When we make decisions, we’re not always in charge. We can be too impulsive or too deliberate for our own good; one moment we hotheadedly let our emotions get the better of us, and the next we’re paralyzed by uncertainty. Then we’ll pull a brilliant decision out of thin air—and wonder how we did it. Though we may have no idea how decision making happens, neuroscientists peering into our brains are beginning to get the picture. What they’re finding may not be what you want to hear, but it’s worth your while to listen.
Spots on Brains
Eye-popping color images of brain scans in the popular press imply that scientists are pinpointing the precise location in the brain of feelings like fear, disgust, pleasure, and trust. But the researchers doing this work are highly circumspect about just what these colorful spots show. The two most common scanning methods, PET (positron emission tomography) and fMRI (functional magnetic resonance imaging), offer only approximations of what’s really going on in the brain. PET, the older and less popular of the two, measures blood flow in the brain; fMRI measures the amount of oxygen in the blood. Local blood flow and oxygenation indicate how active a part of the brain is but offer a crude snapshot at best. These scanners typically can’t see anything smaller than a peppercorn and can take only one picture every two seconds. But neural activity in the brain can occur in a fraction of the space and time that scanners can reveal. Thus, the splashy images we see are impressionistic, and the conclusions researchers draw about them are usually qualified—and often disputed. Like the images themselves, the details of brain function are just beginning to come into focus.