Present at the Future Read Free Page A

to show details of the brain’s soft tissue. (Now it’s called a computed tomography, or CT, scan.) With a burst of radiation, a CT scan takes a two-dimensional “slice” of the brain, and by putting two-dimensional X-rays together with the aid of a computer, researchers can obtain a three-dimensional image, as Benedek envisioned. Images of the brain from a number of X-rays are digitized, and then reconstructed so that researchers have a cross-sectional view of any part of the brain. CT scans can detect brain damage and can measure brain activity by monitoring blood flow as the patient performs a task. But just like Benedek’s early photos, CT scans have limits beyond revealing the brain’s structure.
    By the time X-rays were discovered, scientists were aware that living brains produce electrical activity. But not until the late 1920s did an Austrian psychiatrist, Hans Berger, actually record this activity for the first time. Berger made an electroencephalograph, another noninvasive way of studying the brain. Electrons fastened to a patient’s scalp pick up the electrical signals produced by the brain and send them to galvanometers, instruments that detect and measure small electrical currents. Like seismometers, which measure earthquakes, galvanometers used to be hooked up to pens that moved over a roll of graph paper to record the characteristic patterns of the current from the patient’s brain. Today, the patterns appear on a computer monitor, but electroencephalograms (EEGs) still allow scientists to monitor split-second brain activity and changes. EEGs can tell physicians whether you’re awake, asleep, or anesthetized—because your brain patterns look different in each of these states.
    During the 2005 debate over Terri Schiavo, the 41-year-old woman in Florida who had spent 15 years in a post-coma, or vegetative, state after a stroke, some physicians who had examined her reported that “her EEG is flat.” That meant that her brain was not producing any electricity at all. Since it was no longer functioning,its structure was deteriorating and filling with fluid so that it resembled the inside of a grapefruit. So EEGs can tell us a lot about the state of the brain, but they can’t tell us what regions of the brain do what.
    To look deeply into the brain, we now have positron emission tomography (PET) scans, which neuroscientists use frequently. To take a PET scan, a neurologist injects into a patient’s bloodstream a tiny amount of a radioactive substance, attached to glucose molecules that brain activity absorbs as fuel. In brain tissue, the glucose molecules give off gamma rays, recorded by sensors and then analyzed by computers to picture just where in the brain more glucose-molecule fuel is being used and where less is required. The result is a color-coded map of the brain, where red or yellow usually shows the more active areas that are using more fuel and blue indicates the less active areas that are consuming less fuel. The PET scan of a patient with Alzheimer’s disease, for example, is often mostly blue. Right now, PET scans can measure what is happening at 30-second intervals in a tiny portion of the brain. That, of course, is still not fast enough to keep up with brain activity.
    In 1977, there was a major breakthrough in brain imaging, the invention of functional magnetic resonance imaging, or fMRI. When you undergo magnetic resonance imaging (MRI), you lie on your back on a movable bed that slides into a giant circular magnet. MRI, like the other kinds of brain scans, isn’t at all painful—just uncomfortably noisy once the machine is turned on and begins generating a strong magnetic field. What happens is that the molecules in your body, including your brain, begin to behave like tiny magnets. The MRI machine’s magnetic field realigns the hydrogen atoms in your body so that instead of spinning in different directions, they all spin along the same axis, along the length of your body. Now the