The hippocampus is a brain structure vital to learning and memory. It also appears vulnerable to damage from chronic, heavy alcohol consumption. An examination of alcohol's effects on the hippocampus has found that heavy drinking can reduce total hippocampus volume, which likely reflects a loss of hippocampal tissue substance.
Results are published in the November issue of Alcoholism: Clinical & Experimental Research.
"The hippocampus actually refers to two structures, the right hippocampus and the left hippocampus that are located in the right and left temporal lobes of the brain," explained Thomas P. Beresford, Department of Veterans Affairs physician, and professor of psychiatry at the University of Colorado Health Sciences Center. "Most scientists think that the hippocampus helps the brain manage learning, especially learning and remembering new things or things that happened recently. Before this study, researchers had noticed that the volume of the hippocampus seemed to be smaller in people who frequently drank large amounts of alcohol for long periods of time." Beresford is also the corresponding author for the study.
"The hippocampus is known to be injured by chronic stress and in Alzheimer's disease," added Gary Wand, professor of medicine and psychiatry, as well as director of the Endocrine Training Program at The Johns Hopkins University School of Medicine. "Although previous studies have shown a similar effect, this study was better controlled ... making the findings more believable."
Researchers used magnetic resonance imaging (MRI) scans to compare hippocampus volumes among adult male veterans who were both alcoholics (n=8) and non-alcoholics (n=8). All of the alcoholics had long, heavy drinking careers and were still drinking heavily at the time of the study. "Control" subjects were matched to the alcoholics by age and ethnicity.
"We made a special effort in this study to include only people who did not have any of the things that other scientists think might make the hippocampus smaller, such as post-traumatic stress disorder," said Beresford. "By excluding these people, we could focus only on the effects of chronic, heavy drinking."
Study results indicate a reduction in total hippocampus volume among the alcoholics.
"When we took a picture of the alcoholic brains using MRI, and measured the hippocampus," said Beresford, "it was much smaller than the hippocampus in the group of people who did not drink alcohol heavily. This means that alcohol appears to injure the hippocampus by itself. That is, it may harm the hippocampus in a way that other things do not."
"These findings may explain some of the memory impairment and cognitive deficits described in chronic alcoholics," added Wand. "It is unclear if the effect is reversible. It has been shown that stress-induced effects on hippocampal volume are reversible." Wand suggested future studies use a larger sample of subjects, and also noted -- given that alcoholism is partially an inherited disorder -- that persons predisposed toward alcoholism might already have a smaller hippocampus prior to the onset of heavy drinking compared to persons not predisposed.
Beresford agreed. "This study is only a first step," he said. "We are now studying what happens to the hippocampus in heavy drinkers when they stop drinking, whether the hippocampus heals itself or not, and what we might do to help healing along. Since the hippocampus is connected to many other parts of the brain, it is difficult to know all of the things that it does. Most scientists think that injury to the hippocampus makes it harder to learn things, especially to keep memories of new things or of new patterns. Understanding this, and how alcohol-dependent individuals may cope and even heal, is the point of our research."
Alcoholism: Clinical & Experimental Research (ACER) is the official journal of the Research Society on Alcoholism and the International Society for Biomedical Research on Alcoholism. Co-authors of the ACER paper, "Hippocampus Volume Loss Due to Chronic Heavy Drinking," were: David B. Arciniegas of the Departments of Psychiatry and Neurology at the University of Colorado School of Medicine; Julie Alfers, Lori Clapp and Brandon Martin of the Department of Psychiatry of the University of Colorado School of Medicine; Yiping Du of the Departments of Psychiatry and Radiology of the University of Colorado School of Medicine; and Dengfeng Liu, Dinggang Shen, and Christos Davatzikos of the Department of Radiology at the University of Pennsylvania. The study was funded by the National Institute on Alcohol Abuse and Alcoholism.
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