Bio 337 Lecture 18: Brain Behavior Reward

What is a reward

A subjective feeling of pleasure or discomfort associated with certain experiences

Why do we have rewards

To preserve itself and helps us choose wisely

Palatable

food that taste good

Palatable food taste types

Sweet, salty, and Umami (amino acids)

Aversive foods

Foods that don’t taste good

Aversive food taste types

Bitter and Sour

How to measure reward without relying on subjective evaluations?

Through observation and quantification of objective behvaiors

Three different ways to measure reward

1. Measuring consumption (preference)

2. Measuring motivation (wanting)

3. Measuring Hedonic Value (Oro-facial reactions)

Measuring reward through consumption

1. Can be measured through the consumption of a solution in a one bottle test as volume of the solution consumed or the number of licks.

2. Can measure consumption of different solutions to see consumption rates to see which solutions deliver the most reward. (licking diff concentrations of NaCl)

3. Measuring preference of one solution over another in a two bottle test.

Two-bottle test

Test that tests for preference for one reward over another through measuring consumption rate between two different solutions

Measuring reward through motivation

1. Can quantify motivation through how much an animal is willing to work to receive that reward.

2. Progressive Ratio scheduling

   1. How many lever pulls is the breaking point for diff sucrose concentrations. More lever pulls equals more motivation.

3. Go/No-Go Task

   1. Sound plays and rat will decide if it should pull the lever or not. If sound plays for sucrose then the rat will pull the lever fast but avoid it for quinine cue.

Measuring reward through hedonic value

1. Observing the amount of facial reactions to measure the palatability of a reward. Palatable foods result in tongue protrusions and aversive stimuli results in tongue gapes.

Plasticity of rewards

The reward value of a solutions isn’t fixed and can depend on experience. It is conditioned taste aversion.

AKA Something can be conditioned to become unpleasant or pleasant

How can wanting be measured

Desirability
By looking at autoshaping/consumption

How is liking measured

Pleasantness

By looking at oro-facial reactions

Does wanting and liking rely on the same parts of the reward system?

NO. Wanting can occur without liking and vise versa.

How to find the neural circuit involved in processing reward? (finding reward areas)

1. Recording neural responses

2. Self stimulation

3. Lesion studies (manipulations of brain activity)

Finding the neural circuit involved in processing reward? Recordings

Measure neural responses to reward stimuli in specific areas/regions in the brain.

Finding the neural circuit involved in processing reward? Self Stimulation

Induce self stimulation utilizing levers and electrodes where the electrode is in a specific part of the brain. If it stimulates a reward center, the mouse will keep pulling the lever.

EXAMPLE: VTA

Finding the neural circuit involved in processing reward?
Lesions

In humans: neurological studies (stroke, tumors, calcifications
In animals: Targeted inactivation/lesion and/ or pharma

Lesion studies of Kluver and Bucy

Demonstrated the role of the amygdala in emotions and reward

Kluver-Bucy Syndrime

Lesion found in the Amygdala

Symptoms:
Agnosia, oral behaviors, eating disturbs, hyperactivity, hypersexuality, reduced emotional reaction

Parts of Limbic System

1. Cingulate Cortex, Prefrontal Cortex, Insular cortex

2. Hypothalamus

3. Ventral part of basal gnaglia (nucleus accumbens and globus pallidus)

4. Mediodorsal Thalamus

5. Amygdala

6. Ventral Tegmental Area (VTA)

What does the Limbic system control?

The brain’s reward system

Limbic functional circuit

1. Reward related inputs from amygdala, orbito/medial prefrontal and ventral hippocampus are sent to the nucleus accumbens.

2. Accumbens receive dopaminergic inputs from the VTA

3. Dopamine increases responsiveness of accumben neurons

4. Leads to increased inhibition of pallidum

5. Leads to decreased inhibition of mediodorsal thalamus

6. Excitation to cortex which receive DA inputs.

Cue development for dopaminergic neurons in VTA

If cue anticipated reward, dopaminergic neurons fire at the cue instead of after the stimulus. If no reward occurs than the DA neurons stop firing.

What does dopamine mediate

Dopamine mediates wanting

Tongue protrusions

Liking a solution while gapes means not liking.

Opioids mediate what?

The hedonic value of rewards

Where are hedonic hotspots located?

In the accumbens and the ventral pallidum

How does injection of mu-opioids affect wanting and liking

Can either enhance or reduce liking as well as enhance wanting.