Reinforcement& Drug Effects

Lesson 15

Operant Conditioning

Acquisition & Maintenance of behavior important for survival Response Consequences

Response followed by satisfying outcome likely to be repeated

Acquisition & maintenance of drug-taking behavior ~

Operant Conditioning

SD B SR:

Classical vs. Operant Conditioning

SR biologically important stimulus

B Response SR

SD

Discriminative stimulus Signals SR available Response required to obtain SR ~

Reinforcement Strengthens behavior

increases responding Positive reinforcement

B appetitive stimulus Negative reinforcement

B terminates aversive stimulus or prevents

Both are desirable outcomes ~

Punishment Weakens behavior

decreases responding Positive punishment

B aversive stimulus Negative punishment

B terminates appetitive stimulus or prevents

Both are undesirable outcomes ~

What are reinforcers? Primary reinforcers

biologically important stimuli Appetitive

food water sexual pleasure drugs

Aversive pain Illness ~

Reinforcers (continued) Secondary reinforcers

money praise drug paraphernalia

How do they become reinforcers? Classical Conditioning

paired with primary reinforcers starts as a CS or SD

requires learning ~

Similar to classical conditioning acquisition: B SR

extinction: B No SR

Other Phenomena

spontaneous recovery

disinhibition

reacquisition

including magnitude & delay of RFT ~

Drug Self-administration (SA)

Animal model: drug taking behavior Operant conditioning

Involves both... Reward (positive RFT) & escape/avoidance (negative RFT)

Self-administer same drugs as humans Screening new drugs as potential

reinforcers ~

Drugpump

Drug Self-administration

operant conditioning

Press bar drug infusion ~

Drugs as reinforcers

Addictive drugs Postive reinforcers Negative reinforcers Aversive aftereffects

Obey laws of learning same as any other learned response ~

Alcohol (ethanol)

Positive RFT Pleasant feeling

Negative RFT Reduces withdrawal effects reduces stress

Aversive aftereffects Hangover = withdrawal ~

Why does drinking persist?

Hangover as effective punishment? Delay of RFT

Reward immediate Punishment long delay

Magnitude of RFT Smoking crack vs snorting cocaine

Greater euphoria & shorter delay faster acquisition & slower extinction ~

Biological Bases of Drug Reinforcement

Reinforcement Mechanisms

Positive reinforcement B appetitive SR

Mesolimbic Pathway Negative Reinforcement

Widely distributed Depends of specific drug effects ~

Reward Mechanisms

Olds & Milner ESB

Mesolimbic Pathway Ventral Tegmental Area (VTA) Medial Forebrain Bundle (MFB) Nucleus Accumbens (NA)

Role of Dopamine Evaluating rewarding effects of drugs ~

The “Pleasure Center” of the Brain

Nucleus accumbens (NA) DA activity mediates reward DA activity in NA “pleasure”

Site of action for positive reinforcers Natural reinforcers Drugs ~

MFB

Ventral Tegmental Area

VTA

Mesolimbic Pathway

NA

More evidence for dopamine role Agonist: increases effects of NT DA agonist euphoria

cocaine, amphetamine Heroin opioids DA in NA

via Ventral Tegmental Area (VTA) most addictive drugs

DA antagonists Blocks learning Also blocks responding for food ~

Alternate Reward Pathway

Medial Habenula Habenulo-interpeduncular pathway N34 (Ach-R) Modulates mesolimbic pathway

18-MC (18-Methoxycoronaridine) Ibogaine derivative N34 antagonist Stops self-administration ~

Negative Reinforcement

2 classes B terminates aversive state

Therapeutic e.g. morphine relieves pain Alcohol relieves anxiety self-medication

Escape/avoidance of drug withdrawal Following tolerance/dependence ~

Negative Reinforcement Different withdrawal syndromes

e.g. depressants vs stimulants Depends on drugs effects

Tolerance as compensatory responses Abstention: deficient synaptic activity Withdrawal

More drug restores system balance Aversive effects ~

Negative Reinforcement Role of Nucleus Accumbens?

Rada, Mark & Hoebel (1998) Medial Hypothalamus

stimulation aversive state press bar terminate stimulation

Negative reinforcement dopamine in NA by 100%

Neg RFT blocked by DA antagonist? ~