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Which brain regions control reinforcement?
- Frontal cortex
- Nucleus accumbens
- Striatum
- Substantia nigra
- Hippocampus
- Ventral tegmental area
- These areas control the salience of the reward, pleasure from reward, motor functioning, compulsion, and preservation of the conditioned response
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Label this
- 1: Caudate nucleus
- 2: Putamen
- 3: Striatum
- 4: Basal ganglia
- 5: Globus pallidus
- 6: Lateral medial
- 7: Subthalmic nucleus
- 8: Substantia nigra
- 9: Thalmus
- 10: Deep cerebellar nuclei
- 11: Cerebellum
- 12: Pons
- 13: Spinal cord
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What is this? Also label it
- The midbrain dopamine system
- 1: Prefrontal cortex
- 2: Striatum
- 3: Nucleus Accumbens
- 4: Septum
- 5: Limbic cortex
- 6: Substantia nigra
- 7: Olfactory tubercle
- 8: Amygdala
- 9: Ventral tegmental area
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How have rats contributed to our understanding of the reinforcement system?
- rat in chamber with electrode in brain. In chamber rat can scurry around and can press lever.
- Once rat discovers lever causes stimulation, the rat will press it more and more (Olds & Milner)
- If electrode is in the dorsal palms, VTA, lateral hypothalamus, the rat will continue to press lever
- All these regions are connected as they lie in the medial forebrain bundle: set of axons from Ventral Tegmental Area.
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What other things cause a reward response in the brain?
- Food increases dopamine response
- As does sex
- Cigarettes and cannabis cause a rise in the dopamine levels of the nucleus accumbens
- Cocaine and amphetamine cause a rise in nucleus accumbens dopamine
- If dopamine is blocked, rats self administer it more, try harder to get the effects
- Lesions to the nucleus accumbens decreases how much they self administer with the lever
- Injection of opiates causes a rise in Nuc. Acumbens dopamine.However, lesions to the Nuc. Accumbens do not impair opiate self-administration. Therefore, there must be a separate pathway.
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How is reward response measured?
Use a micro-dialysis implanted in the brain to measure hormone levels
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Why does heroin make you feel good?
Thought to increase the release of GABA, which leads to an increase in dopamine levels in the nucleus accumbens
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How does the mesolimbic brain reward circuitry work?
- Enkaphalin (an opioid) is released
- This binds to an opiate receptor, which inhibits the system that inhibits GABA release
- More GABA is released, and this causes more dopamine to be released
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Which neurotransmitters are involved in the effects of the major drugs, and which brain regions do they act on?
- Cocaine and amphetamines: Dopamine & serotonin, Nucleus accumbens and amygdala
- Opiates: Dopamine & opioid peptides (probably), ventral tegmental area and nucleus accumbens
- Nicotine: Dopamine & opioid peptides (probably, Nucleus accumbens and amygdala (probably)
- THC: Dopamine & opioid peptides, VTA
- Ethanol: Dopamine, opioid peptides, serotonin, GABA, Glutamate, VTA, nucleus accumbens and amygdala
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What are the main counterarguments to the dopamine theory of pleasure?
- Schizophrenics are not “fat and happy”
- Addicts often continue drug-taking even when they do not feel pleasure.
- Dopamine surges in Nuc. Accumbens not only after pleasurable but also after unexpected or painful events
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What is 'liking'?
The subjective feeling of niceness. In animals it refers to hedonic reactions such as lip-licking to a sweet substance
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What is 'wanting'?
- Having the desire to obtain something.
- Note that it is dissociable from liking. An addict may want a cigarette but not actually like smoking it!
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What is 'learning'?
- After experience, a subject develops associations, representations and predictions based on past experiences.
- E.g. After many hangovers one may eventually learn to modify their hedonic reactions to alcohol
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What are the neurological differences between liking and wanting?
- Opioid receptors in Nacc have different effects and hotspots for liking and wanting separately
- The main region thought to be involved in liking is the orbital frontal cortex, which codes for valence or 'liking' (and pleasantness of water in a thirst experiment)
- Even higher-order rewards such as monetary reward were found to correlate with activity in the medial OFC (O’Doherty et al. 2001)
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What does the striatum do during conditioning?
- Sometime activation happens when observing CUE for reward (that has been learnt), so have something to do with predicting reward.
- In trials where cue is shown, and then no reward came, the neurons turn off and become silent.
- 'Prediction error' is the magnitude of prediction area can be quantified.
- 45 humans, delayed discounting task (similar to marshmallow expt)
- More activity in Nacc, the greater the desire of the immediate reward rather than delayed reward.
- Inhibiting in Nacc are more likely to delay gratification.
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