After a few beers, some people may forget where they put their keys, but hardened drinkers face a greater risk: permanent amnesia. Neuroscientists have suspected that alcohol kills neurons in a brain region associated with long-term memory. A study in the latest issue of Hippocampus, however, suggests that researchers may have to look elsewhere for the cause of lost memories.
Up to 5% of alcoholics in the United States develop Korsakoff's psychosis, a chronic disease that wipes out memories and can prevent new ones from forming. Experiments on rodents suggested that repeated high doses of alcohol destroy neurons in the hippocampus. The link became firmer after computerized tomography scans of alcoholic people revealed shrinkage in the hippocampus, a brain center that tags information for storage as memories.
Anthony Harding, a neuroscientist at the Prince of Wales Medical Research Institute in Randwick, Australia, wanted to see if a loss of neurons is behind the memory-center downsizing. He and colleagues at the University of Sydney took samples from the brains of 12 deceased alcoholics who had drunk the equivalent of more than a six-pack of beer every day for at least 20 years. They counted just as many hippocampal neurons in the alcoholics--even in five diagnosed with Korsakoff's psychosis--as in eight nonalcoholics' brains.
The finding suggests that neuroscientists "will have to look at other parts of the brain for the cause of memory loss," says Harding. The hippocampus does indeed shrink somewhat in alcoholics, Harding notes, but that's because the white matter--the insulating sheath of neurons--erodes. This process, he believes, would not lead to permanent memory loss, as white matter is restored after alcoholics quit drinking.
Harding also argues that because rodent studies suggest that these animals do lose neurons to alcohol, they may be unreliable models for the human hippocampus. But other experts are not ready to give up just yet. Sandra Kelly, a behavioral neuroscientist at the University of South Carolina, points out that neurons in rodent brains have been assayed with methods less accurate than those Harding used. A comparable study, she says, may find that lab rats also do not lose hippocampal cells--and thus redeem them as a research tool in studies on the link between alcoholism and memory loss.