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Lecture 24

PSYCH 110 Lecture 24: LECTURE #24_ REWARD AND ADDICTION (04_13)

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Robin Ball

LECTURE 24: REWARD AND ADDICTION (0413) Dopaminergic neurons in VTA send signals to NAc Most drugs increased signaling in the dopamine neurotransmitter system Different drugs produce different withdrawal symptoms and severity Withdrawal symptoms lead to physical dependence on the drug Substantia nigra (part of basal ganglia, located in the midbrain) is one place in the brain where dopaminergic neurons are located Substantia nigra sends input into basal ganglia in striatum which is controlling movement (remember parkinson disease) Ventral tegmental area (VTA) (neurons in midbrain) is making lots of different connections, important one is with the nucleus accumbens (NAc) this is the reward pathway, if you stimulate these neurons, gives the person feelings of pleasure Dopamine is being released from the VTA onto NAc VTA also making synapses on prefrontal cortex (motivation and planning) and amygdala Intracranial selfstimulation Rat can press a lever that will stimulate its own brain In most areas in the brain, the rat doesnt really care, but if you stick the electrode into VTA or NAc, the rat will keep pressing the lever (wont mate, eat food, drink water overriding natural rewards) addictive, keeps pressing until falls over to sleep If give dopamine antagonist, the rat will press the lever less natural stimulus activating sensory areas in the brain then send signals to prefrontal cortex and limbic system and then both of those will activate the VTA Dopamine also goes to amygdala and prefrontal cortex (red lines from VTA to PFC and limbic system) NAc has output to different areas of brain involved in motivation and changing behavior (hypothalamus, prefrontal cortex, etc.), these behaviors help animal realize that they should do the behavior more to keep obtaining the stimulus VTA neurons respond to reward prediction error Recordings from VTA, some neurons are responding to predicting a reward Done in monkeys, electrode in neuron in VTA 1 Monkey given juice, natural (unexpected) reward responding to reward 2 trained monkey that before given juice, see a flash of light, classical conditioning, VTA neuron is active before given the juice, when given juice (expected reward), not much change in APs 3 flash the light, but dont get the reward, neuron is almost silent for the time when the reward was supposed to be given How to test how reward a drug is in rats Experiment 1 Rat is administering the drug to itself through a lever Look at how many times the rat presses the lever to see how addictive the drug is Experiment 2 Rat given a drug in polka dot room vs. a diamond room
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