Download Reinforcement & Drug Effects

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 drugtaking behavior ~

Operant Conditioning
SD
: B
SR
Classical vs. Operant Conditioning
SR
 biologically important stimulus
B
R
 Response  S
 SD
 Discriminative stimulus
R available
 Signals S
R ~
 Response required to obtain S

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 ~
Other Phenomena

Similar to classical conditioning
R
 acquisition: B  S

extinction: B  No SR

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 ~

Drug Self-administration

operant conditioning

Press bar  drug infusion ~
Drug
pump
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
R
 B  appetitive S
 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 ~

Mesolimbic Pathway
NA
MFB
Ventral
Tegmental Area
VTA
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
 Na3b4 (Ach-R)
 Modulates mesolimbic pathway
 18-MC (18-Methoxycoronaridine)
 Ibogaine derivative
 Na3b4 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? ~
