Alcohol : Effects on Brain Structure

by National Institute of Health

(Page 2 of 5)

In addition to neuropsychological analyses, scientists have conducted imaging studies in teens and young adults with AUDs to determine the effects of heavy drinking on the changing brain structure during this developmental stage. These studies have revealed a variety of structural brain abnormalities associated with alcohol use.

In one study, De Bellis and colleagues used an imaging technique called magnetic resonance imaging (MRI) to investigate the sizes (i.e., volumes) of various brain structures in adolescents and young adults with and without AUDs. These researchers measured the following:

Intracranial volume: Volume enclosed by the skull.

Cerebral volume: Volume of the largest and uppermost section of the brain, the cerebrum, which is divided into two halves or hemispheres.

Cortical gray-matter volume: Volume of the gray mass that consists primarily of nerve cell bodies and forms the outer layer of the cerebral hemispheres.

White-matter volume: Volume of the white mass that makes up most of the cerebrum and consists primarily of nerve cell extensions (axons) through which nerve cells connect with each other.

Corpus callosum volume: Volume of the bundle of nerve cell extensions that connect the cerebral hemispheres.

Amygdaloid volume: Volume of the amygdala, an almond-shaped gray-matter mass located deep in each cerebral hemisphere, which may play an important role in the development of repeated AOD use and AOD dependence.

Hippocampal volume: Volume of the hippocampus, a curved brain structure located in each cerebral hemisphere, which is critical to learning new information and forming memories.

When the investigators compared the volumes of these brain structures in adolescents and young adults with and without AUDs, only the hippocampal volumes differed significantly between the two groups. That is, left and right hippocampal volumes were significantly smaller in youths with AUDs than in matched control participants without AUDs. The researchers also found that hippocampal volume correlated positively with the age of onset of the AUD: The earlier a person developed an AUD, the smaller his or her hippocampi. Finally, a negative correlation was found between hippocampal volume and the duration of the AUD: Smaller hippocampi were found in participants who had longer-lasting AUDs than in subjects with AUDs of shorter duration. In another study of adolescents with and without AUDs who had no coexisting other drug use and other psychiatric disorders, Nagel and colleagues also detected smaller left hippocampal volumes in the adolescents with AUDs. These findings suggest that more enduring heavy-drinking patterns in adolescents and young adults are linked to smaller hippocampi and, because these brain structures are critical to learning and memory formation, may lead to more severe impairment of memory function.

Other studies that have looked at the effect of alcohol on the structure of white matter have identified subtle differences between youths with and without AUDs. In one preliminary study, Tapert and colleagues used a type of MRI technique, diffusion tensor imaging, to study the integrity of the white matter in the corpus callosum. This study determined that in youths with AUDs, white-matter integrity was reduced in the portion of the corpus callosum that is located toward the back of the brain. Moreover, in these young people, white-matter integrity tended to be reduced in the rest of the corpus callosum as well, although the reductions were not statistically significant. The study also found that decreased white-matter integrity was significantly related to longer duration of heavy alcohol use, greater number of past alcohol withdrawal symptoms, and recent consumption of large amounts of alcohol.

Taken together, these imaging studies indicate that youths with AUDs may have some subtle abnormalities in hippocampal volume and white-matter integrity compared with demographically similar young people without AUDs. Even these subtle alterations could lead to disturbances in brain function that may have a long-lasting influence on subsequent performance of thinking and memory tasks. Similar impairment of hippocampal function and memory function resulting from alcohol exposure during adolescence has been demonstrated in animal models, further supporting the critical role of alcohol's detrimental effects on this brain structure.

Although it is clear that heavy alcohol use can lead to changes in brain structure which can affect brain functioning, the reverse process - that an abnormality existing prior to alcohol exposure may predispose a person to alcohol use and the development of an AUD - also is plausible. In fact, both processes could occur in the same person, with a preexisting brain abnormality promoting heavy alcohol use, which then could lead to additional alterations in brain structure. To date, it is not known whether either of these processes takes precedence over the other or to what extent the processes co-occur in one person. This issue could be critically important to understanding the development of alcohol dependence in adolescents and young adults and to devising methods to prevent dependence, and therefore should be examined in future research that follows high-risk youths over time.

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NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.