Mesolimbic Dopamine System and Reward

Question 1

What is ICSS and where is the electrode planted?

Answer 1

ICSS = intracranial self stimulation
acts as a measure of depression
Rodents make a response to obtain electrical stimulation delivered through electrodes (they will work for stimulation)
electrode is implanted in the medial forebrain bundle (MFB)

Question 2

What are the two major dopaminergic areas in the brain?

Answer 2

Nigrostriatal Dopamine Pathway

Mesolimbic Dopamine pathway

Question 3

Nigrostriatal Dopamine Pathway:
- where does the source of dopamine come from?
- Where does the pathway start and end?
- What projections terminate in dorsal striatum?

Answer 3

1. substantia nigra (SNc)
2. SNc –> DS
3. Putamen (dorsolateral striatum) and Caudate (Dorsomedial striatum)

Question 4

Mesolimbic Dopamine Pathway:
- where does the source of dopamine come from?
- Where does the pathway start and end?
- What projections terminate in dorsal striatum?

Answer 4

1. Ventral Tegmental Area (VTA)
2. VTA –> NAC
3. Nucleus Accumbens (NAC) and Olfactory tubercle

Question 5

What is the Mesolimbic Dopamine Pathway known as?

Answer 5

the reward/motivation pathway
regulates motivation, reward value, etc

Question 6

What is Reward Prediction Error (RPE)?

Answer 6

The degree to which one receives more or less reward than is predicted

Question 7

How is RPE coded by dopamine and what are the different expectations?

Answer 7

Reward fully predicted: no change in DA activity, no reward related learning

Reward underpredicted: increased DA response, increased expectation of reward

Reward overpredicted: decreased DA response, decreased expectation of reward

Question 8

What did Schultz et al (1993, 1997) show about RPE?

Answer 8

Schultz measured spiking of dopamine neurons in VTA in awake behaving monkeys
75-80% of midbrain dopamine (DA) neurons displayed short phasic activation or deactivation to different stimulus-events
US = sugar water
CS = tone
learning is driven by changes in the expectations about future salient events such as rewards and punishments

Question 9

What brain region is involved in encoding subjective economic values?

Answer 9

DA neurons in the mesolimbic pathway encode subjective economic value

Question 10

what is liking? How is it measured? What is it mediated by?

Answer 10

Liking = pleasure
hedonic reactions to rewards/outcomes
experienced as an implicit (unconcious) behavior
measured through affective taste reactivity
mediated by opioid system

Question 11

What is wanting? How is it measured? What is it mediated by?

Answer 11

wanting = incentive salience
the process of stimuli gaining motivational value
measured through motivation
food intake and excessive behavior
mediated by dopamine system

Question 12

Can liking and wanting be experienced seperately?

Answer 12

Yes, liking is dissociated from wanting, meaning you can want something but not necessarily like it

Question 13

What is the difference between sign tracking and goal tracking?

Answer 13

Goal tracking: Cs causes conditioned response to where a US is delivered

Sign Tracking
- CS causes conditioned response to the Cs itself (lever)
CS gains incentive salience, it attracts behavior towards itself

***dopamine activity is only necessary for the acquisition and expression of sign tracking, but only for the expression of goal-tracking

Question 14

Naltrexone is an FDA approved opioid antagonist. IF you take some and eat food, what would happen to your orofacial response to food

Answer 14

blocking opioid receptors affects “liking” responses, so this would reduce how much you “like” something

your orofacial reaction would be to smile less when eating this food