathering skills, exploration, social awareness, and aggression, to the female rat.^21,37,50,51 Because survivability is dependent upon the prediction and appropriate response to threatening stimuli, this research paradigm can provide pertinent information about the animal''s fitness, thus providing critical information on both the health of animals and the quality of experimental data.Pregnancy, lactation, and the complex behavioral repertoire comprising maternal care constitute an expensive metabolic and genetic investment that is pivotal to species survival.^11,52 Alterations of the female brain due to occurrences of several cycles of pup exposure are reflected in many aspects of maternal life, including fear responses, activation of the hypothalamic–pituitary–adrenal axis, and anxiety.¹⁰ In the present work, we assessed whether reproductive experience plays a specific role on fear response and how this response activates the hypothalamic–pituitary–adrenal axis and interacts with anxiety-related behaviors in rats. We also assessed whether these effects are additive, that is, whether multiparous mothers (2 or more pregnancies) have a different fear response than do primiparous mothers (only 1 pregnancy). On the basis of information provided by previous studies, we hypothesized that during the retention–testing trials of the conditioning model, maternal subjects (primiparous and multiparous groups) would express fewer fear-related (freezing) behaviors than would nonmaternal subjects (nulliparous group). We further hypothesized that the maternal groups would express anxiety-related behaviors less frequently than would the nonmaternal group during the retention–testing trials. In addition, we speculated that the nulliparous group would exhibit significantly higher activation of the hypothalamic–pituitary–adrenal axis than would the reproductive groups (primiparous and multiparous), as measured by corticosterone concentrations after the fear-conditioning training trials.     

Pain perception, aversion and fear in fish

There is now compelling evidence that teleost fish possess similar nociceptive processing systems to those found in terrestrial vertebrates. Noxious stimulation of these nociceptors--specialised pain receptors -in the skin around the snout of fish generates neural activity that can be electrophysiologically recorded, and induces a number of behavioural and physiological changes. To determine whether changes in behaviour are more than simple responses to the noxious stimulation it is necessary to demonstrate that higher order cognitive processes such as mental state or 'affective state' are involved. However, quantifying the 'motivational affected state' of an animal--a concept encompassing not just pain but also fear, hunger, thirst and pleasure - is difficult owing to its subjectivity. Recent empirical work is beginning to test these concepts in fish, and we review a number of these studies and suggest how these general methodologies could be used to further our understanding of fish cognition and the capacity for fish to experience mental states such as fear or suffering.