What are the 2 areas releasing and synthesizing dopamine?
- ) Substantial Nigra (SN)
- ) Ventral Tegmental Area (VTA)
Can neuromodulators be released from the same neruon?
No, But they can interact with one another at another brain region
What does SN and VTA do?
SN:
- Motor Control
VTA:
- Motivation and Emotional responses
- Reward and addiction
Where does SN and VTA send to?
- Amygdala
- Nucleus Accumbens (NAc)
- PFC
- Straitum
How is dopamine synthesized?
Tyrosine > Dopamine > Dopamine > Noradrenaline
What is tyrosine?
Amino acid found in food
What is between the conversion of tyrosine to dopa?
Tyrosine hydroxylase
- Synthesize Enzyme
What is between the conversion of Dopa of Dopamine?
Amino Acid Decarboxylase
- Synthesize Enzyme
What is between the conversion of Dopamine to Noradrenaline?
Dopamine β-hydroxylase
- Synthesize and breaks down dopamine
What is the drug to help dopamine?
L-Dopa instead of Dopa
Synthesis further on remains the same (Amino Acid Dehydroxylase > Dopamine > Dopamine-P-Hydroxalse > NA)
What causes PD?
Death of dopamine in substantial nigra
What are symptoms of PD?
Initial:
- Motor tremor
Later
- Cognitive and EF impairments like dementia
What is the cure for PD? What is the problem?
No cure, but symptoms can be reduced by
- Drugs
- Deep brain stimulation
- However, treatment may cause impuslivity, gambling, etc…
What does “reward” represent?
- Real
- e.g. food or sex
- Symbolic
- e.g. money
- Virtual
- e.g. points in a game
Reward Prediction Error: What happens when an unexpected reward is presented? Why?
DA burst
Gain or loss is unexpected the feelings associated are often more intense.
Reward Prediction Error: What happens when an expected reward is presented?
No da burst on reward on set, DA burst on beep onset
Reward Prediction Error: What happens when expected reward but not given?
Suppressed da burst on reward on set, DA burst on beep on set (as usual)
What does DA code?
Outcomes relative to expectations.
Reward and Effort Cost.
- Aversive feeling of cognitive effort reflects “opportunity cost”
- Coding for absense of reward.
What are effort costs?
Every other rewarding thing one could be doing
When will effort task persistence endure or disengage?
Endure
- When the incentive of goals outweighs the cost
Disengage
- When the incentive of cost (opportunity cost) outweighs the goals
Incentives can help with motivation because they counterbalance opportunity cost.
Why is gambling addictive?
Unpredictability adds to boost of DA (‘better than expected’)
- Predictably losing 70% every bet would not be addictive
- Unexpected large wins (but still losing an average of 70%), the wins are coded as extremely positive
What is drug addiction?
A chronic relapsing disorder involving compulsive drug-taking and drug-taking at
- expense of other activities; AND
- despite adverse consequences
What does cocaine do biochemcially?
Blocks reuptake of dopamine
What is ice and speed? What happens biochemically?
Ice: more pure
speed: less pure
Not only blocks, but reverse uptake transporter actively expelling DA and NA out of the neuron
