Читать книгу Abnormal Psychology - William J. Ray - Страница 73

The past 40 years has brought forth new technologies that allow us to study human behavior and experience in ways not previously possible. As you will see with many of the techniques described in this chapter, sampling brain processes or genetic material is basically simple and painless for the people involved. In terms of psychopathology, by using brain imaging techniques it is possible to see how individuals with a particular mental disorder perform cognitive and emotional tasks differently from those without the disorder. We can also examine genetic differences between those with a certain disorder and those who do not show the signs and symptoms of the disorder. Further, to understand the brain and genetic levels, it is important to consider the role that evolution has played. These three approaches will be emphasized in this chapter.

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

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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.