Читать книгу Abnormal Psychology - William J. Ray - Страница 85

Functional magnetic resonance imaging (fMRI) is based on the fact that blood flow increases in active areas of the cortex. Specifically, hemoglobin, which carries oxygen in the bloodstream, has different magnetic properties before and after oxygen is absorbed. Thus, by measuring the ratio of hemoglobin with and without oxygen, the fMRI is able to map changes in cortical blood and infer neuronal activity.

Measurements using fMRI are made by having a person lie on his back inside a large magnet and radio frequency device, which measures changes in blood oxygen levels. Initially, a structural image of the brain is created (see Figure 2.15). In contrast, a structural image (MRI), like an X-ray, shows the anatomy of the brain but does not reflect activity. However, a reduction in brain volume is seen in a variety of disorders including schizophrenia. These measures can be determined from the MRI.

Blood flow measurements in the brain using fMRI are made by having a person lie on his back inside a large magnet and radio frequency device.

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Brain activity can be determined with the fMRI, or functional MRI. A common procedure for showing brain activity is to take a baseline in which the patient just relaxes. Following this baseline period, the patient performs specific tasks. The fMRI response recorded during the task is subtracted from that during the baseline period. This shows which specific areas of the brain are involved in performing a task. This information is then placed on the structural MRI image of the brain as shown in Figure 2.16. The color used reflects the amount of activity seen in a particular brain area. As you will see throughout this book, fMRI has been used with almost every disorder discussed. You can also compare one group of individuals with another. For example, Figure 2.17 shows that women with post-traumatic stress disorder (PTSD) activate different areas of the brain (the amygdala and insula) when processing emotional information compared with women without PTSD (Bruce et al., 2013).

Figure 2.15 Magnetic Resonance Imaging (MRI) Shows the Anatomy of the Brain

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