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      Modern brain imaging techniques help researchers discover how mental disorders appear in the brain.

      Ben Edwards/The Image Bank/Getty Images

      One word of warning before we continue—currently, we have no neuroscience technique that can definitively diagnose a given individual in terms of mental disorders. What we can say is that a group of individuals with a particular disorder appear to differ on certain measures compared to a group of individuals without the disorder. Even those with the same disorder may show differences in how the disorder is manifested.

      To understand mental illness as a brain disease, we need methods for showing how the brain is involved in psychopathology (Andreasen, 2001). Within the past four decades, a variety of research techniques have been developed or significantly improved that allow us to better specify the nature of mental disorders from the standpoint of the brain. In this quest, there has been a strong emphasis on brain imaging, genetics, and an evolutionary perspective. In general, these approaches have allowed researchers to study individuals with mental disorders on a number of levels simultaneously.

      Historically, what we now consider to be neuroscience approaches to psychopathology were limited. For example, Broca in the 1800s needed to wait until his patients died before he could study the nature of their brains. In the early part of the twentieth century, work with animals was the major way of understanding how the various structures of the brain influenced behavior. Some scholars such as Carl Jung added EDA to reaction time research. Jung used the word association test developed by Wilhelm Wundt to better understand psychopathology and how individuals with different disorders process cognitive and emotional information. The second part of the twentieth century expanded a tradition that used psychophysiological measures such as electroencephalography (EEG) and EDA to study psychopathology. In the current century, a variety of noninvasive techniques allow researchers and clinicians to obtain a better view of how the brain and other physiological systems function in psychopathology (see Raichle, 2010, 2015, for overviews). These will be reviewed in this chapter.

      One common conviction of neuroscientists is that there is something unusual about the human brain that leads to our abilities to perform a variety of tasks (Northcutt & Kaas, 1995; Preuss & Kaas, 1999). The human brain has been estimated to contain 86 billion neurons and more than 100,000 kilometers of interconnections (Hofman, 2001; Goldstone, Pestilli, & Börner, 2015). Estimates in mammals suggest that a given neuron would directly connect to at least 500 other neurons and probably more. This, in turn, would suggest there are 50 trillion different connections in the human brain!

      A 1-year-old infant has more neurons than she will have throughout her life.

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      Regardless of how exact this estimate may be, the conclusion is that the human brain has an extremely complex set of networks. Neurons created before birth follow chemical or other pathways in the brain to create the necessary connections to allow for vision, hearing, and other processes. We also know that neurons are also created in humans after birth. A 1-year-old infant has more neurons than she will have throughout her life. After that, neurons are gained and lost depending on use. The genetic and brain mechanisms that create and remove neurons from the developing brain play an important role in the development of mental disorders. Let us now turn to the brain itself.

      Brain Anatomy, Neurons, and Neurotransmitters

      In this section, I will introduce you to the basic mechanism of the brain, the neuron. Over millions and even billions of years of evolution, the neuron has served as the basic building block of many organisms ranging from jellyfish to humans. First, let’s briefly examine some basic descriptions of brain anatomy.

      Figure 2.3 Terms Used to Describe Location of Brain Areas

      A Quick Review of Brain Anatomy and Function

      Let’s begin with some simple terms. Structures closer to the front of the brain are referred to as anterior, whereas those closer to the back are called posterior. You will also see the terms dorsal, which is toward the back side, and ventral, which is toward the belly side (see Figure 2.3).

      The brain appears symmetrical from the top with left and right hemispheres. Structures closer to the midline dividing the left and right hemispheres are referred to as medial, whereas those farther away from the midline are called lateral.

      Brain areas can be described both in terms of location and function. Looking at the left hemisphere from the side, we can describe four lobes of the brain (see Figure 2.4). In addition to structure, we can also describe areas of the brain that are associated with different functions (see Figure 2.5). The frontal lobe is located at the front of the cortex. The frontal lobe is involved in planning, higher-order cognitive processes such as thinking and problem solving, as well as moral and social judgments.

      Figure 2.4 The Left Hemisphere of the Brain From the Left Side Noting the Major Anatomical Structures

      There is a cavity referred to as the central sulcus that separates the frontal lobe from the parietal lobe. The brain area behind the central sulcus receives sensory information from our body including the experience of touch. The area in front of the central sulcus allows the muscles of our bodies to make movements such as picking up a glass. The parietal lobe, which is toward the back and at the top of the cortex, is involved in spatial processes such as knowing where you are in space and performing spatial problems. The occipital lobe is located near the back of the brain and toward the bottom. The occipital lobe is involved with the processing of visual information and receives information from our eyes. Below the frontal and parietal lobes is the temporal lobe. Looking at the brain, you can see that the frontal and temporal lobes are separated by a deep groove, which is called the Sylvian fissure. The temporal lobe receives information from our ears and is involved in hearing as well as aspects of language. Other parts of the temporal lobe are involved in the naming of objects from visual information processed in the occipital lobes. Let us now turn to the manner in which information

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