Thursday, January 26, 2006

Your Brain on Booze

Scientists are using a new brain imaging technology to understand how chronic drinking damages wiring in the brain.

By Emily Singer

Knock back a few too many and you're likely to wake up with a hammering headache. But that short-term hangover pales in comparison to the long-term effects of alcoholism. Chronic drinking can lead to cognitive problems, such as impaired memory and problem-solving, and brain damage.

Scientists have already uncovered some of the major structural differences in the brains of alcoholics using magnetic resonance imaging, which gives a picture of the size and shape of different structures on the brain. But, until recently, researchers had been unable to study the fine network of nerve fibers that carry information from one brain area to another. These fibers are crucial for maintaining proper processing speed in the brain, so disrupting this circuitry could lead to many of the cognitive problems associated with alcoholism.

Now a new technology, known as Diffusion Tensor Imaging (DTI), is allowing researchers to examine how alcohol affects this fine-scale wiring. DTI measures the diffusion of water molecules in the brain. In many brain areas, water molecules move around randomly. But nerve fibers (commonly known as "white matter") are coated in a fatty substance, which forces water molecules to diffuse in the direction of the fiber. Scientists can construct a picture of the fiber tract by measuring the direction of diffusion. When water diffusion in a particular brain area is less organized than expected, scientists know there is a problem with the wiring in that area.

Edith Sullivan, a neuroscientist at Stanford, has spent the last 20 years studying how alcohol damages the brain. In the last few years, she's added DTI to her arsenal of brain-imaging techniques. Using it, she found that alcoholics have suffered damage to specific parts of their corpus callosum, the thick tract of white-matter fibers connecting the two hemispheres of the brain. Sullivan and colleagues also found that these abnormalities are linked to problems in attention and working memory, a form of memory allows one to remember, say, a phone number long enough to dial it.

Fortunately, research from Sullivan and others has shown that some parts of the brain can bounce back with sobriety. Now, Sullivan and collaborator Adolf Pfefferbaum, also at Stanford, are running a study of 200 healthy people, recovering alcoholics, and recovering alcoholics with HIV, to determine if the white-matter fibers can also recover.

"The brain damage [associated with alcoholism] is accrued over years and it will probably take years for the brain to recover," says Sullivan. "That means people have to be in some form of rehab for an extended period of time in order to recover and live a relatively normal life and perform at a pre-alcoholic level."

Daniel Hommer, chief of the brain imaging lab at the National Institute on Alcohol Abuse and Alcoholism in Bethesda, MD, says it's not yet clear how big a role changes in white matter play in alcoholism, but that DTI will allow scientists to answer that question.