Читать книгу Abnormal Psychology - William J. Ray - Страница 84

Positron Emission Tomography (PET) is a measure related to blood flow in the brain that reflects cognitive processing. PET systems measure variations in cerebral blood flow that are correlated with brain activity. It is through blood flow that the brain obtains the oxygen and glucose from which it gets its energy. By measuring changes in blood flow in different brain areas, it is possible to infer which areas of the brain are more or less active during particular tasks. Blood flow using PET is measured after participants inhale, or are injected with, a tracer (a radioactive isotope) that travels in the bloodstream and is recorded by the PET scanner (a gamma ray detector). Figure 2.14 depicts a PET scan in which individuals with schizophrenia show less metabolism in the frontal lobes as compared with healthy controls (Buchsbaum & Haier, 1987).

Magnetoencephalography measures brain activity by measuring small magnetic fields produced in the brain.

National Institutes of Mental Health

The general procedure is to make a measurement during a control task that is subtracted from the reading taken during an experimental task. Although it takes some time to make a PET reading, which reduces its value in terms of temporal resolution, it is possible to determine specific areas of the brain that are active during different types of processing. Since PET can measure almost any molecule that can be radioactively labeled, it can be used to answer specific questions about perfusion, metabolism, and neurotransmitter turnover.

Figure 2.14 Comparing Positron Emission Tomography Scans

Source: Buchsbaum, M. S., & Haier, R. J. (1987), Functional and Anatomical Brain Imaging: Impact on Schizophrenia Research, Schizophrenia Bulletin, 13(1), 115–132.

Some of PET’s main disadvantages include expense; the need for a cyclotron to create radioactive agents; the injection of radioactive tracers, which limit the number of experimental sessions that can be run for a given individual; and limited temporal resolution. Due to risks associated with exposure to the radioactive tracer elements in a PET study, participants typically do not participate in more than one study per year, which limits the degree to which short-term treatment efficacy can be studied. With the development of fMRI, PET is no longer the technique of choice for research studies in psychopathology.

However, PET does offer an advantage for studying specific receptors such as dopamine receptors in the brain, which are particularly active in those with an addiction or inactive in those with Parkinson’s disease. Another study used PET to examine serotonin in those with social anxiety disorder (A. Frick et al., 2015). An overactive serotonin system was found at the synaptic level in those with social anxiety disorder as compared to matched controls.

functional magnetic resonance imaging (fMRI): a brain imaging technique that measures increased blood flow in active areas of the cortex by determining the ratio of hemoglobin with and without oxygen

diffusion tensor imaging (DTI): procedure that uses the magnetic resonance imaging (MRI) magnet to measure fiber tracts (white matter) in the brain