Michael C. Anderson, Adam Aron, David Badre, Bernard W. T.Balleine, Marie Banich, Anya K. Bershad, Antonello Bonci, Michael B. Bonsall,Katheen T. Brady, Judson Brewer, Michael R. Bruchas, David M. Buss, Aurelio Cortese, Hugo D. Critchley, Damiaan Denys, Harriet de Wit, Lisa Espinosa, John R. Fedota, Shelly B. Flagel, Aikaterina Fotopoulou, Sophia Frangou, Karl Friston, Rita Z. Goldstein, Shannon L. Gourley, Suzanne N. Haber, Colleen A. Hanlon, Andreas Heinz, Emily A. Holmes, Quentin J. M, Huys, Peter W. Kalivas, Laura Kress, Hakwan Lau, Kayuet Liu, Tiago V. Maia, Lisa M. McTeague, Amy L. Milton, Marie Hélène Monfils, Martin P. Paulus, Paul E. M. Phillips, Marina R. Picciotto, Trevor W. Robbins, Angels C. Roberts, Daniela Schiller, Florian Schlagenhauf, Jonathan W. Schooler, Jens V. Schwarzbach, Jeremy K. Seamans, Laura Singh, Eliot A. Stein, Peter Tse, Renée M. Visser, Martin Voss
This volume reports on the 30th Ernst Strüngmann Forum. It presents a synthesis of the ideas and perspectives that evolved over a two-year period and highlights questions that remain to be addressed through future work. For those seeking insight into the process, this brief overview is offered.
In 2017, Peter Kalivas and Martin Paulus approached me to discuss the possibility of proposing a theme on intrusive thinking. Having recently experienced another Ernst Strüngmann Forum on computational psychiatry (Redish and Gordon 2016), they were eager to subject the phenomenon of intrusive thinking to intense examination and sought our help to create the requisite dialogue. Their proposal provided the impetus, but as anyone who has been involved with our approach will tell you, one never knows where the discourse will ultimately lead as perspectives from other experts become available.
After the proposal was accepted, Katerina Fotopoulou, Rita Goldstein, Trevor Robbins, and Peter Tse joined us on the Program Advisory Committee to construct a framework that would support a dynamic, multidisciplinary discussion. The committee delineated discussion topics, identified potential participants, and formulated overarching goals:
In addition, four primary themes were established around which the discussion would unfold and key questions were proposed for each working group to consider. In advance, invited papers transmitted information on specific topics to a diverse group of experts (from behavioral neuroscience, cognitive neuroscience, neuroimaging, theoretical neurobiology, psychiatry, computational neuroscience/psychiatry, philosophy, and neuropsychopharmacology), who gathered in Frankfurt am Main, Germany, from June 14–19, 2019, for a most lively discussion.
A summary of this exchange is captured here in this volume. Organized around the primary themes, it contains the background papers in their finalized form (i.e., after peer review and revision) as well as the summary reports from each working group (Chapters 5, 9, 13, and 17).
As you approach this book, it is important to realize that a Forum is not a linear process. The framework put into place was designed to guide, not constrain, the discussion. Indeed, alternative perspectives were cultivated at each stage. Within this dynamic setting, replete with multiple and often divergent viewpoints, topics emerged that could not be resolved. These issues, highlighted in the individual chapters, are evidence of a fruitful exchange, and it is our hope that they will be used to stimulate future enquiry and action.
An endeavor of this kind creates unique group dynamics and puts demands on everyone who participates. Throughout, each contributor played an active role, and for their efforts and time, I express my gratitude. A special word of thanks goes to the Program Advisory Committee, to the authors and reviewers of the background papers, as well as to the moderators of the individual working groups (Antonello Bonci, Peter Tse, Trevor Robbins, and Rita Goldstein). Further, Shannon Gourley, Renée Visser, Angela Roberts, and Judson Brewer deserve special recognition: as rapporteurs for the working groups, they skillfully guided the preparation and finalization of their group’s report. Importantly, I wish to extend my sincere appreciation to Peter Kalivas and Martin Paulus, whose vision and commitment were essential to the successful realization of this Forum.
The Ernst Strüngmann Forum is able to conduct its work due to the institutional stability provided by the Ernst Strüngmann Foundation, established by Dr. Andreas and Dr. Thomas Strüngmann in honor of their father, Dr. Ernst Strüngmann. As a tribute to his life’s work, the Ernst Strüngmann Forum promotes scientific collaboration among international researchers, with the aim of expanding knowledge in basic science and identifying future research directions. Valuable partnerships accompany our work: The Scientific Advisory Board of the Ernst Strüngmann Forum ensures the scientific independence of the Forum. The Deutsche Forschungsgemeinschaft provided supplemental financial support for this Forum, and the Frankfurt Institute for Advanced Studies shares its vibrant intellectual setting with us.
Expanding the boundaries to knowledge is not an easy enterprise. Yet as limitations in current understanding start to come into focus, the act of formulating strategies to move forward becomes a most invigorating experience. Results from the brain-storming at this Forum have already started to influence ongoing research. It is our hope that this volume will spur further opportunities and lead ultimately to the creation of novel interventions that are capable of easing the suffering brought about by the phenomenon of intrusive thinking.
Have you ever wondered why thoughts appear and can motivate you to do things you wouldn’t otherwise do? One afternoon, Sue (my wife) called me at work to tell me she was going out with friends after work, and it was up to me to get dinner and do homework with the kids. Sue and her messages were (and remain to this day) very motivating for me, so I packed up and went down to my car. On the way to the car and during the drive home, I randomly thought about what I would cook for dinner, which kid was having a test and would need help, and various other plans for the evening. About halfway home, Kyle from the pub called. He was energized because a buddy from southern California had just flown in and thus Kyle was rounding people up for what sounded like a really fun night. I was going to tell him, “Sorry, I can’t make it,” but then the 20 beers on tap suddenly popped into my mind, as did the hilarious time we had the last time we all got together. Pretty soon I wasn’t thinking about dinner plans or school tests any more. I was making plans to be with my friends and thinking about the latest release IPA from the local microbrewery. When we ended our call, I had told him that I wasn’t sure what I would do. At this point, we might ask ourselves what is more motivating: going home to cooking and homework, or going to the pub for beer and friends. Each one of us faces these types of decisions, big and small, all the time, and what we do depends largely on how we organize our thoughts about each possible scenario and which ultimately seems most important to us. In this story, if you know Sue, you pretty much know already that I went home and had to hear about all of the pub hilarity the next morning. But, if I suffered from alcohol use disorder, thoughts about what would happen at the pub, the taste of the beer, and past really fun pub experiences would have inevitably intruded until they all but squeezed out thoughts of dinner and homework with my kids. My plans to go home would begin to fade until they were all but forgotten, or perhaps I would rationalize that stopping by for one of the special IPAs before going home would somehow work out.
The story above illustrates how thoughts of pub friends and beer can intrude in substance use disorder. However, the intrusion of traumatic events in posttraumatic stress disorder, rumination on negative outcomes in depression, or hearing voices in schizophrenia are all examples of thoughts generated by your brain that can contribute to debilitating psychiatric disorders. Of course, it is a natural and healthy adaptive process to produce thoughts either randomly or in association with the world we are experiencing, and then to use these thoughts to navigate successfully toward desired outcomes.
This volume explores and provides the best possible explanations for what this process is, how it gets usurped in psychiatric disorders, and what this knowledge of how the brain handles thoughts means for concepts of free will and one’s responsibility for poor decisions, especially when a thought disorder exists. It addresses how the brain is organized to create thoughts that can be ignored or can build in motivational content, and how we then weigh thoughts to decide on behavior that best adapts us to the world. It also poses and attempts to answer a number of questions that are commonly asked: How do the mechanisms of thought intrusion and decision making get corrupted in psychiatric disorders to create intrusions that cannot be controlled? How are thought intrusions usurped by motivation to produce behavior that may be maladaptive, at least according to social norms? What is free will and what responsibility does free will (or lack of it) create for how we behave?
Intrusive thinking has been defined as “any distinct, identifiable cognitive event that is unwanted, unintended, and recurrent. It interrupts the flow of thought, interferes in task performance, is associated with negative affect, and is difficult to control” (Clark 2005:4). Intrusive thinking is ubiquitous: it occurs as random, sometimes annoying daily interruptions but can also be a profoundly disabling symptom in almost all psychiatric disorders. Clinical examples include, but are not limited to, craving in drug addiction, recall of life-threatening events in posttraumatic stress disorder (PTSD), rumination in depression, and hallucinations in schizophrenia. The transdiagnostic nature of intrusive thought in neuropsychiatry points to the importance of understanding the genesis of the intrusions and how they can be therapeutically monitored and regulated. The neuroplasticity and circuitry that underpin intrusive thinking need to be clearly characterized in order to identify sensitive biomarkers and targets useful for translation into novel pharmacological and psychosocial treatments.
This 30th Ernst Strüngmann Forum brought together experts from a wide range of scientific disciplines to evaluate the current state of research into intrusive thinking and to define the boundaries of what is known and unknown about this perplexing and ubiquitous phenomenon. Using a dynamic cross-fertilization strategy of discovery (for more information, see the Preface), teams of experts from neurobiology, neuropsychiatry, and cognitive neuroscience explored four thematic areas: (a) molecular and circuits, (b) psychological cognitive processes, (c) system approaches and models, and (d) interventions and treatments. Within each working group, discussion centered on advancing research and treatment strategies, on identifying challenges to be addressed by future research, on developing models of intrusive thinking, and on the social and philosophical implications beyond its relevance for mental health. This volume, organized around the thematic areas of the working groups, synthesizes the multifaceted deliberations that took place in Frankfurt, Germany, from June 14–19, 2019.
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This chapter discusses psychological constructs considered to be central to the mediation of intrusive thinking and the neural circuits that underlie these processes. It assimilates intrusive thoughts with conditioned responses, discerns associate structures that can support these responses, and suggests how episodic information may be integrated with these associations. Mechanisms by which intrusive thoughts can be updated are explored, with a focus on extinction and memory reconsolidation. Intrusive thoughts ultimately engage many areas of the brain as they encompass sensory, cognitive, motor, and somatic processes. In this chapter, the focus is on specific circuits within the prefrontal-limbic network that are proposed to encode, update, and maintain the content of intrusions. These circuits include interconnecting pathways between the ventral tegmental area, nucleus accumbens, medial prefrontal and orbitofrontal cortices, hippocampus, and the amygdaloid complex.
The loop-like circuits which link the cortex and basal ganglia have been implicated in a range of functions; most recently in the precursors to movement, including planning and decision making. Damage to these circuits induced by various disease states have, therefore, been heavily implicated in a range of symptoms, including intrusive involuntary thoughts and actions associated with, for example, neurodegenerative and psychiatric conditions as well as addictions of various kinds. This chapter focuses on recent evidence of parallel circuits that mediate the distinct forms of control associated with reflexive and volitional actions, and the interactions between these circuits in determining adaptive behavior. It discusses two kinds of interaction important for understanding intrusive actions and thoughts: competitive interactions, whereby circuits controlling volitional actions regulate reflexive or habitual responses, and cooperative processes that allow the simulation of specific actions to become manifest in performance. It then explores the role of information derived from predictive learning in action selection and choice. The influence of such information is conveyed through a specific corticobasal ganglia circuit, damage to which has been implicated in compulsive action. The evidence considered generally suggests that intrusive thoughts and actions are the product of an imbalance between corticobasal ganglia circuits rather than dysfunction in any one circuit or its related control process.
A critical challenge in the field of neuroscience as well as research into the neurobiological basis of behavior has been to establish links between the cellular and biochemical processes within the brain and nervous system that occur during the mediation of behavioral events. Developments over the last 10–15 years have provided several new means to accelerate, advance, and dissect the specific mechanisms for brain function. Developments across two realms of neuroscience and engineering have afforded researchers, clinicians, and biologists advanced abilities to facilitate the dissection, observation, control, and perturbation of neural systems within intact, behaving animals. These advances include electrical, optical, pharmacological, and specialized hardware which allow for closed-loop interfaces to monitor and manipulate neural function. This chapter explores how these recent developments have become integrated into our neurobiological tool chest. It describes current advanced approaches, and the limitations of each, and explores future pathways toward even better technologies needed to dissect the molecular, cellular, and circuit basis of behavior.
Nonhuman experimental systems (also known as model organisms) are critical for understanding the neurobiology of intrusive thought. These model systems allow for the ability to manipulate specific neurocircuits, neurotransmitters, neuromodulators, and physiological and intracellular signaling events associated with behavioral markers that may be linked to intrusive thought. They permit unparalleled control over the external and genetic environments in ways and to degrees that are not possible in humans. Intrusive thought is an emergent property of multiple systems: emotional, cognitive, motor, and autonomic/somatic. In an animal model, one can ask specific questions about these systems and how they may be linked to, permit, or suppress intrusions. For example, how are specific connections, neuromodulators, or cell types involved in each of these systems, and how do they help form or maintain behaviors consistent with intrusive thought? Are positive versus negative valences unbalanced? Are common systems hijacked by intrusive thought, agnostic to the valence or content of the thought? Resolving these issues could be transformative for the treatment of several neuropsychiatric illnesses that are commonly characterized by intrusive thought. This chapter presents a road map for studying the neural mechanisms underlying intrusive thought using nonhuman experimental systems.
This chapter reviews different methods that can be used to examine and understand intrusive thought, beginning with behavioral methods. Common among these are self-report and diary measures of the experience, duration, and intensity of intrusive thoughts as well as self-reports of the difficulty in controlling such thoughts. These questionnaires, for the most part, have been tailored to the types of intrusions specific to a given psychiatric syndrome (e.g., flashbacks in posttraumatic stress disorder, thoughts of contamination in obsessive-compulsive disorder), which highlights the need to create a transdiagnostic self-report measure. Another common behavioral paradigm is to investigate intrusions after individuals are exposed to traumatic material, through a symptom provocation paradigm in individuals who have experienced trauma or an analog trauma (e.g., viewing a disturbing movie). Other behavioral paradigms, such as the Think/No-Think paradigm, specifically examine mechanisms of memory retrieval and suppression often thought to be disrupted in posttraumatic stress disorder.
Thereafter, it addresses paradigms for examining the neural mechanisms associated with intrusive thoughts. These approaches primarily couple behavioral techniques or paradigms with functional magnetic resonance imaging or electroencephalographic (EEG/ERP) methods. In addition to providing insights into the neural mechanisms that may underlie intrusive thoughts, these approaches may provide additional information regarding cognitive mechanisms, such as discerning whether memories are being suppressed or replaced. Discussion concludes by examining emerging approaches to the study of intrusive thinking. A main challenge is to find a method to verify that intrusive thoughts have indeed occurred. New paradigms that combine neuroimaging techniques with computational methods drawn from machine learning offer promise, as do techniques which allow intrusive thought processes to be examined as they occur during more naturalistic processing (e.g., watching a film).
Intrusive thinking, the sudden occurrence of unwanted thoughts, images, or impulses, is a frequent and natural occurrence within our stream of consciousness (Clark and Purdon 1995). Present in both clinical and nonclinical samples, the high incidence of intrusive thoughts across the population renders challenging the task to identify meaning behind their occurrence. Their presence, frequency, and content do not appear, however, to be random. Intrusive thinking manifests differently in clinical versus nonclinical populations. They may be associated with certain emotions, thus offering a glimpse into their potential adaptive nature. This chapter examines what intrusive thoughts are and what they are not. It explores how they manifest differently in clinical versus nonclinical populations and asks whether these different presentations can provide insights into their origin. It evaluates intrusions as possible manifestations of adaptations and examines intrusions linked to evolved emotions (e.g., fear, rage, jealousy, and love). Identifying the possible reasons behind intrusive thinking may help guide future treatment.
Various psychopathological symptoms share characteristics of intrusive thinking. Intrusive thoughts are part of the diagnostic criteria for posttraumatic stress disorder and obsessive-compulsive disorder but are also relevant in other psychiatric conditions, such as drug craving in addiction or rumination in depressive disorders. Intrusive thoughts must be differentiated from thought insertion observed in schizophrenia and related psychotic disorders. This chapter reviews the typical characteristics and content of intrusive thinking in the context of different psychiatric conditions and outlines current theories regarding the mechanisms of intrusive thinking.
A classic definition of intrusive thinking is “any distinct, identifiable cognitive event that is unwanted, unintended, and recurrent. It interrupts the flow of thought, interferes in task performance, is associated with negative affect, and is difficult to control” (Clark 2005:4). While easy to understand and applicable to many cases, this definition does not seem to encompass the entire spectrum of intrusions. For example, intrusive thoughts may not always be experienced as unpleasant or unwanted, and may in some situations even be adaptive. This chapter revisits the definition of intrusive thinking, by systematically considering all the circumstances in which intrusions might occur, their manifestations across health and disorders, and develops an alternative, more inclusive definition of intrusions as being “interruptive, salient, experienced mental events.” It proposes that clinical intrusive thinking differs from its nonclinical form with regard to frequency, intensity, and maladaptive reappraisal. Further, it discusses the neurocognitive processes underlying intrusive thinking and its control, including memory processes involved in action control, working memory and long-term memory encoding, retrieval, and suppression. As part of this, current methodologies used to study intrusive thinking are evaluated and areas are highlighted where more research and/or technical innovation is needed. It concludes with a discussion of the theoretical, therapeutic, and sociocultural implications of intrusive thinking and its control.
Intrusive thoughts are regular occurrences in healthy cognition. Across a variety of psychiatric conditions, however, such thoughts can become unconstructive and perseverative. Failures in computations to estimate the salience of the content of these thoughts are at least partly responsible for these clinically relevant disease symptoms. This chapter reviews neuroimaging results that show specific and related dysfunction in the calculation of salience at multiple neuroanatomically and functionally linked regions of interest, both cortically and subcortically. Transdiagnostic evidence for dysfunction in the striatum, thalamus, and prefrontal cortex is reviewed, as is a theoretical framework placing these regional findings in the context of large-scale brain networks. It is argued that changes in nodal function and network communication are signatures of a failure to properly shape predictions about the reliability and utility of external and internal stimuli, leading to maladaptive attentional capture and behavior, including intrusive thoughts.
The last decade has witnessed a marked shift of emphasis in cognitive neuroscience away from simple localization of function and toward the organization, coding, and dynamics of brain networks. This is surely a healthy evolution of our science, and the study of cognitive control has benefited from this shift, as much as any domain. However, the emphasis on brain-wide networks for cognitive control has reopened some older debates, once thought resolved, while also introducing some new ones. This chapter focuses on four questions viewed as unresolved and fundamental because one’s particular answer to them commits to some basic theoretical differences regarding cognitive control function: Are there one, many, or any networks whose primary function is best described as cognitive control? Are the networks supporting cognitive control in the brain “hub-like” or “hierarchical” in their intrinsic and extrinsic organization? Are the networks for cognitive control modulatory or transmissive in the pathway from thought to action? Does controllability apply at the level of cognitive function or brain state? Each question is defined and relevant background is presented that could inform a resolution.
Why do some thoughts feel involuntary and intrusive? When should we hold someone responsible for their actions and thoughts when they all have some basis in the brain? Are we truly free agents when we are bounded by shared values and culture? This chapter presents a framework for how our consciousness of our own intentions and emotions allows us to form causal narratives about ourselves and the world. These narratives determine our sense of agency, and we ascribe responsibility correctly depending on the extent to which one is capable of forming culturally appropriate narratives. Different ways of characterizing consciousness are analyzed, with a focus on one that may prove most useful within the context of understanding individual agency. A variant of the higher-order view of consciousness is advocated that allows us to form causal, albeit imperfect, narratives about ourselves. However, it is because of these imperfect narratives that our understanding of agency and responsibility is formed. Thus, understanding how these narratives come about is an important first step to understanding agency and how some thoughts are considered involuntary and intrusive. Implications of this framework are discussed using examples from mental illnesses, addiction, suicide, and racism.
This chapter explores how intrusive experiences may occur at a systems level from psychological, computational, neurobiological, and physiological perspectives. A general scheme is proposed of the essential elements of an intrusive experience, and where in this scheme dysregulation could occur to increase the likelihood of an intrusive experience. It also considers a range of psychological and mathematical models that have been applied to explain how intrusions may ultimately happen, some of which are more closely integrated into neurobiological systems than others. These include a Bayesian model of active inference, integrated psychological and physiological models of interoception, and psychological and neurobiological models of working memory and associative learning and their relevance to concepts of flexibility and stability.
Common across psychological disorders, intrusive, emotional mental images are sensory-perceptual representations that intrude involuntarily into the mind. Mental health treatments typically focus on entire disorders with multiple symptoms. This chapter suggests focusing on core clinical symptoms (i.e., intrusive imagery). Existing psychological therapy techniques (e.g., imagery rescripting) are promising, but underlying treatment mechanisms need to be better understood.
Precise treatments and preventions are required. Using the example of psychological trauma, this chapter argues that psychological interventions can be developed in the laboratory: effective experimental analogues of trauma can generate intrusions so that putative interventions that modulate intrusions can be explored at various mechanistic levels (e.g., molecular, cognitive, social). Examples of targeting “new” (i.e., Day 1 of the traumatic event) memories include a simple cognitive interference intervention that holds promise for preventing intrusive images after trauma (a behavioral protocol including Tetris game play). This intervention specifically targets intrusive involuntary memories while leaving voluntary memory intact. Work on targeting “old” (as of Day 2) memories is at an earlier stage. Research on reconsolidation update mechanisms appears valuable in reducing older trauma memories via interference interventions, again with a behavioral task interference technique. To understand mechanisms across different levels (e.g., molecular, cognitive, or social), mathematical models can aid the identification of causal mechanisms involved in memory formation. Questions are posed to instigate discussion of future science-driven psychological interventions for intrusive images.
Intrusive thoughts are features of numerous psychiatric disorders. They vary widely in form, duration, frequency, and severity. They are associated with disorders with widely differing pathophysiology, and they are likely to respond to different pharmacological treatments. It is possible that intrusive thoughts represent a cross-diagnostic symptom that can be a pharmacological target in their own right, separate from the associated disorder. This chapter considers the challenges in studying intrusive thoughts as a separate entity. It examines intrusive thoughts that are symptoms of several different psychiatric disorders and reviews the medications that have been used to treat them. It holds that relatively little is known about the effects of psychiatric medications on intrusive thoughts, either within disorders (separate from other symptoms) or across disorders. A wide range of medications is used to treat intrusive thoughts that target different neurotransmitter systems. In addition to the psychopharmacological armamentarium, new, single dose treatments (e.g., ketamine, psilocybin, and MDMA) have emerged that may specifically address intrusive thoughts across the psychiatric spectrum. In conclusion, possible directions are discussed for identifying subcategories of intrusive thoughts that could advance research and treatment in this area.
Intrusive thinking is a core feature in multiple psychiatric diseases, including obsessive-compulsive disorder (OCD), posttraumatic stress disorder (PTSD), substance use disorder (SUD), and Tourette syndrome. These diseases are not only bound by intrusive thinking, they also share similar disruptions in the functional architecture of the brain, including frontal-striatal-thalamic circuitry which is involved in salience attribution and shifting attention. As more is learned about the neural circuit dysfunctions involved in the initiation, maintenance, and attention to intrusive thoughts, it may become possible to develop noninvasive neuromodulation approaches to attenuate the presence of these thoughts or the morbidity associated with their existence in individuals. This chapter focuses on transcranial magnetic stimulation (TMS) as a tool to induce causal change in behavior, cortical excitability, and frontal-striatal activity. An overview is provided of the cortical and subcortical areas that are often implicated in intrusive thinking, using examples from Tourette syndrome, OCD, PTSD, and SUD. The hypotheses presented can be generalized past TMS to other invasive and noninvasive forms of neuromodulation. In conclusion, key questions are posed to move the field forward.
This chapter provides a framework for developing interventions that specifically target intrusive events. It describes the challenges in defining intrusive thoughts and the difficulty in distinguishing normal processes of cognition and emotion from indicators of dysfunction, defined from practical, neurobiological, or cultural points of view. Throughout, the term intrusive events is used to encompass both thoughts and images that become intrusive. Examples are explored as they occur in different psychiatric disorders to demonstrate their variance in form, frequency, and controllability. Treatment modalities that have been used to alleviate intrusive events in different psychiatric disorders are reviewed, including behavioral, pharmacological, and emerging electromagnetic brain interventions. Two clinical vignettes illustrate the nature and severity of intrusive events in patient populations as well as the complex, multidimensional nature of the clinical reality. Ways of measuring intrusive events are examined and deconstructed into components (e.g., sensory, motor, and cognitive features). By examining intrusive events across diagnostic categories, common basic biobehavioral processes may be revealed which, in turn, could facilitate the study of neural processes underlying the behaviors. A model of cognitive and emotional decision making is presented to provide a basis for understanding and studying intrusive events. Examples of how the model might account for the “failure modes” in intrusive events are used to formulate testable hypotheses, and future interventions that combine multiple treatment modalities are considered. The chapter concludes with a discussion of the broader cultural context of intrusive events.