Читать книгу Abnormal Psychology - William J. Ray - Страница 72

 2.1 Explain why neuroscience, genetics, and an evolutionary perspective are increasingly important in understanding psychopathology.

 2.2 Describe how information is communicated within the human brain.

 2.3 Describe the major techniques used to view the human brain at work, and their related ethical implications.

 2.4 Explain what brain networks are and how they influence human behavior.

 2.5 Explain the function of genes, epigenetics, and endophenotypes.

 2.6 Ask critical questions about psychopathology from an evolutionary perspective.

The neuroscientist V. S. Ramachandran (1998) told about an individual, David, who came to see him at the medical center in San Diego, California. David appeared completely normal. He had no problems with memory, engaged easily in conversation, expressed emotions, and otherwise appeared as anyone you might meet any day. However, he did one very puzzling thing. When he saw his mother in any context, he would say, “That woman looks exactly like my mother, but she is not my mother!”

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As a clinician, how might you understand this? You might ask if this was some type of psychosis in which David had the delusion that his mother was not his mother. However, David showed no other signs of disorganization or problems with functioning. You might also ask if David had any type of emotional conflict with his mother. The answer was no. After more information gathering, it was discovered that David, at times, also thought his father was not his real father. Additional information revealed that David did indeed experience his parents as his parents when talking to them on the phone.

Figure 2.1 The Fusiform Face Area in the Brain, Activated When Humans Look at Faces

The formal name for this condition is Capgras syndrome, named after the physician who first described the symptoms in the 1920s. However, the mechanisms involved are still not clear today. Since David had previously had a motorcycle accident, it was possible that normal brain processes were not functioning correctly. In order to understand David, Ramachandran asked himself what was missing in David’s experience of his mother. His answer was that there was no emotional response.

The normal emotional response to seeing someone like our parents occurs as follows: Our visual system gives us the experience of seeing the person. In humans, one particular part of the temporal lobe is sensitive to seeing faces, the fusiform face area (FFA; see Figure 2.1).

In turn, this information goes to a variety of areas including the limbic system, which is involved in emotional processing. One particular structure, the amygdala, is involved in perceptions that are emotionally important to us (see Figure 2.2). The amygdala has rich connections with other cortical areas, which together give us the experience of emotion.

If David had no emotional response to seeing a face, how might this be tested? Emotion is processed not only in the brain but also in the autonomic nervous system (ANS), which prepares the body for dangerous situations. If we see a bear and run away, it is the sympathetic part of the ANS that makes us feel excited and moves blood to our muscles for a quick getaway. One easy way to measure the sympathetic nervous system is to pass a small electrical current along the skin, usually between the palm and the finger, to assess electrodermal activity (EDA). If we are excited, then our skin sweats slightly. This, in turn, makes it easier for the electrical current to pass between the two electrodes. Whenever we have an emotional response to what we see, we get changes in the EDA. David did not show any EDA differences when viewing pictures of those close to him. This suggested to Ramachandran that there was a disconnection between his visual face perception areas and the emotional centers of the brain. Since the auditory system is wired differently, that would also explain why David did not have the same experience when talking with his parents on the phone. The point of the story of David, as strange as it may seem, is to suggest that one important way to understand our mental processes is through their underlying mechanisms.

Figure 2.2 Amygdala and Other Areas of the Brain Associated With Emotion

We can discuss David on different levels. We can consider his actual behavior of saying his mother was not his mother. We can also ask David to tell us what he experiences when he sees his parents. In this case, David said that he sees them as nice people but that he does not expect from them what he expects from his parents. We can discuss how this affects other people, such as his parents, to be told they are not his parents. We can also look at the interaction between him and his parents. From another standpoint, we can consider cognitive and emotional mechanisms involved such as the memory of his mother and his emotional feeling for her. In other chapters of this book, I will include discussions of mental illness from the levels just described. In this present chapter, I will focus on current neuroscience approaches to understanding mental illness with an emphasis on brain imaging, genetics, and evolutionary perspectives.