drugs and addiction. what is a drug? –an exogenous substance that, when absorbed into the body of...

Drugs and AddictionDrugs and Addiction

Drugs and AddictionDrugs and Addiction

What is a drug?What is a drug?– An exogenous substance that, when absorbed into the body of a An exogenous substance that, when absorbed into the body of a

living organism, alters normal bodily functionliving organism, alters normal bodily function

What are psychoactive drugs?What are psychoactive drugs?– Drugs that influence subjective experience and behavior by Drugs that influence subjective experience and behavior by

acting on the nervous systemacting on the nervous system

How are drugs administered?How are drugs administered?– Drugs are typically administered in one of four ways:Drugs are typically administered in one of four ways:

Oral Ingestion (e.g. alcohol)Oral Ingestion (e.g. alcohol)Injection (e.g. heroin)Injection (e.g. heroin)Inhalation (e.g. tobacco)Inhalation (e.g. tobacco)Absorption through Mucous Membranes (e.g. cocaine)Absorption through Mucous Membranes (e.g. cocaine)

Mechanisms of Drug ActionMechanisms of Drug Action

Psychoactive Drugs Psychoactive Drugs influence the CNS is influence the CNS is many ways, including:many ways, including:

– Binding to pre- and Binding to pre- and postsynaptic receptorspostsynaptic receptors

– Influencing synthesis, Influencing synthesis, transport, release, or transport, release, or deactivation of deactivation of neurotransmittersneurotransmitters

– Influencing the chain of Influencing the chain of chemical reactions chemical reactions elicited by the activation elicited by the activation of postsynaptic receptorsof postsynaptic receptors

Drug MetabolismDrug Metabolism

Most drugs are deactivated by enzymes synthesized by Most drugs are deactivated by enzymes synthesized by the liver.the liver.

– Drug MetabolismDrug MetabolismProcess by which liver enzymes covert active drugs to non-active Process by which liver enzymes covert active drugs to non-active forms.forms.Typically enzymes covert drugs into a more hydrophilic form, Typically enzymes covert drugs into a more hydrophilic form, preventing the drug from being able to pass through the lipid preventing the drug from being able to pass through the lipid membranes of cells.membranes of cells.

– Drug EliminationDrug EliminationSmall amounts of some psychoactive drugs are passed out of Small amounts of some psychoactive drugs are passed out of the body in urine, sweat, feces, breath, and mother’s milkthe body in urine, sweat, feces, breath, and mother’s milk

Drug ToleranceDrug Tolerance


State of decreased sensitivity to a drug that develops as a result State of decreased sensitivity to a drug that develops as a result of exposure to it.of exposure to it.

Drug tolerance can be shown in two ways:Drug tolerance can be shown in two ways:

– A given dose of a drug has LESS of an effect than that A given dose of a drug has LESS of an effect than that before exposure to it.before exposure to it.

– A HIGHER dose of a drug is required to produce the same A HIGHER dose of a drug is required to produce the same effect.effect.


Drug ToleranceDrug Tolerance– A shift of the dose-response curve (fig. 15.1) to the right.A shift of the dose-response curve (fig. 15.1) to the right.


Cross ToleranceCross Tolerance– One drug can produce tolerance to other drugs that act by the One drug can produce tolerance to other drugs that act by the

same mechanismssame mechanisms

Drug SensitizationDrug Sensitization– Increasing sensitivity to a drugIncreasing sensitivity to a drug

A given dose of a drug has MORE of an effect than it had A given dose of a drug has MORE of an effect than it had before exposure to it.before exposure to it.

A LOWER dose of a drug is required to produce the same A LOWER dose of a drug is required to produce the same effect.effect.


Drug SensitizationDrug Sensitization– A shift of the dose-response curve (fig. 15.1) to the left.A shift of the dose-response curve (fig. 15.1) to the left.


Metabolic ToleranceMetabolic Tolerance– Drug tolerance that results from changes that reduce the amount of Drug tolerance that results from changes that reduce the amount of

the drug getting to its sites of action.the drug getting to its sites of action.E.g. liver increases the production of enzymes that metabolize a E.g. liver increases the production of enzymes that metabolize a drugdrug

Functional ToleranceFunctional Tolerance– Drug tolerance that results from changes that reduce the reactivity of Drug tolerance that results from changes that reduce the reactivity of

the sites of action to the drug.the sites of action to the drug.E.g. reduction in the number of receptors for a drugE.g. reduction in the number of receptors for a drug

– Tolerance to psychoactive drugs is largely Tolerance to psychoactive drugs is largely functionalfunctional

Drug WithdrawalDrug Withdrawal

Withdrawal SyndromeWithdrawal Syndrome

– Occurs when significant amounts of a drug that have been in the Occurs when significant amounts of a drug that have been in the body for a period of time suddenly decrease.body for a period of time suddenly decrease.

E.g. long-time smokers attempt to quit by going “cold turkey.”E.g. long-time smokers attempt to quit by going “cold turkey.”

– Withdrawal effects are opposite the initial effects of the drug (fig. Withdrawal effects are opposite the initial effects of the drug (fig. 15.2).15.2).

– Individuals that suffer withdrawal reactions when they stop taking a Individuals that suffer withdrawal reactions when they stop taking a drug aredrug are Physically Dependent.Physically Dependent.

Role of Learning in Drug Role of Learning in Drug ToleranceTolerance

Contingent Drug ToleranceContingent Drug Tolerance

– Tolerance develops only to drug effects that are actually Tolerance develops only to drug effects that are actually experienced.experienced.


Conditioned Drug ToleranceConditioned Drug Tolerance

– Tolerance effects are maximally expressed only when a drug is Tolerance effects are maximally expressed only when a drug is administered in the same situation in which it has previously been administered in the same situation in which it has previously been administered.administered.

Group A – tested in Group A – tested in different context as different context as drug administrationdrug administration

Group B – tested in Group B – tested in same context as same context as drug administrationdrug administration


Conditioned Drug ToleranceConditioned Drug Tolerance

– Tolerance effects are maximally expressed only when a drug is Tolerance effects are maximally expressed only when a drug is administered in the same situation in which it has previously been administered in the same situation in which it has previously been administered.administered.

Conditioned Compensatory ResponsesConditioned Compensatory Responses

– Stimuli that predict drug administration elicit conditional responses Stimuli that predict drug administration elicit conditional responses opposite the effects of the drug.opposite the effects of the drug.

Exteroceptive stimuliExteroceptive stimuliInteroceptive stimuliInteroceptive stimuli

– Views every drug administration as a Pavlovian conditioning trial.Views every drug administration as a Pavlovian conditioning trial.

Five Commonly Abused DrugsFive Commonly Abused Drugs

TobaccoTobacco

AlcoholAlcohol

MarijuanaMarijuana

Cocaine Cocaine

OpiatesOpiates


TobaccoTobacco

– NicotineNicotineThe major psychoactive ingredient of tobacco.The major psychoactive ingredient of tobacco.

– Stimulates nicotinic ACh receptors Stimulates nicotinic ACh receptors

Highly addictiveHighly addictive– About 70% of those who experiment with smoking become About 70% of those who experiment with smoking become

addicted.addicted.– Compare to 10% with alcohol and 30% for heroinCompare to 10% with alcohol and 30% for heroin

Only about 20% of attempts to stop smoking are successful.Only about 20% of attempts to stop smoking are successful.

TobaccoTobacco

Effects of Long-Term Tobacco UseEffects of Long-Term Tobacco Use

– Smoker’s syndrome – chest pain, labored breathing, wheezing, Smoker’s syndrome – chest pain, labored breathing, wheezing, coughing, increased susceptibility to respiratory infectionscoughing, increased susceptibility to respiratory infections

– Susceptible to various lethal lung disorders – pneumonia, bronchitis, Susceptible to various lethal lung disorders – pneumonia, bronchitis, emphysema, lung canceremphysema, lung cancer

– Buerger’s diseaseBuerger’s disease

– Some good news: quitting smoking by age 40 adds an average of 9 Some good news: quitting smoking by age 40 adds an average of 9 years to life spanyears to life span


AlcoholAlcohol

– A depressantA depressant

– Heritability estimate for alcohol addiction is about 55%Heritability estimate for alcohol addiction is about 55%

– Metabolic and functional tolerance developsMetabolic and functional tolerance develops

– Attacks almost every tissue in the bodyAttacks almost every tissue in the body

AlcoholAlcohol

Effects of Chronic Alcohol ConsumptionEffects of Chronic Alcohol Consumption

– Severe withdrawal in three phases:Severe withdrawal in three phases:5-6 hrs post-drinking: tremors, nausea, sweating, vomiting, etc.5-6 hrs post-drinking: tremors, nausea, sweating, vomiting, etc.15-30 hrs: convulsive activity15-30 hrs: convulsive activity24-48 hrs: delirium tremens (DTs) – may last 3-4 days24-48 hrs: delirium tremens (DTs) – may last 3-4 days

– The convulsions and DTs can be fatalThe convulsions and DTs can be fatal

– Korsakoff’s syndromeKorsakoff’s syndrome

– CirrhosisCirrhosis

– Fetal alcohol syndromeFetal alcohol syndrome

AlcoholAlcohol

Alcohol and the BrainAlcohol and the Brain

– Reduces flow of Ca2+ into neuronsReduces flow of Ca2+ into neurons

– Interferes with 2nd messenger systemsInterferes with 2nd messenger systems

– Disrupts GABAergic and glutaminergic transmissionDisrupts GABAergic and glutaminergic transmission

– Triggers apoptosisTriggers apoptosis


MarijuanaMarijuana

– Cannabis sativa – common hemp plantCannabis sativa – common hemp plantTHC – primary psychoactive constituent – although over 80 THC – primary psychoactive constituent – although over 80 others are presentothers are present

– High doses impair short-term memory and interfere with tasks High doses impair short-term memory and interfere with tasks involving multiple stepsinvolving multiple steps

– Addiction potential is lowAddiction potential is low

– Negative effects of long-term use are far less severe than those Negative effects of long-term use are far less severe than those associated with alcohol and tobaccoassociated with alcohol and tobacco


MarijuanaMarijuana

– THC binds to endogenous cannabinoid receptors (CB receptors.)THC binds to endogenous cannabinoid receptors (CB receptors.)CB1 receptor is the most common G-protein linked receptor in CB1 receptor is the most common G-protein linked receptor in the brain.the brain.CB2 receptor is found in the brain stem and in cells in the CB2 receptor is found in the brain stem and in cells in the immune system.immune system.

– Cannabinoid receptors are found on pre-synaptic neurons!Cannabinoid receptors are found on pre-synaptic neurons!endocannabinoids are released from the post-synaptic neuron, endocannabinoids are released from the post-synaptic neuron, and bind to CB receptors on the pre-synaptic neuron, acting as a and bind to CB receptors on the pre-synaptic neuron, acting as a retrograde neurotransmitter.retrograde neurotransmitter.


MarijuanaMarijuana

MarijuanaMarijuana

Adverse Effects of Heavy Marijuana UseAdverse Effects of Heavy Marijuana Use

– Respiratory problems – cough, bronchitis, asthmaRespiratory problems – cough, bronchitis, asthma

– Single large doses can trigger heart attacks in susceptible Single large doses can trigger heart attacks in susceptible individualsindividuals

– No evidence that marijuana causes permanent brain damageNo evidence that marijuana causes permanent brain damage

– Possible correlation between marijuana use and schizophrenia, but Possible correlation between marijuana use and schizophrenia, but no causal link has been shownno causal link has been shown

MarijuanaMarijuana

Medicinal Uses of MarijuanaMedicinal Uses of Marijuana

– Treats nausea Treats nausea

– Blocks seizuresBlocks seizures

– Dilates bronchioles of asthmaticsDilates bronchioles of asthmatics

– Decreases severity of glaucomaDecreases severity of glaucoma

– Reduces some forms of painReduces some forms of pain


StimulantsStimulants

– Increase neural and behavioral activityIncrease neural and behavioral activity

– Cocaine, Amphetamine, MDMA – commonly abusedCocaine, Amphetamine, MDMA – commonly abused

– Crack – a potent, cheap, and smokable form of cocaineCrack – a potent, cheap, and smokable form of cocaine

– Cocaine is an effective local anestheticCocaine is an effective local anestheticSynthetic analogues procaine and lidocaine used todaySynthetic analogues procaine and lidocaine used today


CocaineCocaine

– Cocaine binges or sprees may lead to cocaine psychosisCocaine binges or sprees may lead to cocaine psychosisLooks like paranoid schizophreniaLooks like paranoid schizophrenia

– While tolerance may develop to some effects of cocaine, While tolerance may develop to some effects of cocaine, sensitization is seen to motor and convulsive effectssensitization is seen to motor and convulsive effects

– Although highly addictive, withdrawal is relatively mildAlthough highly addictive, withdrawal is relatively mild


CocaineCocaine

– Blocks the re-uptake of dopamine by the dopamine re-uptake Blocks the re-uptake of dopamine by the dopamine re-uptake transportertransporter


Other StimulantsOther Stimulants

– Stimulants are neurotoxinsStimulants are neurotoxins

– Amphetamine (“speed”)Amphetamine (“speed”)

Effects like cocaine – can produce psychosisEffects like cocaine – can produce psychosis

– MDMA (“ecstasy”)MDMA (“ecstasy”)

Impairs dopaminergic and serotonergic function in animal Impairs dopaminergic and serotonergic function in animal studies; human relevance unclearstudies; human relevance unclear

Impairs executive function, inhibitory control, and decision Impairs executive function, inhibitory control, and decision making (as shown by cortex and limbic functional brain scan making (as shown by cortex and limbic functional brain scan abnormalities) abnormalities)


Opiates: Heroin and MorphineOpiates: Heroin and Morphine

– The endogeneous chemicals that bind to opiate receptors are called The endogeneous chemicals that bind to opiate receptors are called endorphinsendorphins, and there are at least 20 different kinds of endorphins., and there are at least 20 different kinds of endorphins.

– Morphine and codeine, which also bind to these receptors, are drugs Morphine and codeine, which also bind to these receptors, are drugs obtained from the opium poppyobtained from the opium poppy

– Medicinal usesMedicinal uses

Analgesics (painkillers)Analgesics (painkillers)

Treatment of cough and diarrheaTreatment of cough and diarrhea

– High risk of addictionHigh risk of addiction


U.S. Opiate HistoryU.S. Opiate History

– Opium was readily available in a variety of “potions” until 1914Opium was readily available in a variety of “potions” until 1914

– Harrison Narcotic Act (1914) Harrison Narcotic Act (1914) Illegal to sell or use opium Illegal to sell or use opium Heroin, a synthetic opiate, was still legalHeroin, a synthetic opiate, was still legal

– Structure similar to morphine, but better able to cross the Structure similar to morphine, but better able to cross the blood-brain barrier blood-brain barrier

– More addictiveMore addictive

– Heroin illegal as of 1924Heroin illegal as of 1924


Treatment for Heroin AddictionTreatment for Heroin Addiction

– Opiates bind to endorphin receptorsOpiates bind to endorphin receptors

– Methadone binds to these receptorsMethadone binds to these receptorsProduces less pleasureProduces less pleasureAdministered orally Administered orally Prevents withdrawal Prevents withdrawal

– Buprenorphine – similar to methadone but longer lastingBuprenorphine – similar to methadone but longer lasting

– Substituting a less dangerous drug for the abused drugSubstituting a less dangerous drug for the abused drug


Prevalence of drug use in the United StatesPrevalence of drug use in the United States

Reducing Drug AbuseReducing Drug Abuse

Current approaches (e.g. War on Drugs) are not effectiveCurrent approaches (e.g. War on Drugs) are not effective

What recommendations would you make to decrease the What recommendations would you make to decrease the incidence of drug abuse?incidence of drug abuse?

Which abused drugs should we be most concerned about?Which abused drugs should we be most concerned about?

AddictionAddiction

What is addiction?What is addiction?

– Habitual drug use despite its adverse effects on health, social life, Habitual drug use despite its adverse effects on health, social life, and despite repeated efforts to stop.and despite repeated efforts to stop.

Drug addicts are habitual drug users.Drug addicts are habitual drug users.Not all habitual drug users are addicts.Not all habitual drug users are addicts.

Is addiction the same thing as physical dependence?Is addiction the same thing as physical dependence?– NO!NO!– Drug addicts will renew drug taking even after withdrawal effects Drug addicts will renew drug taking even after withdrawal effects

have subsided.have subsided.

Biopsychological Theories of Biopsychological Theories of AddictionAddiction

Physical-dependence theory Physical-dependence theory

– dependence due to pain of withdrawaldependence due to pain of withdrawal– Addicts caught in a cycle of drug taking, withdrawal, drug taking Addicts caught in a cycle of drug taking, withdrawal, drug taking

to relieve withdrawal.to relieve withdrawal.– Detoxified addictsDetoxified addicts

No longer have drugs in their system and do not experience No longer have drugs in their system and do not experience withdrawal symptomswithdrawal symptoms

does not explain why…does not explain why…– addicts relapse long after detoxificationaddicts relapse long after detoxification– individuals begin using drugsindividuals begin using drugs– addictions develop to drugs that do not produce severe addictions develop to drugs that do not produce severe

withdrawal symptomswithdrawal symptoms


Positive-incentive theories Positive-incentive theories

– The primary factor in most cases of addiction is the craving for a The primary factor in most cases of addiction is the craving for a drug’s pleasurable effects.drug’s pleasurable effects.

must explain…must explain…– the difference between the hedonic value and the positive the difference between the hedonic value and the positive

incentive value of the drugincentive value of the drug– the transition from being a drug user to becoming a drug addictthe transition from being a drug user to becoming a drug addict


Incentive-sensitization theory Incentive-sensitization theory

– Positive-incentive value (wanting) Positive-incentive value (wanting) the anticipated pleasure of taking a drugthe anticipated pleasure of taking a drug

– Hedonic value (liking)Hedonic value (liking)the actual pleasure experiencedthe actual pleasure experienced

– With drug use, the positive-incentive value increases due to memory With drug use, the positive-incentive value increases due to memory of the pleasure of early drug experienceof the pleasure of early drug experience

– The hedonic value decreases due to drug toleranceThe hedonic value decreases due to drug tolerance

– Result: addicts crave drugs more and enjoy them lessResult: addicts crave drugs more and enjoy them less

Causes of RelapseCauses of Relapse

Stress Stress – drug use as a coping mechanismdrug use as a coping mechanism

PrimingPriming – a single exposure leads to a relapsea single exposure leads to a relapse

Environmental cuesEnvironmental cues– Conditioned drug toleranceConditioned drug tolerance– Returning to place where drugs once taken (or even thinking about Returning to place where drugs once taken (or even thinking about

drug) causes conditioned compensatory responses, craving, and drug) causes conditioned compensatory responses, craving, and relapserelapse

Reward CircuitsReward Circuits

– Brain circuitry exists that reinforces behaviors Brain circuitry exists that reinforces behaviors

– Many species will work for stimulation of brain “pleasure centers”Many species will work for stimulation of brain “pleasure centers”

– Discovered by Olds and Milner (1954)Discovered by Olds and Milner (1954)Proposed that the same brain regions are activated by natural Proposed that the same brain regions are activated by natural rewards, such as food, water, and sex.rewards, such as food, water, and sex.

– Drug use may be reinforced by acting on this circuitryDrug use may be reinforced by acting on this circuitry

Intracranial Self-Stimulation and Intracranial Self-Stimulation and Brain “Pleasure Centers” Brain “Pleasure Centers”

Intracranial Self-Stimulation (ICSS)

Fig. 15.6 A rat pressing a lever to obtain rewarding brain stimulation

Mesotelencephalic Dopamine Mesotelencephalic Dopamine System and Self-StimulationSystem and Self-Stimulation

Dopaminergic neurons projecting from two midbrain Dopaminergic neurons projecting from two midbrain areas to telencephalon areas to telencephalon

– Nigrostriatal pathwayNigrostriatal pathwaySubstantia nigra neurons projecting to dorsal striatumSubstantia nigra neurons projecting to dorsal striatum

– Mesocorticolimbic pathwayMesocorticolimbic pathwayVentral tegmental area neurons projecting to cortical and Ventral tegmental area neurons projecting to cortical and limbic sites, including the nucleus accumbenslimbic sites, including the nucleus accumbensThis is the major “reward” pathway for ICSS, natural This is the major “reward” pathway for ICSS, natural rewards, and addictive drugsrewards, and addictive drugs

Fig. 15.7 Mesotelencephalic dopamine system of the human brain

Mesocorticolimbic Pathway and Mesocorticolimbic Pathway and Reward Reward

Evidence that the mesotelencephalic pathway plays an Evidence that the mesotelencephalic pathway plays an important role in ICSS. important role in ICSS. – Self-stimulation sites that do not contain dopaminergic neurons Self-stimulation sites that do not contain dopaminergic neurons

project to the mesotelencephalic dopamine systemproject to the mesotelencephalic dopamine system

– Increase in dopamine release seen in the mesocorticolimbic pathway Increase in dopamine release seen in the mesocorticolimbic pathway following self-stimulation (fig. 15.8).following self-stimulation (fig. 15.8).

– Dopamine agonists tend to increase self-stimulation and antagonists Dopamine agonists tend to increase self-stimulation and antagonists to decrease self-stimulationto decrease self-stimulation

– Lesions of the mesocorticolimbic pathway disrupt self-stimulationLesions of the mesocorticolimbic pathway disrupt self-stimulation

Two Ways to Measure Drug Two Ways to Measure Drug Positive Incentive in AnimalsPositive Incentive in Animals

Drug self-administration paradigmDrug self-administration paradigm– Lab animals press a lever to inject drugs into themselves Lab animals press a lever to inject drugs into themselves

through cannulas (thin tubes) implanted in the brainthrough cannulas (thin tubes) implanted in the brain

Conditioned place-preferenceConditioned place-preference paradigmparadigm– Lab animals choose to spend more time in the cage Lab animals choose to spend more time in the cage

compartment where drugs were administered, compared to a compartment where drugs were administered, compared to a compartment not associated with drug administration.compartment not associated with drug administration.

Behavioral Preference TestsBehavioral Preference Tests

Fig. 15.9

Evidence of the Involvement of Dopamine in Drug Evidence of the Involvement of Dopamine in Drug AddictionAddiction

– Dopamine’s role suggested by self-stimulation studiesDopamine’s role suggested by self-stimulation studies

– Dopamine antagonists interfere with self-stimulation and reduce Dopamine antagonists interfere with self-stimulation and reduce the reinforcing effects of foodthe reinforcing effects of food

– Nucleus accumbens appears to play a primary roleNucleus accumbens appears to play a primary role

Dopamine and Drug Addiction

Nucleus Accumbens (NA) and Nucleus Accumbens (NA) and Drug AddictionDrug Addiction

Evidence of the Involvement of the Nucleus Accumbens Evidence of the Involvement of the Nucleus Accumbens in Drug Addictionin Drug Addiction

– Animals self-administer microinjections of addictive drugs into NAAnimals self-administer microinjections of addictive drugs into NA

– Microinjection of drugs into NA produce conditioned placed Microinjection of drugs into NA produce conditioned placed preferencespreferences

– Lesion NA or ventral tegmental area – no drug self-administration or Lesion NA or ventral tegmental area – no drug self-administration or drug-related place preferencedrug-related place preference

– Both self-administration of addictive drugs and natural reinforcers Both self-administration of addictive drugs and natural reinforcers result in increased dopamine in the NAresult in increased dopamine in the NA

Dopamine release: Reward or Dopamine release: Reward or Expectation of Reward?Expectation of Reward?

Reward:Reward:Ventral tegmental neurons fire in response to a stimulus at a rate Ventral tegmental neurons fire in response to a stimulus at a rate proportional to its reward valueproportional to its reward value

Expectation of Reward:Expectation of Reward:Neutral stimuli that predict a reward can trigger dopamine Neutral stimuli that predict a reward can trigger dopamine release in the NArelease in the NA

Current view:Current view:An increase in the activity of dopaminergic neurons in the ventral An increase in the activity of dopaminergic neurons in the ventral tegmental area occurs:tegmental area occurs:

– when a conditional stimulus predicts a reward when a conditional stimulus predicts a reward – when a reward is presented in an unpredictable fashionwhen a reward is presented in an unpredictable fashion

Structures That Mediate Structures That Mediate Addiction: The Current ViewAddiction: The Current View

Initial drug takingInitial drug taking– involves activation of the mesocorticolimbic pathway (nucleus involves activation of the mesocorticolimbic pathway (nucleus

accumbens), prefrontal lobes, and amygdalaaccumbens), prefrontal lobes, and amygdala

Craving and compulsive drug useCraving and compulsive drug use– Involves activation of the dorsal striatum and hypothalamic stress circuitsInvolves activation of the dorsal striatum and hypothalamic stress circuits

RelapseRelapse– stress (hypothalamic stress circuits)stress (hypothalamic stress circuits)– priming doses (prefrontal cortex)priming doses (prefrontal cortex)– drug associated cues (amygdala)drug associated cues (amygdala)

drugs and addiction. what is a drug? –an exogenous substance that, when absorbed into the body of...

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