A Preview of Tomorrow's Medical Headlines

April 02, 1993

Four Johns Hopkins Medical Institutions experts addressed the American Society of Newspaper Editors Wednesday on medical stories that will be in the news in the next decade. Following are excerpts from their remarks.

Decade of the Brain

Solomon Snyder, professor and director of neuroscience:

President Bush declared the 1990s the Decade of the Brain. God willing, this will not be revoked by the Clinton administration, for I think it was a very wise idea. Brain research has catapulted forward at an extraordinarily accelerating rate. I will tell you about a few of the most exciting recent developments.

Your brain has about 10 billion separate nerve cells, or neurons. How they talk to each other is the basis of all the information processing in the brain. As you can imagine, there is a virtually infinite number of possible connections.

The way these 10 billion neurons talk to each other is by releasing chemical messengers which we call neurotransmitters. These act at specific recognition sites on receptors on adjacent neurons and then change normal functions. So one of the important efforts in biomedical research has been to try and understand what are those neurotransmitters, how are they made, how they are released, how do they act at the very specific recognition sites like a lock-in-key recognition.

One of the fundamental mysteries has to do with the neurotransmitters themselves. Neurons either fire or don't fire. Some neurotransmitters excite other neurons to make them fire, and other neurotransmitters inhibit other neurons to stop them from firing. In principle the brain could make do with one excitory and one inhibitory neurotransmitter, but it doesn't do that. There are 50 to 100 different neurotransmitters and they come in different chemical classes.

Understanding what the different ones do is key, not only in understanding the brain at the molecular level, but because they point to important therapeutic agents for medical conditions such as stroke.

The Machine at Work

Guy McKhann, professor of neurology and director of the Krieger Mind-Brain Institute:

I'd like to pick up on the theme that Dr. Snyder started and take this discussion in a little different direction.

If we want to get into the properties that we consider give us our humanness, we have to ask questions about such things as language function, memory, creativity, adaptability and how do we get to those questions in the human brain.

The biggest change over the last five or ten years is in our ability to image the human brain. Many people have had experiences with things like MRI scans. What we're talking about there is essentially the geography of the brain. Seeing the brain as a static organ is like looking at a machine which is turned off. It's telling you nothing about how it is working.

In the last few years there's been a new aspect of imaging which we call the functional imaging of the nervous system in which or by which one tries to ask the question what part of your brain do you use as you process information. The leading aspect of this is what we have called PET scanning, Positron Emission Tomography, based on the idea that if a group of neurons are being used, the regional blood flow changes and you can image off that blood flow.

So if I wonder what part of my brain do I use as I move my fingers, I can ask that question. If I ask a pianist to pretend he's playing something, what part of the brain does he use, we're able to ask that question. The implications of this for studying the normal, the normal variation and the injured brain are enormous.

. . . The brain is a very, very slow computer. The processing of information in the brain takes a half a second or three quarters of a second. Computers work in milliseconds. But the brain is infinitely adaptable. The brain is not a hard-wired organ. It's not something that was all wired up in your mother's womb and that's what you're stuck with. Your brain is constantly changing. Your brain now is different than your brain then and that's different than my brain.

Now what changes this? Well one of the things that changes your brain is use. Nor is this limited to development. There's increasing evidence that this occurs in a life-long pattern. By constantly challenging your brain, are you maintaining your intellectual capabilities in ways that you might not otherwise do? The answer seems obvious but how exactly one does that remains to be seen.

A last point about adaptability is the issue of response to injury. I as a neurologist may see two patients. Both have had a stroke, both have difficulty in using the left hand. One, over the next two to three weeks, gets better and a month later or two months later, I'm hard-pressed to find out that anything is wrong. The other, a year later, still has a significant deficit.

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