An excessively shortened view of the future may explain substance abuse and
dependence, risk-taking behaviors, youth crimes, and a wide variety of
self-destructive behaviors, according to Warren Bickel, Ph.D., and other
like-minded researchers in a unique multidisciplinary area.
This research combines the theories, tools, and technologies used in
neuroscience, behavioral psychology, and economics to seek the common
processes behind these seemingly unrelated human phenomena.
Warren Bickel, Ph.D., a professor of psychiatry and chair of Alcohol
Abuse and Drug Prevention at the University of Arkansas for Medical Sciences,
uses tools in neuroimaging and economics to uncover the roots of
Credit: The Psychiatric Institute, UAMS
Bickel, a professor of psychiatry, the Wilbur D. Mills Chair of Alcohol
Abuse and Drug Prevention, and director of the Center for Addiction Research
at Psychiatric Research Institute at the University of Arkansas for Medical
Sciences, uses the term "tyranny of small decisions" to describe
how a person "can be victimized by the narrowness of the temporal
context" in his or her decision-making process. Various self-destructive
behaviors, he told Psychiatric News, are largely the result of a
person's inability to think far into the
This inability is directly related to addiction. A hallmark of dependence
and abuse is to seek an immediate high despite repeated, clear negative
consequences and a person's desire to quit.
"Why do addicts make poor decisions when they clearly face bad
consequences that would cost themselves severely?" Bickel attributed the
self-destructive tendency, at least in part, to these individuals' inability
to evaluate rationally the trade-off between instant gratification and future
Borrowed from behavioral economics, an important tool Bickel uses in his
addiction research is temporal discounting, which measures how a person weighs
the relative values of immediate and delayed rewards. The test subject is
asked to choose between two hypothetical rewards: either receiving $1,000 in a
month or a smaller amount now. If the current prize is also $1,000, an average
person would choose the prize now. As the current reward is reduced to $950,
$900, $850, and so on, while the future prize is held constant, a person will
eventually switch from the smaller current prize to the larger future prize.
The trade-off amount is a discount against the future constant. The larger the
discount due to delay would indicate a greater unwillingness to wait and can
be used to measure how impulsive a person is.
Temporal discounting ties addiction to abnormally high impulsivity and a
severely narrowed view of the future, Bickel said. The link has been
demonstrated in human as well as animal research, which shows that chronic
self-administration of certain substances such as amphetamine can alter the
extent of discounting. In a review published in the September 2007 Drug
and Alcohol Dependence (Supplement), Bickel and colleagues noted that
previous studies have found that people with opioid and cocaine dependence,
drinking and gambling problems, and a smoking habit discount the future
significantly more than nonaddicted controls. In a study they published in the
July 2008 Drug and Alcohol Dependence, cigarette smokers discounted
the hypothetical future, as well as past monetary gains significantly more
than nonsmoking controls.
To understand the physiology of behavioral patterns, scientists use
neuroeconomics to uncover the mechanisms underlying how people perceive the
cost of their choices and make trade-off decisions in the context of time. A
number of new studies have found evidence to support the connection between
addiction and impulsivity.
Two systems in the brain compete in the temporal discounting process: the
impulsive system that wants the reward immediately and the executive system
that evaluates rationally the temporal consequences and restrains the urge of
instant gratification, Bickel explained.
In a study published in the October 15, 2004, Science, Samuel
McClure and colleagues used functional magnetic resonance imaging scans to
demonstrate the two systems involved in the time-discounting decisions. Parts
of the limbic system associated with the midbrain dopamine system are
activated by immediate rewards. This is consistent with knowledge about
dopamine's role in addiction and the overall reward system. However, choosing
a delayed reward required greater activities in the lateral prefrontal cortex
and posterior parietal cortex, McClure found.
Bickel calls the theory of two systems the "competing neurobehavioral
decision systems hypothesis." Impulses are primarily driven by
activities in the limbic region, ventral striatum, and nucleus accumbens. The
executive system, in contrast, is known to be carried out in the prefrontal
cortex and dorsolateral prefrontal cortex, which are central to learning,
planning, regulating impulses, and making rational decisions. In other words,
the executive system regulates the urges for immediate reward and considers
whether a delayed reward is more valuable.
In individuals with addiction, this balance is tipped in the direction of
the impulsive system, and a person's reason and future outlook are severely
Are individuals with addiction born with a vulnerable executive
neurocircuitry that make them more susceptible to substance abuse? Or is
substance abuse responsible for damaged brain functions? There is evidence to
support both scenarios, and the interaction between innate predisposition and
the environment is a plausible explanation.
A recent study, published in the December 31, 2008, Journal of
Neuroscience, provides a glimpse of one biochemical pathway for
risk-taking behavior and addiction. David Zald, Ph.D., and colleagues at
Vanderbilt University found that these individuals have lower density of
dopamine autoreceptors in the brain than control individuals. These
autoreceptors normally "wipe up" the amount of free dopamine after
it is initially released. With fewer autoreceptors, these people are more
likely to have a greater "rush" after a dopamine-triggering
stimulus, leading to greater temptation for seeking the next reward.
In addition, neuroimaging research in recent years undertaken by Nora
Volkow, M.D., director of the National Institute on Drug Abuse, and other
scientists suggests that long-term abuse of substances is associated with
normal neurocircuits being compromised and the cognitive and executive
functions being damaged (Psychiatric News, July 6, 2007).
The chicken-and-egg question is less important than what can be done to
prevent or reverse the nature-environment feedback loop that pushes people
into a downward spiral, according to Bickel. He suggested that public policies
to promote a long-term view may help children and adolescents to extend their
temporal horizon and reduce the discounting of future reward.
Brain-imaging research has shown that adolescence is a period of incomplete
development of the executive function accompanied by peak activities in the
nucleus accumbens, the brain's center for reward and pleasure. It is no
coincidence that the majority of alcohol and substance use as well as smoking
begin in teenage years and peak during adolescence and young adulthood, Bickel
said. A similar time profile is seen in crime rates and impulsive, risk-taking
behaviors such as unsafe sexual practices. "Risk is a biologically
normal event among adolescents," said Bickel, because they have a"
shortened temporal view of life events and choices."
"It may be important to train executive and cognitive function in
children or strengthen their capacity in this area," Bickel said. Early
training for children and adolescents specifically to extend their long-term
outlook from a young age could make a big difference in preventing addiction
and other risky, self-destructive behaviors, he suggested.
Fortifying executive function and restraining impulsivity are possible with
active interventions. "The prefrontal cortex is very plastic,"
Bickel said. It is possible to escape "the tyranny of small
decisions" even for victims of addiction whose brain functions have
already been eroded, he believes, pointing to the effectiveness of contingency
management of addiction and replacement medications in tempering a hyperactive
impulsivity and in treating addiction. Future medications may boost a person's
hypoactive executive functions.
There is ongoing research into whether cognitive and executive functions
can be restored in those with brain damage from traumatic brain injuries or
schizophrenia. It remains to be seen whether neurological deficits related to
substance use can be similarly reversed. ▪