excerpt from book:
Brain scan images are not what they seem…or at least not how the media often depict them. Nor are brain-scan images what they seem. They are not photographs of the brain in action in real time. Scientists can’t just look “in” the brain and see what it does. Those beautiful color-dappled images are actually representations of particular areas in the brain that are working the hardest— as measured by increased oxygen consumption— when a subject performs a task such as reading a passage or reacting to a stimuli, such as pictures of faces. The powerful computer located within the scanning machine transforms changes in oxygen levels into the familiar candy-colored splotches indicating the brain regions that become especially active during the subject’s performance. Despite well-informed inferences, the greatest challenge of imaging is that it is very difficult for scientists to look at a fiery spot on a brain scan and conclude with certainty what is going on in the mind of a person.