Alcoholism Has Opposite Effects on Men's and Women's Brains
Certain types of brain tissue integrity may be reduced in alcoholic men and increased in alcoholic women.
Alcohol’s potential to harm the brain has been known for years, and accumulating evidence points to differences between men and women in the damage alcohol inflicts. For example, brain white matter volumes have been shown to be different in male and female alcoholics.
Now, a new study further illuminates the sex differences in alcoholics using diffusion tensor imaging, a type of magnetic resonance imaging that measures how water molecules move through brain tissue. The water serves as a proxy for electrical signals between neurons, and the imaging reveals fractional anisotropy, which is a measure of the tissue’s integrity.
To illustrate, imagine a water balloon, said Kayle Sawyer, a behavioral neurologist at the Boston University School of Medicine and first author of the study. Because the interior of the balloon is homogeneous and spherical, water molecules can travel unhindered in any direction. In a similarly spherical apple, water molecules can still travel in any direction, but they won’t move as far because they will run into cell walls, seeds and the like. These two objects are examples of isotropic media. In contrast, water molecules in a stick of celery have an easy time traveling along the long fibers and a hard time going crosswise to them.
A human neuron consists of a rounded cell with long fibrous extensions called axons. The round cell bodies constitute the gray matter at the surface of the brain and the axons are the white matter in the interior. Electrical signals move between neurons along the axons, which function like the long fibers in celery. The more extreme the difference between ease of travel in one direction versus its perpendicular, the more anisotropic the relationship is -- and the higher the anisotropy, the better the signal transmission.
Most alcoholism research has focused on men. In the United States there are about twice as many male alcoholics as females, but female alcoholics’ death rates are 50 to 100 percent higher than those of males, according to the National Institute on Alcoholism and Alcohol Abuse.
To investigate sex differences in how alcohol affects the brain, Sawyer and colleagues recruited 90 volunteers divided into four roughly equal groups: male and female alcoholics, and male and female nonalcoholics. The alcoholics had to be abstinent for at least four weeks in order to avoid confounding acute effects with long-term chronic effects on the brain. In addition to the fractional anisotropy scans, the researchers administered a comprehensive battery of psychological evaluations and ascertained participants’ drinking history, length of sobriety and familial alcohol use.
The researchers obtained images from three bundles of axons that connect the right and left hemispheres as well as other parts of the brain. These bundles coordinate everything from language and memory to jumping ability, and are particularly important for normal emotional function. This includes networks involved in reward and punishment -- known to be intimately involved in addiction -- which a previous study had shown were smaller in alcoholic men and larger in women compared to nonalcoholics of the respective sexes.
The new results, Sawyer said, confirmed that the alcoholic men had poorer white matter integrity than the nonalcoholic men, but “we didn’t find that for the [alcoholic] women.” In fact, the women alcoholics had slightly higher fractional anisotropy than any of the other groups, and longer sobriety correlated with higher fractional anisotropy for the men, but not the women. The study was published this past May in the journal Neuropsychopharmacology.
Sawyer cautioned that the results of this study don’t show whether the differences between male and female alcoholics are risk factors for, or consequences of, alcoholism.
“We didn’t scan these people before they started drinking,” Sawyer said. “The abnormalities might be part of the reason they started drinking,” rather than damage caused by drinking.
Nevertheless, the study revealed potentially important differences between the white matter of male and female alcoholics, according to John Matochik, a program officer at the National Institute on Alcoholism and Alcohol Abuse who was not involved in the project. He noted that the three regions with sex differences contribute to behavioral functions, and alcoholism could potentially change those behavioral functions in different ways for men and women.
"Understanding what functions are negatively affected by alcohol and which functions are spared could lead to tailored interventions for alcohol use disorders that consider the important role that sex differences may play," said Matochik.