Alcohol, Violence and Aggression
Scientists and nonscientists alike have long recognized a
two-way association between alcohol consumption and violent or
aggressive behavior. Not only may alcohol consumption promote
aggressiveness, but victimization may lead to excessive alcohol
consumption. Violence may be defined as behavior that
intentionally inflicts, or attempts to inflict, physical harm.
Violence falls within the broader category of aggression, which
also includes behaviors that are threatening, hostile, or
damaging in a nonphysical way. This Alcohol Alert explores the
association between alcohol consumption, violence, and
aggression and the role of the brain in regulating these
behaviors. Understanding the nature of these associations is
essential to breaking the cycle of alcohol misuse and violence.
Extent of the Alcohol-Violence Association
Based on published studies, Roizen summarized the percentages of
violent offenders who were drinking at the time of the offense
as follows: up to 86 percent of homicide offenders, 37 percent
of assault offenders, 60 percent of sexual offenders, up to 57
percent of men and 27 percent of women involved in marital
violence, and 13 percent of child abusers. These figures are the
upper limits of a wide range of estimates. In a community-based
study, Pernanen found that 42 percent of violent crimes reported
to the police involved alcohol, although 51 percent of the
victims interviewed believed that their assailants had been
drinking.
Alcohol-Violence Relationships
Several models have been proposed to explain the complex
relationships between violence or aggression and alcohol
consumption. To avoid exposing human or animal subjects to
potentially serious injury, research results discussed below are
largely based on experiments on nonphysical aggression. Other
studies involving humans are based on epidemiological surveys or
data obtained from archival or official sources.
Alcohol Misuse Preceding Violence
Direct Effects of Alcohol.
Alcohol may encourage aggression or violence by disrupting
normal brain function. According to the disinhibition
hypothesis, for example, alcohol weakens brain mechanisms that
normally restrain impulsive behaviors, including inappropriate
aggression. By impairing information processing, alcohol can
also lead a person to misjudge social cues, thereby overreacting
to a perceived threat. Simultaneously, a narrowing of attention
may lead to an inaccurate assessment of the future risks of
acting on an immediate violent impulse.
Many researchers have explored the relationship of alcohol to
aggression using variations of an experimental approach
developed more than 35 years ago. In a typical example, a
subject administers electric shocks or other painful stimuli to
an unseen "opponent," ostensibly as part of a competitive task
involving learning and reaction time. Unknown to the subject,
the reactions of the nonexistent opponent are simulated by a
computer. Subjects perform both while sober and after consuming
alcohol. In many studies, subjects exhibited increased
aggressiveness (e.g., by administering stronger shocks) in
proportion to increasing alcohol consumption.
These findings suggest that alcohol may facilitate aggressive
behavior. However, subjects rarely increased their aggression
unless they felt threatened or provoked. Moreover, neither
intoxicated nor sober participants administered painful stimuli
when nonaggressive means of communication (e.g., a signal lamp)
were also available.
These results are consistent with the real-world observation
that intoxication alone does not cause violence. The following
subsections explore some mechanisms whereby alcohol's direct
effects may interact with other factors to influence the
expression of aggression.
Social and Cultural Expectancies.
Alcohol consumption may promote aggression because people expect
it to. For example, research using real and mock alcoholic
beverages shows that people who believe they have consumed
alcohol begin to act more aggressively, regardless of which
beverage they actually consumed. Alcohol-related expectancies
that promote male aggressiveness, combined with the widespread
perception of intoxicated women as sexually receptive and less
able to defend themselves, could account for the association
between drinking and date rape.
In addition, a person who intends to engage in a violent act may
drink to bolster his or her courage or in hopes of evading
punishment or censure. The motive of drinking to avoid censure
is encouraged by the popular view of intoxication as a
"time-out," during which one is not subject to the same rules of
conduct as when sober.
Violence Preceding Alcohol Misuse
Childhood Victimization.
A history of childhood sexual abuse or neglect is more likely
among women with alcohol problems than among women without
alcohol problems. Widom and colleagues found no relationship
between childhood victimization and subsequent alcohol misuse in
men. Even children who only witness family violence may learn to
imitate the roles of aggressors or victims, setting the stage
for alcohol abuse and violence to persist over generations.
Finally, obstetric complications that damage the nervous system
at birth, combined with subsequent parental neglect such as
might occur in an alcoholic family, may predispose one to
violence, crime, and other behavioral problems by age 18.
Violent Lifestyles.
Violence may precede alcohol misuse in offenders as well as
victims. For example, violent people may be more likely than
nonviolent people to select or encounter social situations and
subcultures that encourage heavy drinking. In summary, violence
may contribute to alcohol consumption, which in turn may
perpetuate violence.
Common Causes for Alcohol Misuse and Violence
In many cases, abuse of alcohol and a propensity to violence may
stem from a common cause. This cause may be a temperamental
trait, such as a risk-seeking personality, or a social
environment (e.g., delinquent peers or lack of parental
supervision) that encourages or contributes to deviant behavior.
Another example of a common cause relates to the frequent
co-occurrence of antisocial personality disorder (ASPD) and
early-onset (i.e., type II) alcoholism. ASPD is a psychiatric
disorder characterized by a disregard for the rights of others,
often manifested as a violent or criminal lifestyle. Type II
alcoholism is characterized by high heritability from father to
son; early onset of alcoholism (often during adolescence); and
antisocial, sometimes violent, behavioral traits. Type II
alcoholics and persons with ASPD overlap in their tendency to
violence and excessive alcohol consumption and may share a
genetic basis.
Spurious Associations
Spurious associations between alcohol consumption and violence
may arise by chance or coincidence, with no direct or common
cause. For example, drinking is a common social activity for
many adult Americans, especially those most likely to commit
violent acts. Therefore, drinking and violence may occur
together by chance. In addition, violent criminals who drink
heavily are more likely than less intoxicated offenders to be
caught and consequently are overrepresented in samples of
convicts or arrestees. Spurious associations may sometimes be
difficult to distinguish from common-cause associations.
Physiology of Violence
Although individual behavior is shaped in part by the
environment, it is also influenced by biological factors (e.g.,
hormones) and ultimately planned and directed by the brain.
Individual differences in brain chemistry may explain the
observation that excessive alcohol consumption may consistently
promote aggression in some persons, but not in others. The
following subsections highlight some areas of intensive study.
Serotonin
Serotonin, a chemical messenger in the brain, is thought to
function as a behavioral inhibitor. Thus, decreased serotonin
activity is associated with increased impulsivity and
aggressiveness as well as with early-onset alcoholism among men.
Researchers have developed an animal model that simulates many
of the characteristics of alcoholism in humans. Rhesus macaque
monkeys sometimes consume alcohol in sufficient quantities to
become intoxicated. Macaques with low serotonin activity consume
alcohol at elevated rates; these monkeys also demonstrate
impaired impulse control, resulting in excessive and
inappropriate aggression. This behavior and brain chemistry
closely resemble that of type II alcoholics. Interestingly,
among both macaques and humans, parental neglect leads to
early-onset aggression and excessive alcohol consumption in the
offspring, again correlated with decreased serotonin activity.
Although data are inconclusive, the alcohol-violence link may be
mediated by chemical messengers in addition to serotonin, such
as dopamine and norepinephrine. There is also considerable
overlap among nerve cell pathways in the brain that regulate
aspects of aggression, sexual behavior, and alcohol consumption.
These observations suggest a biological basis for the frequent
co-occurrence of alcohol intoxication and sexual violence.
Testosterone
The steroid hormone testosterone is responsible for the
development of male primary and secondary sexual
characteristics. High testosterone concentrations in criminals
have been associated with violence, suspiciousness, and
hostility. In animal experiments, alcohol administration
increased aggressive behavior in socially dominant squirrel
monkeys, who already exhibited high levels of aggression and
testosterone. Alcohol did not, however, increase aggression in
subordinate monkeys, which exhibited low levels of aggression
and testosterone.
These findings may shed some light on the life cycle of violence
in humans. In humans, violence occurs largely among adolescent
and young adult males, who tend to have high levels of
testosterone compared with the general population. Young men who
exhibit antisocial behaviors often "burn out" with age, becoming
less aggressive when they reach their forties. By that age,
testosterone concentrations are decreasing, while serotonin
concentrations are increasing, both factors that tend to
restrain violent behavior.
Conclusion
No one model can account for all individuals or types of
violence. Alcohol apparently may increase the risk of violent
behavior only for certain individuals or subpopulations and only
under some situations and social/cultural influences.
Although much remains to be learned, research suggests that some
violent behavior may be amenable to treatment and some may be
preventable. One study found decreased levels of marital
violence in couples who completed behavioral marital therapy for
alcoholism and remained sober during followup. Results of
another study suggest that a 10-percent increase in the beer tax
could reduce murder by 0.3 percent, rape by 32 percent, and
robbery by 0.9 percent. Although these results are modest, they
indicate a direction for future research. In addition,
preliminary experiments have identified medications that have
the potential to reduce violent behavior. Such medications
include certain anticonvulsants (e.g., carbamazepine) ; mood
stabilizers (e.g., lithium) ; and antidepressants, especially
those that increase serotonin activity (e.g., fluoxetine)
However, these studies either did not differentiate alcoholic
from nonalcoholic subjects or excluded alcoholics from
participation.