Reinforcement

1
Reinforcement Drug Effects

• Lecture 14

2
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
  

3
Operant Conditioning

SD
B
SR
4
Classical vs. Operant Conditioning

• SR
• biologically important stimulus
• B
• Response ? SR
• SD
• Discriminative stimulus
• Signals SR available
• Response required to obtain SR

5
Reinforcement

• Strengthens behavior
• increases responding
• Positive reinforcement
• B ? appetitive stimulus
• Negative reinforcement
• B ? terminates aversive stimulus
• or prevents
• Both are desirable outcomes

6
Punishment

• Weakens behavior
• decreases responding
• Positive punishment
• B ? aversive stimulus
• Negative punishment
• B ? terminates appetitive stimulus
• or prevents
• Both are undesirable outcomes

7
What are reinforcers?

• Primary reinforcers
• biologically important stimuli
• Appetitive
• food
• water
• sexual pleasure
• drugs
• Aversive
• pain
• Illness

8
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

9
Other Phenomena

• Similar to classical conditioning
• acquisition B ? SR
• extinction B ? No SR

• spontaneous recovery
• disinhibition
• reacquisition
• including magnitude delay of RFT

10
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

11
Drug Self-administration
Drug pump

• operant conditioning
• Press bar ? drug infusion

12
Drugs as reinforcers

• Addictive drugs
• Postive reinforcers
• Negative reinforcers
• Aversive aftereffects
• Obey laws of learning
• same as any other learned response

13
Alcohol (ethanol)

• Positive RFT
• Pleasant feeling
• Negative RFT
• Reduces withdrawal effects
• reduces stress
• Aversive aftereffects
• Hangover withdrawal

14
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

15
Biological Bases of Drug Reinforcement
16
Reinforcement Mechanisms

• Positive reinforcement
• B ? appetitive SR
• Mesolimbic Pathway
• Negative Reinforcement
• Widely distributed
• Depends of specific drug effects

17
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

18
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

19
Mesolimbic Pathway
NA
MFB
VTA
20
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

21
Alternate Reward Pathway

• Medial Habenula
• Habenulo-interpeduncular pathway
• Na3b4 (Ach-R)
• Modulates mesolimbic pathway
• 18-MC (18-Methoxycoronaridine)
• Ibogaine derivative
• Na3b4 antagonist
• Stops self-administration

22
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

23
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

24
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?