Key Role of Psychological Tasks and Brain States

Functional imaging shows the brain "at work.'' The type and amount of work are specified in a task per

Brain Scanning/Neuroimaging formed by the subject during the scanning procedure. Scans during two or more task conditions or states can be compared to show the brain areas that differ in activity between the conditions. Task condition is critical for functional imaging. During the early years of PET, many subjects were studied at rest with eyes closed and ears plugged; no task was used. These studies compared brain function during this "resting" state in one group of subjects to another group. The resting condition, however, is not particularly well controlled because subjects are free to engage in any cognitive activity to pass the time during the scan procedure. Moreover, even when a specific task condition is compared to a resting condition, the same problem remains. The choice of a control task, therefore, is often more complex than choosing a "resting" state. As cognitive psychologists and neuropsychologists have engaged in functional imaging experiments, the choice of tasks has become more sophisticated. Many tasks are chosen to maximize elemental cognitive processes and to minimize individual differences in performance and learning (habituation). These studies tend to focus on localizing brain areas involved in various aspects of cognition. Many a priori hypotheses from a cognitive neuropsychology perspective have been tested by comparing such tasks as generating words, listening to words, and speaking words. Other tasks are chosen to maximize performance differences among individuals to help identify relationships between brain activation and performance. These studies address questions concerning task difficulty, mental effort, and other parameters of performance. For example, one may use a test of reasoning to identify salient brain areas and then use easy and hard versions of the reasoning task to help identify relationships between mental effort and regional brain activation. The more complex the task, the more difficult it is to interpret the results in terms of elemental cognitive processes. Nonetheless, complex tasks can be used to examine performance differences and the functional relationships among brain areas. Because the manipulation of brain engagement and state are critical in functional imaging, these techniques are fundamentally psychological.

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