Problem 5. Addiction is a choice
Learning goals
Is addiction a choice? Why do we continue to take drugs even when we experience negative
consequences?
Can giving money help to quit an addiction?
What does behavioural economics say about decision making?
Bickel, W. K., Jarmolowicz, D. P., Mueller, E. T., & Gatchalian, K. M. (2011). The behavioral
economics and neuroeconomics of reinforcer pathologies: implications for etiology and
treatment of addiction. Current Psychiatry Reports, 406-415
Abstract
We describe addiction as pathological patterns of responding resulting from the persistently
high valuation of a reinforcer and/or an excessive preference for the immediate
consumption of that reinforcer. It is further suggested that, as indicated by the competing
neurobehavioral decision systems theory, these patterns of pathological choice and
consumption result from an imbalance between two distinct neurobehavioral systems.
Specifically, pathological patterns of responding result from hyperactivity in the
evolutionarily older impulsive system (which values immediate and low-cost rein- forcers)
and/or hypoactivity in the more recently evolved executive system (which is involved in the
valuation of delayed reinforcers). This approach is then used to explain five phenomena that
we believe any adequate theory of addiction must address.
Introduction
The strong interplay of data and theory would be useful in the study of addiction.
Behavioural economics has shown that addicts demonstrate extreme valuation of their
addictive reinforcer and preference for receiving it in the short term. We refer to these
patterns of reinforcer consumption as reinforcer pathology. Neuroeconomics has provided a
new conceptual model of addictive behavior that explains reinforcer pathology and provides
novel insights into the etiology and treatment of addiction.
Two general characteristics of reinforcer pathology
Reinforcer pathology (like overeating or drugtaking) refers to the presence of two distinct
but likely interacting repertoires that tend to be at the extremes of the distribution of
behaviors. More specifically, reinforcer pathologies result from 1) the persistently high
valuation of a reinforcer and/or 2) the excessive preference for the immediate acquisition or
consumption of a commodity despite long-term negative outcomes.
Research on the first feature uses the sophisticated quantitative concepts and procedures of
1) own-price elasticity of demand, and 2) cross-price elasticity of demand. Own-price
elasticity of demand refers to the sensitivity of a person’s consumption of a commodity
(reinforcer) to the price of the commodity. If sensitivity to price is very limited, then this
could reflect a pathological valuation of the commodity. Cross-price elasticity of demand
refers to the impact of changes in the price of one commodity on the consumption of
another fixed-price commodity. These interactions can result in substitution, in which the
,increases in price of one commodity increase the consumption of the other commodity, or
can result in a complementary interaction in which the increase in the price of one
commodity decreases the consumption of another commodity. In addictions, some
treatments are based on substitution, or some patterns of pathological consumption can be
related to complementary interactions.
The second feature is studied in research on delay discounting, which refers to the
observation that the value of rewards decreases as a function of delay until the time of their
receipt.
Demand and reinforcer pathology
Studies of reinforcer consumption as a function of price have revealed relationships between
elasticity of demand and consumption of pathological reinforcers. Excessively high valuation
of a given reinforcer and severity of reinforcer pathology are both defined by lack of
reduction of consumption of the reinforcer with increases in the price of the reinforcer.
Individuals suffering from reinforcer pathologies typically show this insensitivity of
consumption to price changes (i.e., demand inelasticity) for the substances that they abuse,
but not for nonpathological reinforcers.
Discounting and reinforcer pathology
The rate of delay discounting predicts several important behavioral patterns regarding
pathological reinforcers.
Research using delay discounting assessment procedures has determined that individuals
who suffer from reinforcement pathologies discount delayed rewards more than matched
controls. Opioid-dependent individuals discount hypothetical money more than community,
nondependent, matched controls. This result has been found for opioid-dependent
individuals; obese women; pathological gamblers; and individuals addicted to cocaine,
alcohol, and cigarettes. Furthermore, evidence suggests that severity of reinforcer pathology
is positively related to rates of discounting.
Although individuals’ rates of discounting for various commodities appear to be correlated,
evidence also suggests that those affected by reinforcement pathologies discount their
pathological reinforcer to a greater extent than they discount other commodities.
Interactions between demand and discounting approaches
The elasticity of demand (sensitivity of consumption to price) is determined in part by the
availability of substitutes. Such substitution would result in greater elasticity of demand for
the first commodity. One source of substitution is intertemporal (e.g., the individual might
not choose to purchase a commodity today at a higher price if he knows he can get it next
week at a lower price). Now, if the consumer of a commodity excessively discounts the
future, then this would functionally decrease the availability of intertemporal substitutes,
which in turn should result in less price sensitivity. This synergistic interaction between these
two processes may drive the price insensitivity to a point that characterizes reinforcer
pathology. This interplay between immediate reinforcers and their potential substitutes
merits exploration via the use of measures of demand and discounting in the same study.
Mackillop et al found that the measures of demand intensity and delay discounting were
correlated.
, The competing neurobehavioral decision system theory
Neuroeconomics is a discipline that melds the concepts and tools of economics, psychology,
and neuroscience to explore the neural substrates of economic choices. These data may be
central to understanding the choices made by individuals suffering from reinforcement
pathologies. For example, choices for the smaller, more immediate reinforcer were
associated with relatively high levels of activation in parts of the limbic system, whereas
choices for the larger, later reinforcer were associated with relatively high levels of
activation in parts of the prefrontal cortex. These findings further enabled the development
of the competing neurobehavioral decision systems theory (hereafter referred to as
competing decision systems). The competing decision systems view posits that choices
between immediate and delayed reinforcers are related to the regulatory balance of
activation in two neural systems. (1) The evolutionarily older impulsive system, which
consists of portions of the limbic and paralimbic areas, is primarily involved in the valuation
of immediate rewards. And (2) the more recently developed executive system, which
consists of portions of the prefrontal cortices, is involved in the consideration of the future
and the selection of delayed rewards. According to this view, the rate that an individual
discounts delayed rewards reflects the relative strength of these two systems. Thus, the
patterns of responding associated with reinforcer pathologies (e.g. drug addiction) are
related to a hyperactive impulsive and/or a hypoactive executive system.
Evidence of the impulsive system’s role in valuation
Data suggest that a hyperactive impulsive system is involved in the pathological valuation of
immediate and/ or low-cost reinforcers.
Evidence of the impulsive system’s role in valuation
Evidence suggests that a hypoactive executive system is involved in pathological reinforcer
choice. The valuation of delayed reinforcers is related to activity in the executive system.
Decisions between reinforcers available at different costs result in increased levels of
activation in the executive system. The executive systems of individuals suffering from
reinforcer pathologies such as drug addiction typically have lower cortical volume and grey
matter density than do controls. lesions in the executive system result in substantial
impairments in decision making, such as the inability to change future behavior based on the
negative feedback provided for previous behaviour.
Manipulation of competing decision systems
The elevated impulsive system activation associated with deprivation disrupts the balance
between these competing decision systems, resulting in elevated rates of discounting.
Manipulating the executive system can have similar effects on delay discounting rates. For
example, discounting rates were higher when participants were required to concurrently
complete a working memory task. Thus, an executive system taxed through its concurrent
use in other tasks ineffectively competes with the impulsive system, resulting in elevated
rates of discounting.
Types of dysregulation
Individuals are at risk of developing reinforcer pathologies whenever the strength of the
impulsive system exceeds that of the executive system. There are several ways that the
executive and impulsive systems can be out of regulatory balance. For example, an individual
