The concept of a mental disorder is one of those things that seems simple at first glance, but turns out to be very complex and quite tricky (similar to clearly defining “consciousness,” “stress,” or “personality”). Any extreme variation in your thoughts, feelings, or behaviours is not a mental disorder. For instance, severe anxiety before a test, sadness after the loss of a loved one, or a night of excessive alcohol consumption—although unpleasant—is not necessarily pathological. Similarly, a persistent pattern of deviating from the norm does not qualify a person for a mental disorder. If it did, we would diagnose mental disorders in the most creative and visionary people—anyone whose ideas deviate from those around them.

So what is a mental disorder? Perhaps surprisingly, there is not universal agreement on a precise definition of the term “mental disorder.” However, there is general agreement that a mental disorder can be defined as a persistent disturbance or dysfunction in behaviour, thoughts, or emotions that causes significant distress or impairment (Stein et al., 2010; Wakefield, 2007). One way to think about mental disorders is as dysfunctions or deficits in the normal human psychological processes you have learned about throughout this textbook. People with mental disorders have problems with their perception, memory, learning, emotion, motivation, thinking, and social processes. You might ask: But this is still a broad definition, so what kinds of disturbances “count” as mental disorders? How long must they last to be considered “persistent?” And how much distress or impairment is required? These are all hotly debated questions in the field. They have been for many years, and likely will be for years to come (as discussed in more detail later).

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Historically speaking, there are reports of people acting strangely or reporting bizarre thoughts or emotions since ancient times. Until fairly recently, such difficulties were conceptualized as the result of religious or supernatural forces. In some cultures, psychopathology is still interpreted as possession by spirits or demons, as enchantment by a witch or shaman, or as God’s punishment for wrongdoing. In many societies, including our own, people with psychological disorders have been feared and ridiculed, and often treated as criminals: punished, imprisoned, or put to death for their “crime” of deviating from the normal.

Over the past 200 years, these ways of looking at psychological abnormalities have largely been replaced in most parts of the world by a medical model, in which abnormal psychological experiences are conceptualized as illnesses that, like physical illnesses, have biological and environmental causes, defined symptoms, and possible cures. Conceptualizing abnormal thoughts and behaviours as illness suggests that a first step is to determine the nature of the problem through diagnosis.

In diagnosis, clinicians seek to determine the nature of a person’s mental disorder by assessing signs (objectively observed indicators of a disorder) and symptoms (subjectively reported behaviours, thoughts, and emotions) that suggest an underlying illness. So, for example, just as a self-reported fever, sniffles, and cough are symptoms of a cold, Virginia Woolf’s extreme moods, alternating between despondency and wild euphoria, can be seen as symptoms of her bipolar disorder. It is important to note the differences among three related general medical and classification terms:

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Importantly, knowing that a disorder is present (i.e., diagnosed) does not necessarily mean that we know the underlying disease process in the body that gives rise to the signs and symptoms of the disorder.

Viewing mental disorders as medical problems reminds us that people who are suffering deserve care and treatment, not condemnation. Nevertheless, there are some criticisms of the medical model. Some psychologists argue that it is inappropriate to use clients’ subjective self-report, rather than physical tests of pathology (as in other areas of medical diagnostics), to determine underlying illness. Others argue that the model often “medicalizes” or “pathologizes” normal human behaviour. For instance, extreme sadness can be considered to be an illness called major depressive disorder; extreme shyness can be diagnosed as an illness called social anxiety disorder; and trouble concentrating in school is called attention-deficit/hyperactivity disorder. Although there are some valid concerns about the current method of defining and classifying mental disorders, it inarguably is a huge advance over older alternatives, such as viewing mental disorders as the work of witchcraft or as punishment for sin. Moreover, psychologists keep these concerns in mind as they work to improve the diagnostic procedures.

So how is the medical model used to classify the wide range of abnormal behaviours that occur among humans? Psychologists, psychiatrists (physicians concerned with the study and treatment of mental disorders) and most other people working in the area of mental disorders use a standardized system for classifying mental disorders. There are currently two established systems for classifying mental disorders: The International Classification of Diseases (ICD-10) produced by the World Health Organization, and the Diagnostic and Statistical Manual of Mental Disorders (DSM) produced by the American Psychiatric Association (APA). Since the DSM tends to be the classification used most widely in North America, it is the one we shall focus on. The DSM is a classification system that describes the features used to diagnose each recognized mental disorder and indicates how the disorder can be distinguished from other, similar problems. Each disorder is named and classified as a distinct illness. The initial version of the DSM, published in 1952, and its revision, DSM–II, published in 1968, provided a common language for talking about disorders. This was a major advance in the study of mental disorders; however, the diagnostic criteria listed in these early volumes were quite vague and based on thin theoretical assumptions. For instance, people who were extremely depressed or anxious for long periods of time might be given the general diagnosis of “neurosis reaction.”

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The next two editions of the DSM (DSM–III, published in 1980 and DSM–IV, published in 1994) moved from vague descriptions of disorders to very detailed lists of symptoms (or diagnostic criteria) that had to be present in order for a disorder to be diagnosed. For instance, in addition to being extremely sad or depressed (for at least 2 weeks), a person must have at least five of nine agreed upon symptoms of depression (e.g., diminished interest in normally enjoyable activities, significant weight loss or gain, significantly increased or decreased sleep, loss of energy, feelings of worthlessness or guilt, trouble concentrating). The use of these detailed lists of symptoms for each of more than 200 disorders listed led to a dramatic increase in the reliability, or consistency, in diagnosing mental disorders. Two clinicians interviewing the same individual were now much more likely to agree on what mental disorders were present, greatly increasing the credibility of the diagnostic process (and the fields of psychiatry and clinical psychology).

In May, 2013, the American Psychiatric Association released an updated manual: DSM–5. The DSM–5 describes 22 major categories containing more than 200 different mental disorders (see TABLE 15.1). Along with the disorders listed in these 22 categories, the DSM–5 describes conditions that may be included as formal disorders, but that, for now, require additional research. In addition, there is a section devoted to cultural considerations in diagnosing mental disorders. Why the switch from Roman to Arabic numerals? The hope is that with more rapid advances in our understanding of mental disorders, rather than wait another 20 years to update the DSM, we can make revisions as we learn more (DSM–5.1, 5.2, 5.3, and so on).

Each of the 22 chapters in the main body of the DSM–5 lists the specific criteria that must be met in order for a person to be diagnosed with each disorder. Approximately 1 in 5 Canadians will personally experience a mental disorder in their lifetime (Canadian Mental Health Association, n.d. 1). And, most of those with a mental disorder (greater than 80 percent) report comorbidity, which refers to the co-occurrence of two or more disorders in a single individual (Gadermann et al., 2012).

The medical model of mental disorder suggests that knowing a person’s diagnosis is useful because any given category of mental illness is likely to have a distinctive cause. In other words, just as different viruses, bacteria, or genetic abnormalities cause different physical illnesses, so a specifiable pattern of causes (or etiology) may exist for different psychological disorders. The medical model also suggests that each category of mental disorder is likely to have a common prognosis, a typical course over time and susceptibility to treatment and cure. Unfortunately, this basic medical model is usually an oversimplification; it is rarely useful to focus on a single cause that is internal to the person and that suggests a single cure.

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To understand what factors might cause mental disorders, most psychologists take an integrated biopsychosocial perspective that explains mental disorders as the result of interactions among biological, psychological, and social factors. On the biological side, the focus is on genetic and epigenetic influences (see Figure 3.23 in the Neuroscience and Behaviour chapter), biochemical imbalances, and abnormalities in brain structure and function. The psychological perspective focuses on maladaptive learning and coping, cognitive biases, dysfunctional attitudes, and interpersonal problems. Social factors include poor socialization, stressful life experiences, and cultural and social inequities. The complexity of causation suggests that different individuals can experience a similar psychological disorder (e.g., depression) for different reasons. A person might fall into depression as a result of biological causes (e.g., genetics, hormones), psychological causes (e.g., faulty beliefs, hopelessness, poor strategies for coping with loss), environmental causes (e.g., stress or loneliness), or more likely as a result of some combination of these factors. And, of course, multiple causes mean there may not be one single cure.

The observation that most disorders have both internal (biological and psychological) and external (environmental) causes has given rise to a theory known as the diathesis-stress model, which suggests that a person may be predisposed for a psychological disorder that remains unexpressed until triggered by stress. The diathesis is the internal predisposition and the stress is the external trigger. For example, most people were able to cope with their strong emotional reactions to the terrorist attack of September 11, 2001. However, for some who had a predisposition to negative emotions, the horror of the events may have overwhelmed their ability to cope, thereby precipitating a psychological disorder. Although diatheses can be inherited, it is important to remember that heritability is not destiny. A person who inherits a diathesis may never encounter the precipitating stress, whereas someone with little genetic propensity to a disorder may come to suffer from it given the right pattern of stress. The tendency to oversimplify mental disorders by attributing them to single, internal causes is nowhere more evident than in the interpretation of the role of the brain in psychological disorders. Brain scans of people with and without disorders can give rise to an unusually strong impression that psychological problems are internal and permanent, inevitable, and even untreatable. Brain influences and processes are fundamentally important for knowing the full story of psychological disorders, but are not the only chapter in that story.

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Although the DSM provides a useful framework for classifying disorders, there has been a growing concern over the fact that the findings from scientific research on the biopsychosocial factors that appear to cause psychopathology do not map neatly onto individual DSM diagnoses. Succinctly characterizing the current state of affairs, Thomas R. Insel, Director of the American National Institute of Mental Health (NIMH; the primary funder of research on mental disorders in the United States), noted that although many people describe the DSM as a bible, it is more accurate to think of it like a dictionary that provides labels and current definitions: “People think that everything has to match DSM criteria, but you know what? Biology never read that book” (Insel, quoted in Belluck & Carey, 2013, p. A13). In order to better understand what actually causes mental disorders, researchers at the NIMH have proposed a new framework for thinking about mental disorders focused not on the currently defined DSM categories of disorders, but on the more basic biological, cognitive, and behavioural constructs that are believed to be the building blocks of mental disorders. This new system is called the Research Domain Criteria Project (RDoC), a new initiative that aims to guide the classification and understanding of mental disorders by revealing the basic processes that give rise to them. The RDoC is not intended to immediately replace the DSM, but to inform future revisions to it in the coming years (see The Real World box).

Using the RDoC, researchers study the causes of abnormal functioning by focusing on biological factors from genes to cells to brain circuits; psychological domains, such as learning, attention, memory; and various social processes and behaviour (see TABLE 15.2 for a list of domains). The hope is that the RDoC approach will lead to more progress in understanding the underlying causes of mental disorders than does a focus on the traditional labels, and will also reveal links between disorders that were not previously suspected. The long-term goal is to better understand what abnormalities cause different disorders, and to classify disorders based on those underlying causes, rather than on observed symptoms. This approach would bring the study of mental disorders in line with the study of other medical disorders. For example, if you are experiencing chest pain, severe headaches, fatigue, and difficulty breathing, it is unlikely that you are experiencing four separate disorders (chest pain disorder, headache disorder, etc.). Instead, we now know that these are all symptoms of an underlying disease process called hypertension. The RDoC approach similarly aims to shift the focus away from classifying based on surface symptoms and toward an understanding of the processes that give rise to disordered behaviour. For instance, rather than studying cocaine addiction as a distinct disorder, from an RDoC perspective researchers might try to understand what causes abnormalities in “responsiveness to reward,” a factor seen in those with excessive cocaine use as well as those with other addictive behaviours. Indeed, recent research has shown that variations in a gene (DRD2) that codes for dopamine receptors are associated with abnormalities in connectivity between parts of the frontal lobe and the striatum (described in the Neuroscience and Behaviour chapter). This lack of connectivity is, in turn, related to the impulsiveness and responsiveness to rewards associated with a range of addictive behaviour disorders (Buckholtz & Meyer-Lindenberg, 2012). This may help explain why some people seem to be vulnerable to different kinds of addiction and have trouble inhibiting their reward-seeking behaviour. Importantly, understanding what processes cause problems like addiction will help us to develop more effective treatments, a topic we address in more detail in the next chapter.

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You might have noticed that the list of domains in Table 15.2 looks like a slightly more detailed version of the table of contents for this textbook! The RDoC approach has an overall emphasis on neuroscience (Chapter 3), and specific focuses on abnormalities in emotional and motivational systems (Chapters 8), cognitive systems such as memory (Chapter 6), learning (Chapter 7), language and cognition (Chapter 9), social processes (Chapter 13), and stress and arousal (Chapter 14). From the RDoC perspective, mental disorders can be thought of as the result of abnormalities or dysfunctions in normal psychological processes. By learning about many of these processes in this textbook, you will likely have a good understanding of new definitions of mental disorders as they are developed in the years ahead.

An important complication in the diagnosis and classification of psychological disorders is the effect of labelling. Psychiatric labels can have negative consequences because many carry the baggage of negative stereotypes and stigma, such as the idea that mental disorder is a sign of personal weakness or the idea that psychiatric patients are dangerous. The stigma associated with mental disorders may explain why most people with diagnosable psychological disorders (approximately 60 percent) do not seek treatment (Kessler, Demler, et al., 2005; Wang, Berglund, et al., 2005).

Unfortunately, educating people about mental disorders does not dispel the stigma borne by those with these conditions (Phelan et al., 1997). In fact, expectations created by psychiatric labels can sometimes even compromise the judgment of mental health professionals (Garb, 1998; Langer & Abelson, 1974; Temerlin & Trousdale, 1969). In a classic demonstration of this phenomenon, psychologist David Rosenhan and six associates reported to different mental hospitals complaining of “hearing voices,” a symptom sometimes found in people with schizophrenia. Each was admitted to a hospital, and each promptly reported that the symptom had ceased. Even so, hospital staff were reluctant to identify these people as normal: It took an average of 19 days for these “patients” to secure their release, and even then they were released with the diagnosis of “schizophrenia in remission” (Rosenhan, 1973). Apparently, once hospital staff had labelled these patients as having a psychological disease, the label stuck.

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These effects of labelling are particularly disturbing in light of evidence that the hospitalization of people with mental disorders is seldom necessary. One set of studies followed the lives of patients who were thought to be too dangerous to release and therefore had been kept in the back wards of institutions for years. Their release resulted in no harm to the community (Harding et al., 1987), and further studies have shown that those with a mental disorder are no more likely to be violent than those without a disorder (Elbogen & Johnson, 2009; Monahan, 1992).

Labelling may even affect how labelled individuals view themselves; persons given such a label may come to view themselves not just as mentally disordered, but as hopeless or worthless. Such a view may cause them to develop an attitude of defeat and, as a result, to fail to work toward their own recovery. As one small step toward counteracting such consequences, clinicians have adopted the important practice of applying labels to the disorder and not to the person with the disorder. For example, an individual might be described as “a person with schizophrenia,” not as “a schizophrenic.” You will notice that we follow this convention in the textbook.