Reinforcement & Drug Effects Lesson 15

Operant Conditioning n Acquisition & Maintenance of behavior l important for survival l Response Consequences n Response followed by satisfying outcome l likely to be repeated n Acquisition & maintenance of drug- taking behavior ~

Operant Conditioning SDSD BSRSR :

Classical vs. Operant Conditioning nSRnSR l biologically important stimulus nBnB l Response  S R nSDnSD l Discriminative stimulus l Signals S R available l Response required to obtain S R ~

Reinforcement n Strengthens behavior l increases responding n Positive reinforcement l B  appetitive stimulus n Negative reinforcement l B  terminates aversive stimulus l or prevents n Both are desirable outcomes ~

Punishment n Weakens behavior l decreases responding n Positive punishment l B  aversive stimulus n Negative punishment l B  terminates appetitive stimulus l or prevents n Both are undesirable outcomes ~

What are reinforcers? n Primary reinforcers l biologically important stimuli n Appetitive l food l water l sexual pleasure l drugs n Aversive l pain l Illness ~

Reinforcers (continued) n Secondary reinforcers l money l praise l drug paraphernalia n How do they become reinforcers? n Classical Conditioning l paired with primary reinforcers u starts as a CS or S D l requires learning ~

n Similar to classical conditioning l acquisition: B  S R l extinction: B  No S R Other Phenomena l spontaneous recovery l disinhibition l reacquisition l including magnitude & delay of RFT ~

Drug Self-administration (SA) n Animal model: drug taking behavior l Operant conditioning n Involves both... l Reward (positive RFT) l & escape/avoidance (negative RFT) n Self-administer same drugs as humans l Screening new drugs as potential reinforcers ~

Drug pump Drug Self-administration n operant conditioning n Press bar  drug infusion ~

Drugs as reinforcers n Addictive drugs l Postive reinforcers l Negative reinforcers l Aversive aftereffects n Obey laws of learning l same as any other learned response ~

Alcohol (ethanol) n Positive RFT l Pleasant feeling n Negative RFT l Reduces withdrawal effects l reduces stress n Aversive aftereffects l Hangover = withdrawal ~

Why does drinking persist? n Hangover as effective punishment? n Delay of RFT l Reward immediate l Punishment long delay n Magnitude of RFT n Smoking crack vs snorting cocaine l Greater euphoria & shorter delay l faster acquisition & slower extinction ~

Biological Bases of Drug Reinforcement

Reinforcement Mechanisms n Positive reinforcement l B  appetitive S R l Mesolimbic Pathway n Negative Reinforcement l Widely distributed l Depends of specific drug effects ~

Reward Mechanisms n Olds & Milner l ESB n Mesolimbic Pathway l Ventral Tegmental Area (VTA) l Medial Forebrain Bundle (MFB) l Nucleus Accumbens (NA) n Role of Dopamine n Evaluating rewarding effects of drugs ~

The “Pleasure Center” of the Brain n Nucleus accumbens (NA) l DA activity mediates reward  DA activity in NA  “pleasure” n Site of action for positive reinforcers l Natural reinforcers l Drugs ~

MFB Ventral Tegmental Area VTA Mesolimbic Pathway NA

More evidence for dopamine role n Agonist: increases effects of NT n DA agonist  euphoria l cocaine, amphetamine n Heroin  opioids   DA in NA l via Ventral Tegmental Area (VTA) l most addictive drugs n DA antagonists l Blocks learning l Also blocks responding for food ~

Alternate Reward Pathway n Medial Habenula l Habenulo-interpeduncular pathway N  3  4 (Ach-R) l Modulates mesolimbic pathway n 18-MC (18-Methoxycoronaridine) l Ibogaine derivative N  3  4 antagonist l Stops self-administration ~

Negative Reinforcement n 2 classes l B terminates aversive state n Therapeutic l e.g. morphine relieves pain l Alcohol relieves anxiety l self-medication n Escape/avoidance of drug withdrawal l Following tolerance/dependence ~

Negative Reinforcement n Different withdrawal syndromes l e.g. depressants vs stimulants l Depends on drugs effects n Tolerance as compensatory responses l Abstention: deficient synaptic activity l Withdrawal n More drug restores system balance l  Aversive effects ~

Negative Reinforcement n Role of Nucleus Accumbens? l Rada, Mark & Hoebel (1998) n Medial Hypothalamus l stimulation  aversive state l press bar  terminate stimulation n Negative reinforcement l  dopamine in NA l by 100% n Neg RFT blocked by DA antagonist? ~