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The MRI machine he designed is capable of imaging changes in blood-flow patterns in the human brain every 10 or 20 milliseconds, and can provide the images to researchers in real time. The resolution it can achieve is within a tenth of a second in time and a millimeter in space. It has allowed Cohen and his collaborators to set up what he calls "a psychology laboratory in a horizontal tube." While lying inside the scanner, research subjects and patients watch visual stimuli on a computer screen, listen to auditory stimuli and respond to what they're seeing by performing assigned tasks. While that's happening, Cohen and his collaborators take a series of MRI images of the subject's brain, in some cases monitoring brain electrical activity (EEG) as well. "With this technique," he explains, "it is possible for people to perform most any cognitive task, while we observe their brains using noninvasive, passive listening techniques and watch and record areas of brain activity." The MRI laboratory and scanner are used as a shared resource by many members of the UCLA research community, which means that the range of projects going on is enormous: from surgical planning—in which, for instance, a surgeon may determine in advance what part of the brain might either be safely removed or avoided carefully—to pure research projects. At present, Cohen and his collaborators are studying how the brain maps the positions of objects defined visually; how it maps and deals with color perception and the definition of objects; even how the brain is involved in the process of craving in nicotine addiction. Cohen's personal favorite area of study is the relationship between perception and sensation, a field of study known as mental imagery. From a range of experiments, Cohen and his colleagues have learned that the brain responds with a similar mechanism and similar computing machinery to both internally and externally generated perceptions. "The very same part of your brain that might perceive the motion of an external object," he explains, "is involved in thinking about moving things. But this concept has a flip side, which is that because of the way our brain perceives things, it is very tough for us to imagine things that aren't physical, and that we cannot hear, touch, taste or see. If you don't have sensory organs for it, your brain hasn't developed the neural machinery for it, and your mind can't access it. While exploring the physiological basis of pure imagination, we are also developing an understanding of the profound limitations on human consciousness." In fact, Cohen's list of projects his laboratory hopes to tackle seems to go on and on. Even he can't readily tick them all off: "The neuroanatomy of memory; what parts of the hippocampus are involved in what tasks; the laterality of brain functions, which is how cognitive tasks are split between left and right brain; the sensation of pain. Ahhhh, what else? The list is long and it's very, very hard to get to the end . . ." |
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