The concept of a mental disorder seems simple at first glance, but it 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 behaviors 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 are not necessarily pathological. Similarly, a persistent pattern of deviating from the norm does not necessarily qualify a person for the diagnosis of 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 no 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 behavior, 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 book. 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.

Since ancient times, there have been reports of people acting strangely or reporting bizarre thoughts or emotions. Until fairly recently, such difficulties were 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 they were treated as criminals who were punished, imprisoned, or put to death for their “crime” of deviating from the normal.

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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 behaviors 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 behaviors, thoughts, and emotions) that suggest an underlying illness. So, for example, just as self-reported 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:

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 behavior. 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 can be attention-deficit/hyperactivity disorder. Although there are some valid concerns about the current method of defining and classifying mental disorders, the medical model inarguably is a huge advance over older alternatives, such as viewing mental disorders as the work of witchcraft or as punishment for sin.

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So how is the medical model used to classify the wide range of abnormal behaviors that occur among humans? Most people working in the area of mental disorders use a standardized system for classifying mental disorders called the Diagnostic and Statistical Manual of Mental Disorders (DSM), 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, 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.

Over the decades, revised editions of the DSM have 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 the newest, fifth edition of the DSM, the DSM–5. The DSM–5 describes 22 major categories containing more than 200 different mental disorders, along with the specific criteria that must be met in order for a person to be diagnosed with that disorder (see TABLE 14.1). In addition, there is a section devoted to cultural considerations in diagnosing mental disorders.

Studies of large, representative samples of the U.S. population reveal that approximately half of Americans report experiencing at least one mental disorder during the course of their lives (Kessler, Berglund, et al., 2005). And, most of those with a mental disorder (greater than 80%) 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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Instead, 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, 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 mental 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 a single cure.

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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 the person’s ability to cope, thereby precipitating a psychological disorder. Although diatheses can be inherited, it’s 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 still come to suffer from such a disorder given the right pattern of stress.

Although the DSM provides a useful framework for classifying disorders, there has been a growing concern that the findings from scientific research on the factors that cause psychopathology do not map neatly onto individual DSM diagnoses. In order to better understand what actually causes mental disorders, researchers at the National Institutes of Mental Health (NIMH) have proposed a new framework for thinking about mental disorders, one that is focused not on the currently defined DSM categories of disorders, but on the basic biological, cognitive, and behavioral processes (or “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 intended not to immediately replace the DSM but to inform future revisions to it in the coming years. Using the RDoC, researchers focus on biological domains, such as arousal and sleep patterns; and psychological domains, such as learning, attention, and memory; and social domains, such as attachment and self-perception (see TABLE 14.2 for a list of domains). Each of these domains can be approached by studying various “units of analysis”—from genes, to cells, to behavior, as shown in the columns of the table.

Through the RDoC approach, the NIMH would like to shift researchers away from studying currently defined DSM categories and toward the study of the dimensional biopsychosocial processes believed, at the extreme end of the continuum, to lead to mental disorders. 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 behavior. 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 behaviors. 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 Behavior chapter). This lack of connectivity is, in turn, related to the impulsiveness and responsiveness to rewards associated with a range of addictive behavior disorders (Buckholtz & Meyer-Lindenberg, 2012). This may help explain why some people seem to have addictive personalities in which they have trouble inhibiting their reward-seeking behavior, which in turn could predispose a person to develop drug addiction. 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 notice that the list of domains in Table 14.2 looks like a slightly more detailed version of the table of contents for this book! The RDoC approach has an overall emphasis on neuroscience (Chapter 3), with specific focuses on abnormalities in emotional and motivational systems (Chapter 8), cognitive systems such as memory (Chapter 6), learning (Chapter 7), language and cognition (Chapter 9), social processes (Chapter 12), and stress and arousal (Chapter 13). 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 book, 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 labeling. Psychiatric labels can have negative consequences because many labels 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%) 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, researchers 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 labeled these patients as having a psychological disease, the label stuck.

Labeling may even affect how labeled 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’ll notice that we follow this convention in the text.