New research is beginning to explain how the brains of alcoholics become smaller and lighter compared to those of non-drinkers, and what functions may be lost due to chronic drinking. Scientists believe a number of factors - including alcohol's toxic byproducts, malnutrition, even cirrhosis of the liver - interact in complex ways to cause brain damage.
A compilation of studies on alcohol-related brain shrinkage presented by researchers at a symposium in Germany last fall is being published Wednesday in the journal Alcoholism: Clinical and Experimental Research.
The researchers used human and animal studies to map the damage.
Alcohol appears to be particularly damaging to the "white matter" or "hard wiring" _ fat-insulated nerve fibers that allow brain cells to rapidly communicate with other parts of the brain _ according to Dr. Clive Harper, a professor of neuropathology at the University of Sydney in Australia and organizer of the symposium.
Alcoholics can also have shrinkage or retraction of dendrites. These shorter connective fibers allow each nerve cell to "talk" with as many as 10,000 neighboring neurons at a time.
"The most important permanent structural change is nerve-cell loss," Harper said. "Some nerve cells cannot be replaced _ those in the frontal cortex, the cerebellum and several regions deep in the brain."
A separate study on mice, published in the same journal but not one of the symposium reports, showed that continuous drinking for as little as eight weeks can produce deficits in learning and memory that continue for up to 12 weeks after drinking stops.
"The learning and memory deficits we found in our mice ... affect all types of learning and memory," said Susan Farr, an associate professor of medicine at St. Louis University and an author of the study. "We found deficits in every type of task we tested the mice in."
Previous studies had suggested that mice had to drink steadily for six months or more to experience permanent deficits.
"Drinking doesn't just produce a hangover," said D. Allan Butterfield, a professor of biological and physical chemistry at the University of Kentucky. "Chronic drinking may lead to permanent cognitive deficits," he added, noting that the findings should be of particular concern to college students who engage in binge drinking.
Farr said it's difficult to make precise comparisons between the alcohol dosing of 8-week-old mice and humans.
"This would be equivalent to a human that drank six to eight beers or a bottle of wine every day for six years, and could experience learning and memory deficits for up to nine years after they stopped drinking," she said.
But Harper said many studies show that some brain functions improve with abstinence over time.
"Although working memory, postural stability and visual-spatial ability may continue to show impairment for weeks to months with sobriety, with prolonged sobriety, these brain functions can show improvement."
Harper also noted that, in animal experiments, dendrites that shrink with chronic alcohol use "have been shown to grow and spread again after periods of abstinence _ weeks to months _ and have been accompanied by improved brain function."
Although it is widely accepted that a predisposition to alcoholism has a genetic component, researchers are still trying to assess how much the physical damage from alcohol further affects the wiring of addiction.
For instance, one study based on autopsies found that genes controlling the manufacture of proteins that help produce nerve insulation _ myelin _ were suppressed in the brain tissue of alcoholics compared with such genes in non-alcoholics.
Poster Comment:
Something I already knew..