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Lecture 8

Tuesday, Oct 2/2012 - Lecture 8

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Department
Psychology
Course
PSYC 2330
Professor
Francesco Leri
Semester
Fall

Description
Tuesday, October 2 PSYC 2330 Lecture 8 Midterm next Thursday Neurobiology of Prediction Error • Dopamine is a neurotransmitter involved in learning, motivation and a variety of psychobiological functions • Agonists include cocaine, amphetamine, methylphenidate, riddelin • Antagonists include chlorpromazine, haloperidol (anti-psychotic drugs) • Every time there is a problem in prediction (the subject predicts something and it doesn't come true or the subject is not predicting something and something important happens) the organism • The organism learns when there is a discrepency between the organism's previous knowledge and what is occuring currently in the situation ◦ In this case we are discussing the unconditional stimuli • The brain has centers that allow us to detect biologically significant stimuli • Cells that produce dopamine are found in the midbrain ◦ Two clusters ◦ Ventral TegmentalArea ◦ Substantia Nigra ▪ Dopamine from this region is sent to the striatum ▪ The nigra-striatal pathway is damaged in Parkinson's disease ◦ The Meso-[cortico]-limbic dopamine pathway ▪ Transfers dopamine to the limbic system and to the frontal cortex ▪ This pathway is influenced in individuals with schitzophrenia • Antipsychotic drugs block the dopamine receptors so they cannot have as much effect • Dopamine is implicated in schitzophrenia • The result of two much dopamine is psychosis ◦ Hearing voices etc... • Drugs that increase dopamine activity in the brain produce a temporary psychosis resembling positive symptoms of schitzophrenia • Heroin does not reduce dopamine • When dopamine neurons are firing, they are releasing dopamine to their connected areas Wolfram Schultz • Recorded neurons in the Ventral TegmentalArea of monkeys that are awake • US = Drops of juice • UR = Licks • CS's included a variety of visual stimuli • The idea is to pair a single CS with US to create a CR and then record what happens in the brain Dopaminergic Neurons in the VTAencode a Prediction Error • Prior to conditioning, dopaminergic neurons were fired rapidly at the presentation of the US • After conditioning, dopaminergic neurons fire rapidly at the presentation of the CS (in prediction of the presentation of the US) ◦ Between the presentation of the CS and the presentation of the US, the rate of firing does not change • During extinction, dopaminergic neurons fire when the CS is presented, but stop firing completely when no US is presented Pidgeons, Pecking and Food • Auto-shaping • You want to produce a conditioned response – say to peck at a light when the light comes on • Set the computer to turn on the light and then present food • Eventually the animal will peck at the light when it is on even though the pecking does not influence whether or not any food is given • Specific branch of auto-shaping Distinction Between Rats • One group of animals become “sign trackers” • The other group of animals will tend to become “goal trackers” • Some animals, knowing the light is important, will go towards the light first when the light is presented ◦ Go to the sign, then the food • Goal trackers, knowing the food is coming, will go towards the food when the light is presented ◦ Skip going to the sign, go directly to the food • Does that mean that the same system is acting differently in different rats? Microdialysis • Allows us to sample the fluid in the brain • Sampled from the nucleus accumbens within the ventral tegmental area ◦ Nucleus accumbens is the meeting place of the limbic and motor systems (Allows motivated movement) • Measures the amount of dopamine in the brain fluid • Done on rats that were selectively bred to be sign trackers or goal trackers Results of Microdialysis • Measures the amount of dopamine release compared from baseline • In the sign trackers ◦ In the initial stage of conditioning, there is a little response to both the CS and the US ◦ The response to the CS gets bigger and bigger as conditioning continues ◦ The response to the US gets smaller and smaller as conditioning continues ◦ Sign trackers attribute more and more value to the CS as compared to the US (Making the connection between the CS and the US) • In the goal trackers ◦ Never de
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