Transcript Addiction

Definitions
• Drug Use
– Taking a psychoactive substance for non-medical purposes, out of
curiosity
• Drug Abuse
– Drug use that leads to problems (e.g. loss of effectiveness in
society; behavioral psychopathology, criminal acts)
• Drug Dependence
– A maladaptive pattern of drug use leading to clinically-significant
impairment or distress, associated with difficulty in controlling
drug-taking behavior, withdrawal, and tolerance
– The state of needing a drug to function within ‘normal limits’
Nature of Addiction - a continuum of
use?
Loss of control 
However, addiction is more than mere drug use…
DSM-IV Criteria for Substance Dependence
A maladaptive pattern of substance use, leading to clinically significant impairment or distress, as
manifested by three (or more) of the following, occurring at any time in the same 12 month period:
•
•
Tolerance
Withdrawal
•
Substance taken in larger amounts or over a longer period than intended
•
Persistent desire or unsuccessful efforts to cut down or control substance use
•
Great deal of time spent in activities necessary to obtain substance, use
substance (e.g., chain smoking), or recover from effects
•
Important social, occupational, or recreational activities given up or reduced
because of substance use
•
Substance use continued despite knowledge of persistent or recurrent physical
or psychological problem likely to have been caused or exacerbated by
substance
Physical vs. Psychological Dependence
• Physical Dependence
– Withdrawal symptoms in the absence of the drug
– Tolerance to its effects with repeated use
• Psychological Dependence
– “a relatively extreme, pathological state in which obtaining, taking, and
recovering from a drug represents a loss of behavioral control over drug
taking which occurs at the expense of most other activities and despite
adverse consequences” (Altman et al)
– “a situation where drug procurement and administration appear to govern
the organism’s behavior, and where the drug seems to dominate the
organism’s motivational hierarchy” (Bozarth)
Classic Models of Addiction
Model
Emphasized Causes
Example Interventions
Moral
Personal responsibility; self- Moral suasion; social/legal
control
sanctions
Spiritual
Spiritual defect
Prayer; 12-step faith-based
treatment (e.g. AA)
Temperance
Drugs
Control of supply; calls for
abstinence
Educational
Ignorance
Education
Conditioning
Classical/operant
conditioning
Counterconditioning;
extinction
Classic Models of Addiction continued
Model
Emphasized Causes
Example Interventions
Biological
Heredity; brain physiology;
self-medication
Risk identification; calls for
abstinence; medical treatment
Psychodynamic
Personality; defense
mechanisms
Psychoanalysis
Family
Dynamics
Family dysfunction
Family therapy
Social
Learning
Modeling; expectancies
Positive role models; rational
restructuring of expectancies
Sociocultural Environmental; cultural;
economic
Social policy; social services
Physical Dependence or Withdrawal Model
(Negative Reinforcement)
• Some drugs produce physical dependence and withdrawal
symptoms upon cessation of drug-taking.
– Withdrawal symptoms are produced by the body in order to
compensate for the unusual effects of the drug.
– Withdrawal symptoms are generally the opposite of the effect
produced by the drug.
• Addicts continue to use drugs in order to avoid withdrawal.
• Over time, drugs no longer have the same rewarding
effects - they merely allow the person to feel “normal.”
Inadequacies of Withdrawal Model
• Not all abused drugs generate withdrawal symptoms
(cocaine, amphetamine).
• Different drugs produce different withdrawal symptoms
with different neural bases.
• Once dependent you should continue taking drug, but
people spontaneously stop.
• Once drug-abstinent, users should not relapse since
motivation has disappeared, but they do.
• No explanation as to why people take drugs in the first
place.
Positive Incentive (Hedonic) Models
(Positive Reinforcement)
• Drugs produce pleasure - a “high.”
• Some drugs provide indirect positive incentive they disinhibit behavior that is normally
suppressed (e.g., alcohol and social skills).
• Most drugs of abuse stimulate the brain’s reward
circuits.
– All known drugs of abuse stimulate release of DA/opioids in the
nucleus accumbens
– Animals will work to micro-inject drugs of abuse and electrically
stimulate the same parts of the brain
– Normal rewards (food, drink, sex) also stimulate DA release
Animal Models of Reinforcement (cont.)
• Self-administration
– Animals work for reinforcing
drugs (IV, oral, inhalant)
– Schedules of reinforcement
(fixed, progressive ratio)
DA release following VTA stimulation
Drugs that are and are not self
administered by animals
•
•
•
•
•
•
•
•
•
•
Alcohol
Amphetamine
Barbiturates
Caffeine
Cocaine
Nicotine
Opiates
Procaine (n.a. by humans)
PCP
THC
•
•
•
•
Imipramine
Mescaline (abused by humans)
Phenothiazines
Scopolamine
Drug Dependence Among Ever-Users
Tobacco
Heroin
Cocaine
Alcohol
Stimulants
Marihuana
0
10
20
% Dependent
30
40
Opponent Process Model
(Solomon, 1977)
• Drug-use initially motivated by positive reinforcement
• Over time, tolerance to rewarding effects, but abstinence leads to
withdrawal
• Drug use ultimately maintained by negative reinforcement
Current Traditional View
(based on opponent process model)
• Initiation of drug taking is primarily driven by anticipated pleasure
(facilitated by peer pressure, social facilitation, curiosity).
• For most drugs, pleasure becomes primary motivator and drug craving
becomes cued by drug related stimuli.
• For some drugs (e.g., alcohol, cocaine, heroin) pleasure is enhanced by
reversing unpleasant aspects of normal life.
• For some drugs (e.g., nicotine, caffeine, heroin, alcohol), drug-taking
leads to dependence and withdrawal which adds additional motivation
to continue drug-taking habit and makes “giving up” difficult.
• This withdrawal state can also be associated with environmental cues,
and increases the tendency for relapse.
Limitations of Opponent Process Models
• Drug withdrawal is much less powerful at
motivating drug-taking behavior
– stress seems to be more powerful
• Withdrawal symptoms are maximal within a few
days after cessation of drug use, but susceptibility
to relapse continues to grow for weeks to months.
• Cues typically fail to elicit conditionedwithdrawal.
• Craving is different from withdrawal.
Aberrant Learning
(beyond pleasure and pain)
• Cues that predict the availability of rewards can
powerfully activate DA circuitry in both animals
and humans (Schultz, 1998), sometimes even
better than the reward itself.
• Therefore, the transition to addiction results from
the ability of drugs to promote this type of
aberrant learning.
Monkey VTA Study (Schultz et al, 1990s)
• Monkeys classically-conditioned to
associate light with food
• After learning, VTA neurons
increase firing to light instead of
food
• Decreased firing if light-cued food
doesn’t appear
• Baseline DA = expected reward
• Increased firing = better than
expected
• Reduced firing = worse than
expected
Problems with Aberrant Learning Models
• Most have focused at the level of neuronal
systems
• Few have provided a psychological step-by-step
account of how aberrant learning could actually
produce addiction.
– Are the associations S-S or S-R learning? are they
explicit or implicit?
Implicit Learning (Tiffany, 1990)
– Drug-taking habits are caused by aberrant learning,
because drugs subvert neuronal mechanisms involved
in implicit learning (unconscious S-R or S-S processes).
Urges and cravings are of secondary importance to
force of habit (automaticity).
– “…with sufficient practice, performance on any task
can become automatic…” and “drug-use behavior in
the addict represent one such activity, controlled largely
by automatic processes”
– Over-learned habits become so automatic that they
essentially become compulsive
Problems with Automaticity Models
• They mistake automatic performance for
motivational compulsion.
– Habits (brushing teeth, driving) are not intrinsically
compulsive, no matter how automatic they are
– Would you sacrifice your home, your job, your friends
to engage in teeth brushing behavior?
• Many aspects of addictive drug pursuit are flexible
and not habitual
Incentive –Sensitization Model
(Robinson and Berridge, 1993)
• Addictive drugs produce long-lasting changes in
brain organization
• The brain systems that are changed include those
normally involved in the process of incentive
motivation and reward.
• Addiction renders these systems hypersensitive
(“sensitized”) to drugs and drug-associated stimuli
• These sensitized systems mediate a component of
reward termed incentive salience or “wanting”
(not pleasure or “liking”).
Incentive Sensitization
• Drug-induced sensitization of brain systems (DA) that
mediate incentive-salience causes drugs and drugassociated stimuli to become compulsively “wanted”
• The activation of the sensitized system can occur both
implicitly or explicitly
• These systems can be dissociated from neural systems that
mediate the hedonic effects of drugs (opioids), i.e., how
much they are “liked” (wanting is not liking).
Psychomotor Sensitization
• Many drugs produce psychomotor-activating
effects
– amphetamines, cocaine, opiates, alcohol, nicotine,
MDMA
• These effects last from months to years after drug
use is discontinued
• Some individuals sensitize readily, whereas others
are more resistant (may explain susceptibility to
addiction)
– genes, hormones, stress hormones, past trauma…?
– stress causes sensitization and may bias addiction
– addiction may make an individual hypersensitive to stress
Incentive-Sensitization Model
• Addiction may be triggered by drug cues as a
“learned” motivational response but it is not a
disorder of aberrant learning per se
• It is a disorder of aberrant incentive motivation
due to drug induced sensitization of neural
systems that attribute salience to particular stimuli.
Cocaine Cues Study (Grant et al, 1996)
• PET = Positron Emission Tomography
• Radioactive marker injected
• Scanner detects light waves from decay
Cocaine Study continued
• Cocaine addicts and
controls shown cocaine
cues and neutral cues
• Cocaine cues in addicts
elicited craving, brain
activation
• Activation correlated with
craving in Dorsolateral
Prefrontal Cortex,
Amygdala, Cerebellum
Smoking Stroop Study (Gross et al, 1993)
• Normal Stroop effect:
takes longer to name ink
color when incongruent
with word
• Smoking Stroop: 12-hour
abstinent smokers take
longer to name ink color
for smoking words than
neutral words
Congruent
Incongruent
RED
BLUE
GREEN
RED
BLUE
GREEN
Smoking
Neutral
MATCH
SMOKE
PACK
BOARD
PAINT
BRUSH
Impairments in Frontocortical Function
• May be responsible for “irrational” behavior of
addicts
• Poor decision-making
• May exacerbate incentive-sensitization