Medicine. - People who enjoy seeing the brain at work are probably not very sensitive to noise. Magnetic resonance imaging (or MRI) scanners, are noisy, and they can be expensive machines. But they do make it possible for doctors and researchers to see into the human brain. What they show in an Alzheimer's patient is a picture of destruction - especially if the illness has significantly progressed. If the memory loss has only recently begun, an MRI shows only diffuse or subtle changes. Then other tests are needed to confirm the diagnosis Alzheimer's disease.

Interviewer: Kristin Raabe

Nevertheless, MRI scans can be very helpful for Alzheimer's patients. That's what Paul Thompson of the University of California thinks:

In Alzheimer's disease, nerve cells in the brain are progressively destroyed. With the help of MRI brain scans, the actual brain cells themselves are not seen, but a doctor can see if there is any damage to the outer surface of the brain, the gray matter of the cortex. We know that this brain tissue is severely damaged in Alzheimer's disease: up to 10 per cent of these brain cells can be lost every year. And these cell losses in the illness can be quite easily identified.

But in an MRI picture, a doctor cannot easily see the extent of cell loss with the naked eye. Paul Thompson sought help from experts in Australia, and they managed to improve the resolution of the MRI pictures.

There are essentially two important aspects with this technology. First of all, a doctor makes very detailed images of the structure of the brain with an MRI scanner, and images are acquired at different time intervals. Ideally, the resolution should be better than a millimeter. Then the structural details of brain can be seen. Next, you need very powerful computers that can identify very subtle differences between the individual brain scans. Here's an example: If you compare a pair of brain images acquired only a few months apart, maybe at most five percent of the brain tissue is lost. The computer can calculate this figure precisely, for each brain region, visualizing how much brain tissue was destroyed in the course of a year. Then we can identify features that a doctor may not be able to identify with the naked eye.

Paul Thompson's team put several patients with Alzheimer's disease into the MRI scanner. These imaging studies were repeated several times over the course of a few months. Once all the images had been collected, a video sequence could be put together:

It was extremely interesting to see how Alzheimer's disease spreads in the brain. We were very surprised to see that this progression follows a similar pattern in each patient we studied. The destruction of brain tissue typically begins in the memory regions of the brain, and after about a year it moves forwards into the frontal territories of the brain. Those are the regions responsible for inhibition and behavioral control. Later on, even the emotional regions of the brain are engulfed. This sequence corresponds quite closely to the emergence of the symptoms that patients gradually develop.

But Paul Thompson's videos show not only how Alzheimer's gradually destroys the brain, but they also show the tissue that it leaves intact.

The greatest paradox, in this illness, is that during all this destruction some brain regions remain completely intact: regions involved in visual perception and sensation, for example. It is as if you were seeing a lava flow, spreading in the brain, but suddenly this lava completely jumps over some rocks, or flows around them, and those regions remain completely unaffected. We are very eager to know why that is. But right now, it's a mystery.