Alcohol's Effects on Brain

by National Institute of Health

(Page 4 of 5)

Moderating Factors

Although heavy drinking during adolescence can impair brain functioning, not all young people who drink heavily or become alcohol dependent will experience the same level of impairment, and some may show no damage at all. This variability in the effects of heavy alcohol consumption is attributable at least in part to a large number of moderating factors, such as genetic influences (as represented by the adolescent's family history of AUDs), gender, age at onset of an AUD, drinking patterns and duration of abstinence, use of other drugs, and co-occurrence of other psychiatric disorders.

Family History of AUDs

AUDs, like other psychiatric disorders, tend to run in families, indicating that genetic factors play a role in the development of these disorders. In fact, much alcohol research focuses on identifying the gene or genes that predispose a person to developing an AUD. It is plausible that predisposing genetic factors as evidenced by a family history of AUDs also influence the effects of alcohol consumption on the adolescent brain. To explore this relationship further, Tapert and Brown investigated the moderating effects of family history of AUD on neuropsychological functioning in adolescents ages 13 to 18. Study participants were classified in four groups:

• Detoxified AOD-dependent adolescents with a family history of AUDs.
• Detoxified AOD-dependent adolescents without a family history of AUDs.
• Non-AOD-abusing adolescents with a family history of AUDs.
• Non-AOD-abusing adolescents without a family history of AUDs.

The investigators administered a battery of neuropsychological tests of language, visuospatial ability, verbal memory, attention, and executive functioning to all four groups. They found that both AOD dependence and family history were associated with level of language and attention functioning. Specifically, the investigators made the following observations:

Among adolescents who did not abuse AODs, those with a family history of AUDs had lower scores on language tasks than did those without such a family history, suggesting that genetic factors, or possibly family environment, may contribute to lower language skills in some adolescents.

Among adolescents without a family history of alcohol use disorders, those who were AOD dependent performed worse on attention tasks than did those who were not AOD dependent, suggesting that heavy AOD use may interfere with attention skills.

Performance levels on language and attention tasks were similar for AOD-dependent adolescents without a family history and for those who did not abuse AODs but had a family history of alcohol use disorders.

Hill and Shen also have assessed the influence of family history using ERP studies. These investigators found that children of alcoholics may be somewhat delayed in developing normal P300 patterns, yet appear to "catch up" to the levels seen in control subjects by young adulthood.

Taken together, these findings suggest that AOD dependence and family history of AUDs are distinct risk factors for decrements in neuropsychological performance, and these factors appear to impact different areas of neuropsychological functioning.

Gender Differences

Research with older adults has repeatedly suggested that women are more vulnerable to some effects of alcohol. For example, women appear to develop liver damage after lower overall alcohol consumption than men. Women also are more vulnerable to alcohol's toxic effects on the brain. However, only a few studies have analyzed gender differences among young adults with AUDs. One study compared male and female adolescents with AUDs to nonabusing male and female control subjects on various neuropsychological tasks. This study found that alcohol-abusing males outperformed male control subjects on a problem-solving task, whereas females with AUDs performed worse than the female control subjects. The investigators postulated that alcohol may affect frontal lobe functioning, which is required for these problem-solving tasks, more readily in females than in males.

Age at Onset of AUD

Because the brain continues to mature throughout adolescence, it is reasonable to speculate that the effects of heavy drinking on the brain may differ depending on the age at which an adolescent developed an AUD. A neuropsychological study investigating cognitive deficits as a function of age at onset and duration of an AUD found that participants with early-onset alcoholism showed the greatest degree of cognitive impairment.

Other researchers have examined the effects of age at onset of alcoholism using imaging techniques. Demir and colleagues used single photon emission computed tomography (SPECT) to measure blood flow through various brain regions. This regional cerebral blood flow (rCBF) is a measure of brain activity in those regions. Participants in this study were male alcoholics with early-onset (before age 20) and late-onset (after age 20) alcoholism as well as nonalcoholic control subjects. The investigators found that both early-onset and late-onset alcoholics showed impaired neuropsychological functioning and abnormal rCBF when compared with control subjects. Both groups of alcoholics had decreased rCBF in the left superior frontal regions compared with control participants. Late-onset alcoholics also showed decreased blood flow in the right superior frontal region. However, early-onset and late-onset alcoholics did not differ on most measures of rCBF and neuropsychological performance. In contrast to the study by Pishkin and colleagues, these findings suggest that earlier onset of heavy drinking is not necessarily more detrimental to brain functioning than late onset.

Drinking Patterns

Numerous studies have demonstrated that the effects of alcohol depend not only on the amount of alcohol consumed but also on the pattern of consumption. In general, drinking moderate alcohol amounts (one or two glasses of alcohol) almost every day appears to be less harmful than consuming the same total amount (that is, 7 to 14 glasses) on just one or two occasions per week - a pattern known as binge drinking or heavy episodic drinking. Heavy episodic drinking, which often is associated with hangover or mild withdrawal symptoms, is particularly common in adolescents and young adults, among whom this drinking pattern appears to be related to cognitive impairment. For example, in their 8-year followup study of adolescents with AUDs, Tapert and colleagues found that having more hangover or alcohol withdrawal symptoms (which indicates a pattern of heavy episodic drinking) predicted poorer visuospatial functioning in young adulthood. This relationship was observed even after controlling for visuospatial functioning at the beginning of the study, AOD use, and practice effects from the previous administration of the neuropsychological tests.

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