Literature Review

Post-traumatic stress disorder: Evolutionary perspectives

Article· Literature ReviewinAustralian and New Zealand Journal of Psychiatry 43(11):1038-48 · November 2009with 907 Reads
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Abstract
Fear is the key emotion of post-traumatic stress disorder (PTSD). Fear's evolved function is motivating survival via defensive behaviours. Defensive behaviours have been highly conserved throughout mammalian species; hence much may be learned from ethology. Predation pressure drove the early evolution of defences, laying foundations in the more ancient brain structures. Conspecific (same species) pressure has been a more recent evolutionary influence, but along with environmental threats it has dominated PTSD research. Anti-predator responses involve both avoiding a predator's sensory field and avoiding detection if within it, as well as escape behaviours. More effective avoidance results in less need for escape behaviours, suggesting that avoidance is biologically distinct from flight. Recognizing the predation, environmental and conspecific origins of defence may result in clearer definition of PTSD phenomena. Defence can also be viewed in the stages of no threat, potential threat, encounter and circa strike. Specific defences are used sequentially and according to contexts, loosely in the order: avoidance, attentive immobility, withdrawal, aggressive defence, appeasement and tonic immobility. The DSM-IV criteria and PTSD research show substantial congruence with the model proposed: that PTSD is a disorder of heightened defence involving six key defences used in conjunction with vigilance and risk assessment according to contexts. Human research is reviewed in this respect with reference to laboratory and wild animal observations providing new insights. Understanding individual perceptual issues (e.g. predictability and controllability) relevant to these phenomena, combined with defence strategy recalibration and neuronal plasticity research goes some way to explaining why some traumatized individuals develop PTSD when others do not.
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  • Article
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  • Article
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Literature Review
  • Article
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    One of the most important and obvious forces shaping organismal traits is predation. Prey have evolved diverse means of enhancing the probability of survival in the face of predation, and these means fall into two classes of antipredator strategies: (1) avoidance of predatory encounters, and (2) escaping after encountering a predator. A range of antipredator defenses—including behavioral, morphological, physiological, and chemical defenses—serve to either reduce the probability of detection by a predator or enhance the probability of surviving after detection by a predator. However, the recognition that reproductive strategies (e.g. offspring number, reproductive lifespan) are typically strongly influenced by mortality regimes induced by predators, highlights that most but not all “antipredator traits” fall into one of these two categories—that is, some life history traits influence only fecundity, not survival. Life history evolution has not traditionally been included in reviews of antipredator adaptations, however this chapter reveals that the conceptual link between life histories and predation broadens and refines our understanding of predation’s role in phenotype evolution.
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    Introduction. Chance, A Systems Synthesis of Mentality. Emory, Social Geometry & Cohesion in Three Primate Species. Pitcairn, Social Attention and Social Awareness. Power, The Cohesive Foragers: Human and Chimpanzee. de Waal, The Reconciled Hierarchy. Itani, The Origin of Human Equality. Price, Alternative Channels for Negotiating the Definitions of Social Relationships. Gardner, Psychiatric Syndromes as Infrastructure for Intraspecific Communication. Scott-Lewis, The Therapeutic Use of an Ethogram in a Drug Addiction Unit: Social Referent Allegiances. Montagner et al, Social Interactions of Young Children with Peers and their Modification in Relation to Environmental Factors. Barner-Barry, The Structure of Politically Relevant Behaviours in Pre-School Peer Groups. Masters, Nice Guys DON'T Finish Last: Aggressive & Appeasement Gestures in Media Images of Politicians. Kemper, The Two Dimensions of Sociality. Wedgewood-Oppenheim, Organizational Culture and the Agonic, Hedonic Bimodality. Glossary. Indices.
  • Article
    Abstract The pre-eminent model of flight initiation distance assumes that the function relating predation risk to distance between predator and prey is constant. However, the risk–distance function can change dramatically during approaches by predators. Changes in predator behavior during approach and in availability of benefits (e.g. food or potential mates) may alter risks and/or costs during encounters. Thus, prey should be able to respond appropriately to changes in cues to risk, such as predator approach speed. Under the assumption that prey assess risk in real time, it was predicted that flight initiation distance (distance between predator and prey when escape begins) decreases when approach speed increases and increases when approach speed decreases during an encounter. Effects of single, abrupt changes from slower to faster approach or the reverse were studied in a lizard, Anolis lineatopus. Flight initiation distances were determined solely by final approach speed, being nearly identical for: (1) continuously fast approaches and approaches initially at the slower and finally at the faster speed and (2) for continuously slower approaches and approaches initially at faster and finally at slower speed. Escape should be adjusted to match changes in risk and cost caused by changes in predator behavior, ability to escape, and costs of escape as attacks unfold. A recent model by Broom and Ruxton [Behavioural Ecology (2004) vol. 16, pp. 534—540] predicts that cryptic prey should stay motionless until detected, then flee immediately. Our results suggest that current escape models can be applied to prey escape strategies when cues to risk change, by assuming that prey base decisions on the current relationship between risk and distance. Empirical studies are needed to test predictions concerning continuous risk assessment.
  • Article
    Preclinical animal models are utilized in the study of unconditioned states related to fear and anxiety. They are used to screen novel pharmaceuticals, study behavioral phenomena, and understand underlying etiology. In this chapter, we will present a brief overview of the most prevalently used models, discuss their various applications, and state their main behavioral indices. We will conclude by discussing the importance of factors associated with the environment and the chosen experimental subjects to appropriately model preclinical states associated with fear and anxiety.
  • Article
    Analysis of the pattern of defensive behaviours in semi-natural situations suggests a long-duration process in which high level freezing/movement arrest gradually gives way to active risk assessment activities, terminating with a gradual return to nondefensive behaviours. Risk assessment is conceptualized as the key feature in this process, with the information obtained by these oriented scanning and exploratory activities providing feedback to reduce the subject’s initial high level of defensiveness. Risk assessment measures derived from this analysis are selectively responsive to classic anxiolytics. Examination of a range of commonly used measures of anxiolytic action suggest that many of these contain clear elements of the risk assessment process. Furthermore, variation in the results obtained in these tests might be profitably analyzed in terms of some of the features of risk assessment and other aspects of the defense pattern seen to partial or potential threat stimuli.
  • Article
    Overt signs of victim resistance during rape are critical issues in the handling of and recovery from rape/sexual assault. However, a substantial number of victims do not resist the attacker in any way. Tonic immobility (TI), a well-known involuntary, reflexive response to fear-inducing stimuli, may aid in explaining the paralysis and “freezing” of many rape victims. In the present study, rape survivors were classified as immobile, intermediate, or mobile, based on a self-report measure. The immobile group manifested significantly more of the specific features associated with tonic immobility. Thirty-seven percent of the sample clearly demonstrated immobility during the attack. Various postrape behaviors and attitudes were found to be associated with the incidence of the immobility response.
  • Article
    BACKGROUND: Previous studies suggested the importance of peritraumatic reactions as predictors of PSTD symptoms severity. Despite mounting evidence that tonic immobility occurs under intense life threats its role as predictor of PTSD severity remains by and large understudied. The objective of this study was to investigate the role of peritraumatic reactions (tonic immobility, panic and dissociation) as predictors of PTSD symptoms severity. METHODS: Participants were 32 victims of urban violence with PTSD diagnosed through the SCID-I. In order to evaluate PTSD symptoms at baseline, we used the Post-Traumatic Stress Disorder Checklist-Civilian Version. To assess peritraumatic reactions we employed the Physical Reactions Scale, the Peritraumatic Dissociative Experiences Questionnaire and Tonic Immobility questions. As confounding variables, we considered negative affect (measured by the Positive and Negative Affect Schedule-Trait Version), sex and time elapsed since trauma. RESULTS: Tonic immobility was the only predictor of PTSD symptoms severity that kept the statistical significance after controlling for potential confounders. LIMITATIONS: This study was based on a relatively small sample recruited in a tertiary clinic, a fact that may limit the generalizability of its findings. The retrospective design may have predisposed to recall bias. CONCLUSIONS: Our study provides good reason to conduct more research on tonic immobility in PTSD with other samples and with different time frames in an attempt to replicate these stimulating results.
  • Article
    Full-text available
    the predatory imminence continuum / pre-encounter defensive behavior / post-encounter defensive behavior / circa-strike defensive behavior / recuperation and the return to the preferred activity pattern / temporal and spatial aspects of predatory imminence (PsycINFO Database Record (c) 2012 APA, all rights reserved)
  • Article
    The present paper extends the coverage of the "Psychological Record" (1977) devoted to the topic of tonic immobility (also known as "animal hypnosis") by examining the applicability of the designation tonic immobility to special states of behavioral inhibition in humans, particularly the occurrence of rape-induced paralysis commonly reported by rape victims. Since fear, overtones of predation, contact, and restraint are common denominators to rape and the induction of tonic immobility, and because the reactions by rape victims are often isomorphic with behaviors shown by immobilized animals, it is concluded that tonic immobility and rape-induced paralysis represent the same phenomenon. The adaptive value of this reaction to rape is briefly discussed. (24 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
  • Chapter
    review experimental [animal] models of anxiety, depression and post-traumatic stress and their relevance to human experience during and after torture / focused on the most commonly reported forms of torture by the survivors we have interviewed / [focus on] coping strategies under captivity and torture . . . which are illuminated by research on unpredictability and uncontrollability / divide discussion of torture experiences into these four phases / 1) pre-arrest/detention phase, 2) detention/torture, 3) trial/imprisonment, and 4) post-imprisonment phase / these four phases roughly parallel questions that have been addressed about pretreatment and acute, short-term and long-term effects of unpredictable and/or uncontrollable aversive events (PsycINFO Database Record (c) 2012 APA, all rights reserved)
  • Article
    Reviews data from a series of studies designed to test the hypothesis that tonic immobility (TI) represents an innate fear-potentiated response. In experiments using mostly 3–4 wk old Production Red chickens, fear was operationally defined by behavioral changes associated with long immobility reactions (i.e., defecation) and by certain manipulations, including (a) tranquilization, (b) intense auditory stimulation, (c) punishment, and (d) predatory confrontation with live and simulated stimuli, artificial eyes, and a visual cliff. Findings suggest that fear, while not the cause of TI, is an important antecedent condition for manipulating response duration and susceptibility. (61 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
  • The study of primate socio-ecology is in transition. The general hypothesis that ecology affects social behavior is still accepted, but there has been much recent debate over how it does so and the extent to which other factors, such as sexual conflict and phylogeny, are responsible for some patterns of primate sociality. The most important general finding in socio-ecology from the past three decades has been the recognition of distinct kinds of food competition and their effects on social relationships. Indirect or scramble competition limits group size but has relatively little affect on social relationships, whereas aggressive or contest competition between group members promotes kin-based alliances. The benefits of living in groups are being reevaluated - lowering of predation risk in larger groups is widely assumed, but supporting data are sometimes difficult to evaluate. Whatever the benefits of group living, they fail to explain a distinctive primate feature: prolonged social relationships between the sexes even outside of the breeding period. Recently, infanticide by males has been suggested as the main reason females may seek out or tolerate permanent association with males in most primate species. Evaluating the relative contributions of food competition, predation risk, and infanticide avoidance in structuring primate social relationships remains a challenge for the future. Meanwhile, it is important to recognize that species may not show adaptive behavior when their environment changes rapidly. This limitation may become an important aspect of future primate studies as tropical habitats the world over become increasingly influenced by human activity.
  • Article
    This article reviews research concerning the possible relationship between tonic immobility (TI) and human reactions to sexual assault. This review includes a description of the characteristic features of TI and a discussion of the most widely accepted theoretical explanation for TI. The possibility that humans may exhibit TI is explored and conditions that might elicit TI in humans are identified. In particular, we focus on TI in the context of sexual assault, because this form of trauma often involves elements that are necessary for the induction of TI in nonhuman animals, namely, fear and perceived physical restraint. The important similarities and differences in how TI manifests in humans and nonhuman animals are highlighted, future research directions are offered, and clinical implications are suggested.
  • Article
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    Many of the body's adaptive responses, such as pain, fever, and fear, are defenses that remain latent until they are aroused by cues that indicate the presence of a threat. Natural selection should shape regulation mechanisms that express defenses only in situations where their benefits exceed their costs, but defenses are often expressed in situations where they seem unnecessary, with much resulting useless suffering. An explanation emerges from a signal detection analysis of the costs and benefits that shaped defense regulation mechanisms. Quantitative modeling of optimal regulation for all-or-none defenses and for continuously variable defenses leads to several conclusions. First, an optimal system for regulating inexpensive all-or-none defenses against the uncertain presence of large threats will express many false alarms. Second, the optimum level of expression for graded defenses is not at the point where the costs of the defense and the danger are equal, but is instead where the marginal cost of additional defense exceeds the marginal benefit. Third, in the face of uncertainty and skewed payoff functions, the optimal response threshold may not be the point with the lowest cost. Finally, repeated exposures to certain kinds of danger may adaptively lower response thresholds, making systems vulnerable to runaway positive feedback. While we await quantitative data that can refine such models, a general theoretical perspective on the evolution of defense regulation can help to guide research and assist clinical decision making.
  • Article
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    The hypervigilance, escape, struggle, tonic immobility, evolutionarily hardwired acute peritraumatic response sequence is important for clinicians to understand. Our commentary supplements the useful article on human tonic immobility (TI) by Marx, Forsyth, Gallup, Fusé, and Lexington (2008). A hallmark sign of TI is peritraumatic tachycardia, which others have documented as a major risk factor for subsequent posttraumatic stress disorder (PTSD). TI is evolutionarily highly conserved (uniform across species) and underscores the need for DSM-V planners to consider the inclusion of evolution theory in the reconceptualization of anxiety and PTSD. We discuss the relevance of evolution theory to a reconceptualization of acute dissociative-conversion symptoms and of epidemic sociogenic disorder (epidemic “hysteria”). Both are especially in need of attention in light of the increasing threat of terrorism against civilians. We provide other pertinent examples. ...................... Finally, evolution theory is not ideology driven (and makes testable predictions regarding etiology in both directions). For instance, we predicted that the unexpected finding that some disorders conceptualized in as innate phobias are in fact conditioned responses and thus better conceptualized as mild forms of PTSD. ...................... ............................................ NOTE If you enjoyed reading this paper you should next read: BRACHA 2006 . Human brain evolution and the TIME-DEPTH PRINCIPLE. Implications for the reclassification of fear-circuitry traits and for resilience to warzone-related PTSD
  • Article
    Ethology's renewed interest in developmental context coincides with recent insights from neurobiology and psychology on early attachment. Attachment and social learning are understood as fundamental mechanisms in development that shape core processes responsible for informing behaviour throughout a lifetime. Each field uniquely contributes to the creation of an integrated model and encourages dialogue between Tinbergen's four analytical levels: ethology in its underscoring of social systems of behaviour and context, psychology in its emphasis on socio-affective attachment transactions, and neuroscience in its explication of the coupled development of brain and behaviour. We review the relationship between developmental context and behaviour outcome as a topic shared by the three disciplines, with a specific focus on underlying neuroethological mechanisms. This interdisciplinary convergence is illustrated through the example of abnormal behaviour in wild African elephants (Loxodonta africana) that has been systematically observed in human-caused altered social contexts. Such disruptions impair normative socially mediated neuroendocrinological development leading to psychobiological dysregulation that expresses as non-normative behaviour. Aberrant behaviour in wild elephants provides a critical field example of what has been established in ex situ and clinical studies but has been largely absent in wild populations: a concrete link between effects of human disturbance on social context, and short- and long-term neuroethology. By so doing, it brings attention to the significant change in theories of behaviour that has been occurring across disciplines – namely, the merging of psychobiological and ethological perspectives into common, cross-species, human inclusive models.
  • Article
    Some inadequacies of the classical conditioning analysis of phobias are discussed: phobias are highly resistant to extinction, whereas laboratory fear conditioning, unlike avoidance conditioning, extinguishes rapidly; phobias comprise a nonarbitrary and limited set of objects, whereas fear conditioning is thought to occur to an unlimited range of conditioned stimuli. Furthermore, phobias, unlike laboratory fear conditioning, are often acquired in one trial and seem quite resistant to change by “cognitive” means. An analysis of phobias using a more contemporary model of fear conditioning is proposed. In this view, phobias are seen as instances of highly “prepared” learning (Seligman, 1970). Such prepared learning is selective, highly resistant to extinction, probably noncognitive and can be acquired in one trial. A reconstruction of the notion of symbolism is suggested.
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    Defensive behaviors are evolved responses to threat, common to most mammalian species. Specific defenses may be differentiated anatomically at some brain sites and by responsivity to antianxiety drugs. Over-(or inappropriate) expression of specific defenses may contribute to the phenomenology of particular anxiety disorders.
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    Recent theories regarding the evolution of predator-prey interactions is reviewed. This includes theory about the dynamics and stability of both populations and traits, as well as theory predicting how predatory and anti-predator traits should respond to environmental change. Evolution can stabilise or destabilise interactions; stability is most likely when only the predator evolves, or when traits in one or both species are under strong stabilising selection. Stability seems least likely when there is coevolution and a bi-directional axis of prey vulnerability. When population cycles exist, adaptation may increase or decrease the amplitude of those cycles. An increase in the defensive ability of prey is less likely to produce evolutionary counter-measures in its partner than is a comparable increase in attack ability of the predator. Increased productivity may increase or decrease offensive and defensive adaptations. The apparent predominance of evolutionary responses of prey to predators over those of predators to prey is in general accord with equilibrium theory, but theory on stability may be difficult to confirm or refute. Recent work on geographically structured populations promises to advance our understanding of the evolution of predator-prey interactions.
  • Article
    Through the analysis of case studies of chimpanzees (Pan troglodytes troglodytes) in residence at a sanctuary, who previously sustained prolonged captivity and biomedical experimentation, we illustrate how human psychological models of diagnosis and treatment might be approached in great apes. This study reflects growing attention to ethical, scientific, and practical problems associated with psychological well-being of animals. The analysis concludes that a diagnosis of Complex PTSD in chimpanzees is consistent with descriptions of trauma-induced symptoms as described by the DSM-IV and human trauma research. We discuss how these findings relate to diagnosis and treatment of chimpanzees in captivity and the issue of their continued laboratory use. This clinical study contributes toward theory and therapeutic practices of an emergent trans-species psychology inclusive of both humans and other species. Such an ability to extend what we know about models of human trauma opens deeper understanding and insights into ourselves as well as individuals from other species.
  • Article
    This study evaluated whether tonic immobility mediates the relations between perceived inescapability, peritraumatic fear, and posttraumatic stress disorder (PTSD) symptom severity among sexual assault survivors. Female undergraduates (N = 176) completed questionnaires assessing assault history, perceived inescapability, peritraumatic fear, tonic immobility, and PTSD symptoms. Results indicated that tonic immobility fully mediated relations between perceived inescapability and overall PTSD symptom severity, as well as reexperiencing and avoidance/numbing symptom clusters. Tonic immobility also fully mediated the relation between fear and reexperiencing symptoms, and partially mediated relations between fear and overall PTSD symptom severity, and avoidance/numbing symptoms. Results suggest that tonic immobility could be one path through which trauma survivors develop PTSD symptoms. Further study of tonic immobility may inform our ability to treat trauma victims.
  • Article
    The coping behavior of rape victims can be analyzed in three distinct phases--the threat of attack, the attack itself, and the period immediately thereafter. The authors analyzed the reported coping behavior of 92 women diagnosed as having rape trauma. Most of the women used verbal, physical, or cognitive strategies when threatened, although 34 were physically or psychologically paralyzed. The actual rape prompted coping behaviors in all but 1 victim. Escaping the situation or the assailant is the primary task immediately after the attack. In counseling the rape victim, it is important to understand her individual style of coping, to be supportive of it, and to suggest alternatives for future stressful situations.
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    The disturbances observed in animals subjected to unpredictable and uncontrollable aversive events resemble post-traumatic stress disorder (PTSD) symptoms and thus may constitute an animal model of this disorder. It is argued that the similarity between animals' symptoms and those of trauma victims may reflect common etiological factors. Relevant experiments in which animals exhibit generalized fear and arousal, discrete fear of a conditioned stimulus (CS), analgesia, and avoidance are reviewed with the view that these manifestations may be analogous to the PTSD symptom clusters of persistent arousal, reexperiencing, numbing, and avoidance, respectively. Finally, animal paradigms are suggested to test the validity of the model and specific hypotheses are derived from the animal literature regarding trauma variables that are predictive of particular PTSD symptom clusters.
  • Article
    Two experiments examined whether superior observational conditioning of fear occurs in observer rhesus monkeys that watch model monkeys exhibit an intense fear of fear-relevant, as compared with fear-irrelevant, stimuli. In both experiments, videotapes of model monkeys behaving fearfully were spliced so that it appeared that the models were reacting fearfully either to fear-relevant stimuli (toy snakes or a toy crocodile), or to fear-irrelevant stimuli (flowers or a toy rabbit). Observer groups watched one of four kinds of videotapes for 12 sessions. Results indicated that observers acquired a fear of fear-relevant stimuli (toy snakes and toy crocodile), but not of fear-irrelevant stimuli (flowers and toy rabbit). Implications of the present results for the preparedness theory of phobias are discussed.
  • Article
    Notes that animal hypnosis, or tonic immobility, is an easily induced and readily quantifiable phenomenon found in many different species. Recent findings on the behavioral, ecological, chemical, neurological, genetic, and ontogenetic aspects of animal hypnosis are reviewd in light of current and historical interpretations. The response seems to be quite sensitive to manipulations designed to affect fear. In terms of adaptive significance, the reaction can be modified through selective breeding, and both naturalistic as well as laboratory investigations bolster the thesis that tonic immobility may participate in the ecology of predator-prey relationships. (93 ref)
  • Article
    Defensive behaviors comprise a set of flexible and adaptive responses to threatening situations and stimuli. In semi-natural situations affording a wide variety of responses, defensive behaviors change over time in response to information about the presence of danger, acquired through risk assessment activities. Two test batteries, a Fear/Defense Test Battery (F/DTB) measuring defensive behaviors to present, approaching predators, and an Anxiety/Defense Test Battery (A/DTB) measuring reactions to potential threat, have been used in conjunction with administration of potentially anxiolytic drugs. Results suggest that the F/DTB behaviors are not systematically responsive to anxiolytics. However, on the A/DTB, anxiolytic benzodiazepines produce a profile of effects primarily involving risk assessment activities. Very similar profiles of effect are seen also with some 5-HT1A compounds, alcohol, imipramine and MK-801, but not for a variety of additional compounds. A consistent pattern of gender differences are obtained with the A/DTB, with females more defensive than males. These results indicate that particular patterns of defensive behaviors may provide a very appropriate animal model for the analysis of pharmacological effects on anxiety.
  • Article
    How close should an animal allow a potential predator to approach before fleeing to a refuge? Fleeing too soon wastes time and energy that could be spent on other important activities, but fleeing too late is potentially lethal. A model to predict flight initiation distance was developed, based on the assumption that animals would flee at a distance that allows them to reach the refuge ahead of the predator by some margin of safety. This model predicts that (1) flight initiation distance should increase with distance from the refuge (which has been supported by studies on several species) and (2) the rate of increase of flight initiation distance with distance from a refuge should be higher when the refuge is between the predator and prey (prey runs towards the predator) than when the prey is between the predator and the refuge (prey runs away from the predator). Prediction 2 was tested by approaching juvenile woodchucks, Marmota monaxalong an imaginary line between the animal and its burrow entrance and measuring the distance between the observer and the animal at the moment it started its flight. As predicted, the rate of increase in flight initiation distance was higher when the burrow was between the observer and the woodchuck than when the woodchuck was between the observer and the burrow. The slopes were appropriate for predators with pursuit speeds about twice the escape speed of the woodchucks. The difference between the slopes was 1.78 m flight distance/m distance to refuge, close to the value of 2 m flight distance/m distance to refuge predicted by the model. The intercept indicated that woodchucks allowed a margin of safety of about 7.6 m. The model permits quantitative evaluation of the principal elements of flexible escape decisions of animals and provides a measure of how predation risk increases the cost of space use in relation to distance from a refuge.
  • Article
    Patients with complex dissociative disorders remain in alternating psychophysiological states which are discrete, discontinuous, and resistant against integrative tendencies. In this contribution, a parallel is drawn between animal defensive and recuperative states that are evoked in the face of severe threat and the characteristic responses of dissociative disorder patients as displayed in major dissociative states. Empirical data and clinical observations seem to be supportive of the idea that there are similarities between freezing, concomitant development of analgesia and anesthesia, and acute pain in threatened animals and severely traumatized human beings.
  • Article
    Contemporary learning theories of posttraumatic stress disorder (PTSD) provide an explanation for the phobic avoidant features but do not account fully for the intrusive phenomena that are so characteristic of the disorder. This article hypothesizes that a primitive learning center in the limbic system rehearses traumatic memories immediately following exposure to trauma, thus inducing durable memories of the sources of novel threat. It is postulated that the mechanism developed during early evolution when, in the absence of cognitive mechanisms, automatic learning following single exposure to novel threat would have conferred survival value on the species. With evolution of the brain, a second cortical pathway developed for the cognitive processing of trauma memories. It is possible that synchrony between the two phylogentically distinct pathways may be lost in vulnerable individuals under conditions of extreme stress resulting in failure of cortical inhibition of limbic trauma rehearsal mechanisms. A mismatch between archaic biological mechanisms and novel cues in the modern environment also may play a role in triggering traumatic memories and associated fight and flight reactions. The intrusive phenomena of PTSD thus may reflect an "overlearned survival response" in those in whom the putative limbic rehearsal mechanism evades cortical control. The heuristic value and limitations of such an evolutionary-learning theory are discussed.
  • Article
    Tonic immobility (TI) is thought to represent the terminal reaction in the chain of antipredatory responses involved in maintaining survival. TI is an inhibitory behavioral response in which the animal presents a significant decrease in body activity and responsiveness to the environment induced by some form of physical restraint. This response is induced in the laboratory by inversion of the animal and brief postural contention of its movements. In nature, the TI response may be triggered by some threatening or predatory stimulus, indicating the physical contact between response occurs when there is physical contact between prey and predator. In this case, the physical inactivity of the prey may prevent the continuation of the attack. The neural substrate of this response is not well known, and the objective of the present study was to investigate the effect of cholinergic stimulation of amygdala regions on TI modulation in guinea pigs. Microinjection of carbachol (0.5 microg/0.2 microL) into the central (CEA), basolateral (BLA), and lateral posterior (LPA) nuclei of the amygdala promoted a reduction in the duration of TI episodes. Pretreatment with atropine (0.5 microg/0.2 microL) showed that the action of carbachol is mediated by muscarinic receptors.
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    Full-text available
    An interview study of 81 former political prisoners investigated whether posttraumatic stress disorder (PTSD) is related to the way individuals process the prison experience. In contrast to participants without PTSD, those with chronic or remitted PTSD were more likely to perceive mental defeat and an overall feeling of alienation from other people. Chronic PTSD was also related to perceived negative and permanent change in their personalities or life aspirations. The groups did not differ in their attempts to gain control during imprisonment. Evidence for a relationship between political commitment and PTSD was mixed. The results suggest that mental defeat, alienation, and permanent change are related to PTSD after interpersonal trauma and may need to be addressed in treatment.
  • Article
    The aim of this paper is to explicate what is special about emotional information processing, emphasizing the neural foundations that underlie the experience and expression of fear. A functional, anatomical model of defense behavior in animals is presented and applications are described in cognitive and physiological studies of human affect. It is proposed that unpleasant emotions depend on the activation of an evolutionarily primitive subcortical circuit, including the amygdala and the neural structures to which it projects. This motivational system mediates specific autonomic (e.g., heart rate change) and somatic reflexes (e.g., startle change) that originally promoted survival in dangerous conditions. These same response patterns are illustrated in humans, as they process objective, memorial, and media stimuli. Furthermore, it is shown how variations in the neural circuit and its outputs may separately characterize cue-specific fear (as in specific phobia) and more generalized anxiety. Finally, again emphasizing links between the animal and human data, we focus on special, attentional features of emotional processing: The automaticity of fear reactions, hyper-reactivity to minimal threat-cues, and evidence that the physiological responses in fear may be independent of slower, language-based appraisal processes.
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    Here we provide a review of the animal and human literature concerning the role of the amygdala in fear conditioning, considering its potential influence over autonomic and hormonal changes, motor behavior and attentional processes. A stimulus that predicts an aversive outcome will change neural transmission in the amygdala to produce the somatic, autonomic and endocrine signs of fear, as well as increased attention to that stimulus. It is now clear that the amygdala is also involved in learning about positively valenced stimuli as well as spatial and motor learning and this review strives to integrate this additional information. A review of available studies examining the human amygdala covers both lesion and electrical stimulation studies as well as the most recent functional neuroimaging studies. Where appropriate, we attempt to integrate basic information on normal amygdala function with our current understanding of psychiatric disorders, including pathological anxiety.
  • Article
    The collection of articles in this issue constitutes the most thorough review of posttraumatic stress disorder (PTSD) yet. At this point, the accumulated phenomenological, epidemiological, biological, and treatment evidence make it crystal clear that PTSD stands alone as a unique psychiatric disorder. It is not the same as depression, although many PTSD patients are also depressed, and it is not the same as the other anxiety disorders, although PTSD patients frequently also suffer with panic attacks, social avoidance, and obsessive ruminations.
  • Article
    The experience of a single threatening situation may alter the behavior of an animal in a long-lasting way. Long-lasting changes in behavior have been induced in laboratory animals to model and investigate the development and neural substrate of human psychopathologies. Under natural conditions, however, changes in behavior after an aversive experience may be adaptive because behavioral modifications allow animals to adjust to a threat for extended periods of time. In the laboratory setting, properties of the aversive situation and the potential of the animal to respond to the threat may be altered and lead to extensive, prolonged changes, indicating a failure in behavioral regulation. Such long-term changes seem to be mediated by neuronal alterations in components of the fear pathway. To understand psychopathologies, determinants of exaggerated responsivity and the underlying molecular and neural processes have to be analyzed in a comparative way under conditions that produce normal and abnormal fear and anxiety.
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    Catatonia, long viewed as a motor disorder, may be better understood as a fear response, akin to the animal defense strategy tonic immobility (after G. G. Gallup & J. D. Maser, 1977). This proposal, consistent with K. L. Kahlbaum's (1874/1973) original conception, is based on similarities between catatonia and tonic immobility ("death feint") as well as evidence that catatonia is associated with anxiety and agitated depression and responds dramatically to benzodiazepines. It is argued that catatonia originally derived from ancestral encounters with carnivores whose predatory instincts were triggered by movement but is now inappropriately expressed in very different modern threat situations. Found in a wide range of psychiatric and serious medical conditions, catatonia may represent a common "end state" response to feelings of imminent doom and can serve as a template to understand other psychiatric disorders.
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    Full-text available
    Directional inference: scientific convention applies conclusions from animal studies to humans but not the reverse, contradicting current evidence.
  • Article
    Postural sway and heart rate were recorded in young men viewing emotionally engaging pictures. It was hypothesized that they would show a human analog of "freezing" behavior (i.e., immobility and heart rate deceleration) when confronted with a sustained block of unpleasant (mutilation) images, relative to their response to pleasant/arousing (sport action) or neutral (objects) pictures. Volunteers stood on a stabilometric platform during picture viewing. Significantly reduced body sway was recorded during the unpleasant pictures, along with increased mean power frequency (indexing muscle stiffness). Heart rate during unpleasant pictures also showed the expected greater deceleration. This pattern resembles the "freezing" and "fear bradycardia" seen in many species when confronted with threatening stimuli, mediated by neural circuits that promote defensive survival.
  • Article
    The present study examined tonic immobility (TI) in victims of childhood sexual abuse (CSA). Female undergraduates (n=39) and female psychiatric inpatients (n=41) who experienced CSA completed a series of questionnaires assessing aspects of their victimization history, psychological functioning, and TI symptoms. Over fifty-two percent of all participants reported TI in response to CSA. Episodes of CSA involving attempted or completed penile/vaginal penetration were more likely to be associated with an increased likelihood of experiencing TI, and report of TI was associated with greater current psychological impairment. The implications of these findings are discussed, and suggestions for future research are offered.
  • Article
    Freezing, fleeing or fighting back are general defensive responses in many taxa. These defenses are mutually exclusive, since a prey cannot simultaneously flee and fight, or freeze and flee. Each of these defenses by itself is rudimentary and probably cannot provide a completely effective means to elude predation. Freezing is efficient only if employed before the prey is spotted by the predator, otherwise the prey becomes a stationary, easy to catch target. In fleeing, the prey can move directly away and maximize its distance from the predator, move toward the predator to confine it to a single clashing point, or dodge sideways to evade the attack. Prey can also run in a straight path that is efficient against slow or distant predators, or in a zigzag path that is efficient when a raptor is close or fast. In all, freezing and fleeing constitute together a complex and flexible defensive response, and are probably controlled by different motor systems that are inter-connected to allow fast switching between these behaviors, as required for an effective and versatile response.
  • Article
    This paper reviews recent work which points to critical neural circuitry involved in lasting changes in anxiety like behavior following unprotected exposure of rats to cats (predator stress). Predator stress may increase anxiety like behavior in a variety of behavioral tests including: elevated plus maze, light dark box, acoustic startle, and social interaction. Studies of neural transmission in two limbic pathways, combined with path and covariance analysis relating physiology to behavior, suggest long term potentiation like changes in one or both of these pathways in the right hemisphere accounts for stress induced changes in all behaviors changed by predator stress except light dark box and social interaction. Findings will be discussed within the context of what is known about neural substrates activated by predator odor.