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be described in a dimensional manner in terms of a certain number of degrees. However, at a critical point, the water turns to steam, which is a categorically different state from water. Likewise, a reduction in temperature changes water into a different categorical state—ice. The question for the study of psychopathological disorders is to determine the underlying dimensional changes that are associated with categorical-like transformations leading to a disordered state. Further, different underlying processes may actually allow for the presence of more than one disordered state at the same time.

      Comorbidity, Internalizing Disorders, and Externalizing Disorders

      Technically, when an individual is seen to have more than one disorder at the same time, the disorders are referred to as comorbid. In the National Comorbidity Survey, a large number of individuals with one disorder were found to have one or more additional diagnoses (Kessler et al., 1994). For example, individuals with generalized anxiety disorder will often also show symptoms of depression. Further, these two disorders have overlapping genetic and environmental risk factors (Kendler, Neale, Kessler, Heath, & Eaves, 1992). The number of diagnoses found in the National Comorbidity Survey was associated with the severity of the symptoms. This has suggested to researchers that there exists a general underlying vulnerability to psychopathology that may be independent of the particular symptoms expressed (Pittenger & Etkin, 2008).

      comorbid: descriptive term used when an individual has more than one disorder at the same time

      internalizing disorders: disorders that are experienced internally such as anxiety and depression

      externalizing disorders: disorders that are manifested in the external world by the person’s behavior, such as conduct disorder (CD), antisocial personality disorder, and other behavior-based disorders

      A related approach is to consider which disorders co-occur with one another. In general, two clusters have been found. The first is referred to as internalizing disorders. The focus of these disorders is the inner world of the person, and they include anxiety and depression. The second cluster is referred to as externalizing disorders. The behavioral focus of these disorders is the external environment of the person. These disorders include conduct disorder, oppositional defiant disorder, antisocial personality disorder, substance use disorder, and in some studies attention deficit/hyperactivity disorder (ADHD). These studies of comorbidity clusters have led scientists to search for common factors such as genetics, brain processes, and environmental risk profiles that might be associated with each cluster. Overall, research has supported the idea that mental disorders can be clustered and that it is possible to identify underlying risk factors (Kendler, et al., 2011).

      Given these new perspectives, it is not surprising that with new scientific discoveries the field of mental illness is in flux. In this section, I want to describe the nature of some of the current considerations of how we should approach the field of psychopathology from these larger perspectives. In later chapters of this book, I will describe specific approaches in greater detail.

      Utilizing Neuroscience Methods in Diagnosis and Treatment

      As noted, there has been a push to find more objective markers that can be used in the diagnosis and treatment of mental disorders using neuroscience research. With the advent of the various levels of analysis available to neuroscientists including brain imaging, genetics, biochemical and electrophysiological processes, brain networks, behavior, and experience, a variety of researchers have sought to describe cognitive, emotional, and motor processes in both health and illness. This has resulted in a better articulation of what underlies these processes.

      One such underlying process is memory. It is possible to describe its underlying process including specific brain areas such as the hippocampus, the brain networks involving memory, and the biochemical and structural changes among neurons as new information is retained. With this knowledge, it is also possible to explore psychopathological conditions such as amnesia or delusions that involve the memory system.

      Figure 4.5 Reward System of the Brain

      Another example is the reward system. Humans seek rewards from a variety of sources, including food, sex, power, acclaim, and affiliation, as well as drugs. A number of studies show that particular brain structures, especially the nucleus accumbens part of the ventral striatum, are influenced by an increase in dopamine during a reward (see Figure 4.5). In fact, all addictive drugs result in dopamine release in the nucleus accumbens (Pittenger & Etkin, 2008). Individuals with alcoholism show greater activation to alcohol-related cues in the nucleus accumbens and the anterior thalamus. The activation of the nucleus accumbens also correlates with the degree of craving. One approach involving the reward system is to note its involvement in active reward processes such as those seen in addiction or mania as well as those disorders in which reward is reduced such as depression or schizophrenia (Russo & Nestler, 2013).

      reward system: particular brain structures, especially the nucleus accumbens part of the ventral striatum, influenced by an increase in dopamine during a reward

      Since the beginning of the twenty-first century, a number of researchers and clinicians have asked whether it would be possible to use neuroscience approaches to classify mental illness and inform its treatment (Cuthbert & Insel, 2010; Halligan & David, 2001; Hyman, 2007, 2010; Insel, 2009; G. Miller, 2010; Sanislow et al., 2010). Part of this desire stems from the fact that not all individuals with depression, for example, report the same symptoms. This suggests to some researchers that there might be different underlying brain processes involved in what appears as a single disorder. By knowing the underlying processes involved in a particular disorder, it would be possible to create a treatment that was specific to a given individual.

      Neuroscience perspectives can also help validate theoretical constructs used in a variety of theoretical orientations. For example, Carhart-Harris and Friston (2010) examined the relationship between brain network processes and Freudian constructs. Likewise, DeRubeis, Siegle, and Hollon (2008) examined the different pathways of treatment for depression found in cognitive therapy versus medication. These researchers suggested that cognitive therapy works through a top-down approach by increasing higher cortical functioning associated with the frontal lobes, whereas medication works in a more bottom-up approach by decreasing excessive emotional responsiveness associated with the amygdala.

      National Institute of Mental Health (NIMH): agency of the U.S. government that advances the understanding and treatment of mental disorders

      One large organization emphasizing the utilization of neuroscience information to understand mental illness is the National Institute of Mental Health (NIMH) in the United States (Insel, 2009). Through its research mission, NIMH developed four major objectives:

      The plan calls for research that will (1) define the pathophysiology of disorders from genes to behavior, (2) map the trajectory of illness to determine when, where, and how to intervene to preempt disability, (3) develop new interventions based on a personalized approach to the diverse needs and circumstances of people with mental illnesses, and (4) strengthen the public health impact of NIMH-supported research by focusing on dissemination science and disparities in care. (Insel, 2009, p. 128)

      Former director of the National Institute on Drug Abuse (NIDA), Dr. Alan I. Leshner, discusses PET scans showing brain activity before and after use of the drug MDMA (ecstasy).

      Michael Smith/Staff/Hulton Archive/Getty Images

      As can be seen, the objectives are designed to identify the manner in which brain processes are involved in a specific disorder, to better describe the course of a mental disorder including when the first signs appear—even if abnormal processes are not yet seen—so as to use this knowledge to create a treatment related to a given individual, and

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