Alcohol : Effects on Physiologic Brain Functioning

by National Institute of Health

(Page 3 of 5)

The term "brain functioning" refers to measures of the brain's response to thinking and memory tasks. Researchers have attempted to determine whether and how heavy alcohol use by adolescents and young adults relates to abnormalities in brain functioning. These approaches have used such techniques as measuring event-related potentials (ERPs) and performing functional MRIs (fMRIs).

Nichols and Martin examined physiological brain functioning in young adult heavy drinkers by measuring ERPs - brain waves that occur in response to a sudden stimulus or unexpected event. In particular, the researchers studied a brain wave called P300, which typically occurs 300 milliseconds after a stimulus and serves as a measure of information processing. In this study, participants looking at a series of pictures depicting a common event (in this case, safe driving) interspersed with pictures of a rare or "oddball" event (e.g., an accident scene) had to respond when the oddball event occurred. Participants performed the task both under the influence of a sedative drug (benzodiazepine and after taking an inactive substance (i.e., placebo). The analyses revealed that under both conditions the P300 wave took longer to appear (i.e., had greater latency) in heavy-drinking young adults than in demographically comparable light drinkers. This result suggests that some information processing deficits exist that are related to heavy drinking and could represent an early stage along a continuum of alcohol-related brain damage.

The fMRI technique determines the activity in a brain region by detecting the amount of oxygen in the blood, which indicates the extent to which the brain region receives the oxygen it needs for nerve cell activity. If an fMRI is performed while the subject is engaged in a mental task, the level of activity in the brain regions involved can be identified. Tapert and colleagues used this approach to investigate brain response during a spatial working memory task in 15 adolescents with AUDs and 19 adolescents without AUDs (all ages 15 to 17). The participants were shown different abstract figures appearing one at a time in different locations on the screen, and were asked to press a button when a figure appeared in a repeat location. Youths with AUDs performed well on the task but showed greater blood oxygen levels in parietal regions and less response in some frontal and cerebellar areas compared with youths without AUDs. In a study of 10 alcohol-dependent young women ages 18 to 25 with longer histories of AUDs and 10 matched control women, however, the investigators found lower blood oxygen levels in many regions of the cerebral cortex in the alcohol-dependent women than in the control women. This decreased response, which signifies reduced brain activity, corresponded with poorer performance on the task, particularly as the task progressed. This research indicates that these key brain regions may not receive adequate oxygenated blood for sustained accurate performance on the task. This reduced activity may represent a subtle neuronal disruption in these regions.

Sensitivity to Alcohol

Numerous studies have described the effects of alcohol on the young brain, particularly with respect to sensitization. The term "sensitization" refers to the fact that with increasing alcohol exposure, people may experience an intensified positive response to alcohol - that is, the reinforcing effect of drinking becomes more powerful,3 and certain other behavioral responses (e.g., aggression or intake of more alcohol or other drugs) become amplified. ("Reinforcing effects" are the consequences of alcohol use, such as feelings of well-being or euphoria, that promote further alcohol consumption.) Some researchers have hypothesized that young people may be more likely to experience sensitization (and therefore may be more likely to consume excessive amounts of alcohol and develop AUDs) because their brains are still maturing, and the changes associated with this maturation could enhance the sensitization process.

For example, Chambers and colleagues proposed several reasons why young people might be particularly vulnerable to AOD use disorders. First, the brain continues to mature during adolescence, and disrupting the maturation process may damage brain function in the long term. Second, adolescents are more likely than people at other developmental stages to engage in impulsive behaviors, including heavy drinking. Impulse control is mediated by the prefrontal cortex, a region in the front of the brain.4 (4 The prefrontal cortex often appears to function abnormally in people with AOD use disorders.) Because the prefrontal cortex continues to develop during adolescence, teens have not yet gained their full ability to control impulsive behavior and are therefore more prone to poor judgment related to drinking. One of the effects of consuming alcohol is that the brain releases a signaling molecule (i.e., a neurotransmitter) called dopamine in a brain region known as the nucleus accumbens. Dopamine release activates the nucleus accumbens, which in turn stimulates the brain's reward system and triggers the desire for further positive stimulation, resulting in more alcohol use. Eventually, alcohol-related dopamine release may result in changes in brain development that lead to sensitization. This process also occurs in older people, but may be accelerated when it occurs in conjunction with the normal developmental changes in adolescents.

Summary of Alcohol's Effects

The preceding sections have shown that chronic heavy drinking during adolescence and into young adulthood appears associated with detrimental effects on brain development, brain functioning, and neuropsychological performance. Furthermore, imaging studies indicate that alcohol-consuming youth exhibit abnormalities in some brain areas that are particularly sensitive to disruption, such as the hippocampus, and in the chemical and electrical processes that occur during brain activity (e.g., in blood flow and the appearance of ERPs). These observations suggest that alcohol exposure during adolescence and young adulthood can cause subtle yet consequential damage. However, longitudinal studies that follow participants over several years will be needed to confirm this hypothesis.

About the Author

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.