Muriel A. Hagenaars

Facing Freeze Social Threat Induces Bodily Freeze in Humans

Freezing is a common defensive response in animals threatened by predators. It is characterized by reduced body motion and decreased heart rate (bradycardia). However, despite the relevance of animal defense models in human stress research, studies have not shown whether social threat cues elicit similar freeze-like responses in humans. We investigated body sway and heart rate in 50 female participants while they were standing on a stabilometric force platform and viewing cues that were socially threatening, socially neutral, and socially affiliative (angry, neutral, and happy faces, respectively). Posturographic analyses showed that angry faces (compared with neutral faces and happy faces) induced significant reductions in body sway. In addition, the reduced body sway for angry faces was accompanied by bradycardia and correlated significantly with subjective anxiety. Together, these findings indicate that spontaneous body responses to social threat cues involve freeze-like behavior in humans that mimics animal freeze responses. These findings open avenues for studying human freeze responses in relation to various sociobiological markers and social-affective disorders.

The impact of dissociation and depression on the efficacy of prolonged exposure treatment for PTSD

This study investigates the impact of dissociative phenomena and depression on the efficacy of prolonged exposure treatment in 71 patients with posttraumatic stress disorder (PTSD). Diagnoses, comorbidity, pretreatment depressive symptoms, PTSD symptom severity, and dissociative phenomena (trait dissociation, numbing, and depersonalization) were assessed at pretreatment using semi-structured interviews and questionnaires. In a pretreatment behavioral exposure test, patients were imaginally exposed to (part of) their trauma memory for 9 min, during which subjective fear was assessed. At posttreatment and 6 months follow-up PTSD, depressive and dissociative symptoms were again assessed in the completers (n = 60). Pretreatment levels of dissociative and depressive symptoms were similar in dropouts and completers and none of the dissociative phenomena nor depression predicted improvement. Against expectations, dissociative phenomena and depression were associated with enhanced rather than impeded fear activation during the behavioral exposure test. However, these effects disappeared after controlling for initial PTSD severity. Hence, rather than supporting contraindication, the current results imply that patients presenting with even severe dissociative or depressive symptoms may profit similarly from exposure treatment as do patients with minimal dissociative or depressive symptoms.

Fear activation and habituation patterns as early process predictors of response to prolonged exposure treatment in PTSD

Improved (n = 21) and nonimproved (n = 13) PTSD patients (a mixed trauma population) were compared for fear activation and habituation patterns during and between the 1st and 2nd prolonged exposure sessions. Drop-outs (n = 11) were also evaluated. Nonimproved patients had significantly higher ratings of anxiety at the start of the first exposure session. Improved patients showed more within-session habituation during the self-exposures at home and more between-session habituation. Even after controlling for initial PTSD and depression symptom severity, habituation between the first and second exposure sessions was significantly related to treatment outcome. Patients who dropped out of the treatment were found not to differ from completers on fear activation and within-session habituation during the first exposure session.

Updating freeze: aligning animal and human research.

Freezing is widely used as the main outcome measure for fear in animal studies. Freezing is also getting attention more frequently in human stress research, as it is considered to play an important role in the development of psychopathology. Human models on defense behavior are largely based on animal models. Unfortunately, direct translations between animal and human studies are hampered by differences in definitions and methods. The present review therefore aims to clarify the conceptualization of freezing. Neurophysiological and neuroanatomical correlates are discussed and a translational model is proposed. We review the upcoming research on freezing in humans that aims to match animal studies by using physiological indicators of freezing (bradycardia and objective reduction in movement). Finally, we set the agenda for future research in order to optimize mutual animal-human translations and stimulate consistency and systematization in future empirical research on the freezing phenomenon.

Aversive life events enhance human freezing responses

In the present study, we investigated the effect of prior aversive life events on freezing-like responses. Fifty healthy females were presented neutral, pleasant, and unpleasant images from the International Affective Picture System while standing on a stabilometric platform and wearing a polar band to assess body sway and heart rate. In the total sample, only unpleasant pictures elicited reduced body sway and reduced heart rate (freezing). Moreover, participants who had experienced 1 or more aversive life events showed greater reductions in heart rate for unpleasant versus pleasant pictures than those who had experienced no such event. In addition, relative to no-event participants, single-event participants showed reduced body sway to unpleasant pictures, while multiple-event participants showed reduced body sway in response to all picture categories. These results indicate that aversive life events affect automatic freezing responses and may indicate the cumulative effect of multiple trauma. The experimental paradigm presented is a promising method to study freezing as a primary defense response in trauma-related disorders.

Walk to me when I smile, step back when I'm angry: emotional faces modulate whole-body approach-avoidance behaviors.

Facial expressions are potent social cues that can induce behavioral dispositions, such as approach–avoidance tendencies. We studied these tendencies by asking participants to make whole-body forward (approach) or backward (avoidance) steps on a force plate in response to the valence of social cues (happy or angry faces) under affect-congruent and incongruent mappings. Posturographic parameters of the steps related to automatic stimulus evaluation, step initiation (reaction time), and step execution were determined and analyzed as a function of stimulus valence and stimulus–response mapping. The main result was that participants needed more time to initiate a forward step towards an angry face than towards a smiling face (which is evidence of a congruency effect), but with backward steps, this difference failed to reach significance. We also found a reduction in spontaneous body sway prior to the step with the incongruent mapping. The results provide a crucial empirical link between theories of socially induced action tendencies and theories of postural control and suggest a motoric basis for socially guided motivated behavior.

The effect of trauma onset and frequency on PTSD-associated symptoms

BACKGROUND Different trauma characteristics have been suggested to lead to distinct symptom profiles. This study investigates the effect of two trauma characteristics, age of onset and frequency, on PTSD symptom profiles. METHODS Trauma characteristics (childhood versus adulthood trauma and single versus multiple trauma), psychiatric diagnosis, PTSD severity, depressive symptoms, dissociation, guilt, shame, anger, and interpersonal sensitivity were assessed in 110 PTSD outpatients. RESULTS Single versus multiple trauma and childhood versus adulthood trauma groups did not differ in depressive symptom and co-morbidity. Multiple trauma patients reported more dissociation, guilt, shame, and interpersonal sensitivity than those that experienced single trauma. Anger of multiple trauma patients was more often directed towards themselves, whereas anger in single trauma patients was more often directed towards others. Childhood trauma patients reported more dissociation and state anger than adulthood trauma patients. However, with the exception of multiple trauma patients having more dissociation and shame than those with single trauma, all differences disappeared after controlling for PTSD severity. LIMITATIONS This study is a first step in unraveling the impact of different trauma characteristics. Causal inferences are limited, though, because of the cross-sectional design. CONCLUSIONS The results suggest that experiencing trauma at young age or multiple times may lead to different symptom profiles but these are, with the exception of dissociation and shame, dependent on PTSD severity. These results support the proposed DSM-V criteria in which these symptoms appear as part of the disorder, and stress the importance of early treatment.

Intrusive images and intrusive thoughts as different phenomena: Two experimental studies

According to the dual representation theory of PTSD, intrusive trauma images and intrusive verbal thoughts are produced by separate memory systems. In a previous article it was shown that after watching an aversive film, participants in non-movement conditions reported more intrusive images than participants in a free-to-move control condition (Hagenaars, Van Minnen, Holmes, Brewin, & Hoogduin, 2008). The present study investigates whether the experimental conditions of the Hagenaars et al. study had a different effect on intrusive thoughts than on intrusive images. Experiment 2 further investigated the image–thoughts distinction by manipulating stimulus valence (trauma film versus neutral film) and assessing the subsequent development of intrusive images and thoughts. In addition, both experiments studied the impact of peri-traumatic emotions on subsequent intrusive images and thoughts frequency across conditions. Results showed that experimental manipulations (non-movement and trauma film) caused higher levels of intrusive images relative to control conditions (free movement and neutral film) but they did not affect intrusive thoughts. Peri-traumatic anxiety and horror were associated with subsequent higher levels of intrusive images, but not intrusive thoughts. Correlations were inconclusive for anger and sadness. The results suggest intrusive images and thoughts can be manipulated independently and as such can be considered different phenomena.

The effect of hypnotically induced somatoform dissociation on the development of intrusions after an aversive film

Peritraumatic dissociation is thought to effect trauma information encoding, leading to PTSD symptoms like intrusive memories. Most studies have focused on peritraumatic psychological dissociation. The present experiment studied the impact of hypnotically induced somatoform dissociation (dissociative non-movement) versus deliberate non-movement during an aversive film on intrusion development. Seventy-nine participants were randomised into three conditions: dissociative non-movement (catalepsy), deliberate non-movement, and non-restricted control. Participants recorded their intrusions of the film in a diary for one week. In the dissociative non-movement condition, catalepsy effectively provoked somatoform dissociation. Spontaneous somatoform dissociation across conditions was positively related to implicit bias to film-related words and negatively related to explicit recall, but was not related to intrusion frequency. Dissociative non-movement and deliberate non-movement conditions combined had more intrusions than controls. However, the dissociative non-movement group did not have more intrusions than deliberate non-movement and control groups combined. The implications of these findings are discussed.

The trauma film paradigm as an experimental psychopathology model of psychological trauma: intrusive memories and beyond.

A better understanding of psychological trauma is fundamental to clinical psychology. Following traumatic event(s), a clinically significant number of people develop symptoms, including those of Acute Stress Disorder and/or Post Traumatic Stress Disorder. The trauma film paradigm offers an experimental psychopathology model to study both exposure and reactions to psychological trauma, including the hallmark symptom of intrusive memories. We reviewed 74 articles that have used this paradigm since the earliest review (Holmes & Bourne, 2008) until July 2014. Highlighting the different stages of trauma processing, i.e. pre-, peri- and post-trauma, the studies are divided according to manipulations before, during and after film viewing, for experimental as well as correlational designs. While the majority of studies focussed on the frequency of intrusive memories, other reactions to trauma were also modelled. We discuss the strengths and weaknesses of the trauma film paradigm as an experimental psychopathology model of trauma, consider ethical issues, and suggest future directions. By understanding the basic mechanisms underlying trauma symptom development, we can begin to translate findings from the laboratory to the clinic, test innovative science-driven interventions, and in the future reduce the debilitating effects of psychopathology following stressful and/or traumatic events.