Story of Psychology - Morton Hunt [343]
In 1983 another important tool was introduced—CT (computed tomography) scanning, also known as CAT scanning (computerized axial tomography). It proved to be a valuable medical tool for assessing many kinds of physiological problems, but also for studying brain structure and identifying brain lesions. In the CT scan, the subject is, as in a PET scan, supine, and eased into the scanner, which has an X-ray source and a set of radiation detectors. The scanner sends radiation through the target part of the subject from various angles. The density of biological materials varies; accordingly, the data gathered by the detectors reveal the hidden structure, and are assembled by a computer program to yield X-ray pictures of the entire scanned target. CT scans were and are used primarily for clinical medical analyses, but the method also had some value for cognitive research on brain structure, although the results are not very distinct and lack fine resolution.25
By far the most important and latest new tool is the MRI (magnetic resonance imaging) scan. Again the subject is supine inside a scanning machine, which is about the size of a small SUV, and which, while making a horrendous racket, generates a powerful magnetic field that permeates the subject’s head. The magnetism, unlike the radiation of the CT scan, is harmless—and capable of revealing brain structure and activity far better than the CT scan.
It can do so because the protons of hydrogen, a major component of the water and fat in the brain, behave like tiny magnets and line up under the influence of the magnetic field (normally, their orientation, unaffected by earth’s weak magnetism, is randomly distributed). Then, radio waves, passed through the subject’s head, change the protons’ orientation, but the instant the radio waves stop, the protons bounce back to the orientation created by the magnetic field and, in so doing, emit energy signals. These, picked up by detectors, yield scans much clearer, and with far finer resolution (a spatial resolution of one millimeter and a temporal resolution of about one second) than any other scanning method.
Best of all, from the cognitive researcher’s viewpoint, if the subject performs some prescribed mental task while being scanned, the resulting fMRI (functional MRI) scan gives an intimate look at exactly which brain areas and substructures are active, and how active, during that kind of mental activity. Accordingly, the fMRI quickly became the workhorse of cognitive neuroscience. A dozen years ago, a mere handful of studies based on fMRI scans appeared in a year’s worth of research literature; today, the annual output is several thousand.26
What has all this done to psychology, the science of the human mind? That depends on who is assessing the situation.
Most psychologists, focused on mental processes rather than wetware, continue to use research methods that were available before the advent of scanning, but many of them also rely on the help of scanning. They no longer see cognitive psychology and cognitive neuroscience as distinct and unrelated fields. As Robert J. Sternberg, a notable cognitive psychologist, says, “Biology and behavior work together. They are not in any way mutually exclusive.”27 Some use stronger terms to appraise the impact of cognitive neuroscience: Psychologists Stephen Kosslyn and Robin Rosenberg write, “It is fair to say that neuroimaging techniques have transformed psychology, allowing researchers to answer questions that were hopelessly out of reach before the mid-1980s.”28
Does that suggest that cognitive neuroscience will become the psychology of the future? Not according to cognitivist Michael Posner, who has worked in both camps and whose work has been admired by researchers in both: “An impressive aspect of the anatomical methods such as PET and fMRI is how much they have supported the view that cognitive measures can be used to suggest separate neural structures,” and he stresses the importance of the contributions of both fields to understanding brain function.29