W9L1 - Dopamine Flashcards
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 does dopamine synthesize
Tyrosine > Dopamine > Dopamine > Noradrenaline
What is tyrosine
Amino acid found in food
What is between tyrosine > dopa
Tyrosine hydroxylase
- Synthesize Enzyme
What is between Dopa > Dopamine
Amino Acid Decarboxylase
- Synthesize Enzyme
What is between Dopamine > 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
What is methylphenidate (ritalin)
Treatment of ADHD
Blocks reuptake of DA and noreadrenaline
How do addictive drugs work with reward response
- Addictive drugs hijack reward response
- Codes reward better than expected due to DA release (everytime)
- Quicker release = More Addictive
What did animal models of addiction showed
Animals will repeatedly press the buttom to release drugs until they die.
Drugs and Free Will Problem
- Drugs initiate “wanting” and in addicted people, this leads to drug urges or cravings.
- Impaired cognitive control/PFC caused by excessive dopamine
- Cognitive control + Craving = Addiction
Does quicker DA release = addictive?
Not always.
Might be more important in behaviour and cognitive control [craving] rather than euphoric feeling. (Some addictive drugs slower DA but more addictive)
Euphoric = Opioid system
Is there individual suspectability in addiction?
More individual differences in susceptibility compared to drug addiction.
Addiction exists to more things (can be real, symbolic, or virtual) more than drugs.
