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Flashcards in week 9-dopamine Deck (17):
1

dopamine pathways

-Substantial Nigra (SN)
Motor Control
-Ventral Tegmental Area (VTA)
Motivation & emotional response
Reward, desire & addiction

2

Dopamine Synthesis

-Tryrosine
an amino acid
found in food
(Tryrosine Hydroxylase
SYNTHESIS
ENZYME)
-DOPA
-Dopamine
-Noradrenaline
(norepinephrine)
( look at lecture slide)

3

dopamine synthesis-l-dopa

L-DOPA
(Amino Acid decarboxylase
SYNTHESIS
ENZYME)
dopDopamine β-hydroxylase
SYNTHESIS
&
BREAKDOWN
ENZYME
amine)
noradrenaline

4

Dopamine & Parkinson’s

-Caused by death of dopamine cells in the Substantia Nigra
-Disease initially characterized by motor tremor. Later symptoms include cognitive impairments and dementia. Symptoms often includes reduced “executive function”.
-There is currently NO CURE of the disease, but symptoms can be reduced through drugs and deep brain stimulation.
-Treatment of the disease can cause impulsivity, hypersexuality, gambling, addictive like behaviours (see section on Reward & DA).

5

Dopamine & Parkinson’s
continued

-Areas of the brain such as the basal ganglia are believed to help inhibit/control motor action.
-In the healthy brain DA release allows selective activation of the basal ganglia & initiation of motor commands.
-In Parkinson’s the lack of DA makes it hard to initiate complex motor actions & control small corrective movements. > patients shake when trying to stay still & have trouble initiating movements like standing, walking, reaching etc

6

Reward Prediction Error

If an unexpected reward occurs DA neurons become more active and release a burst of DA
-Originally thought every time something good happens there must be dopamine in the brain but it is more dedicate than that,
Each horizontal row bit of a neuron
Burst of dopamine firing

7

Reward Prediction Error 2

-If a reward is repeatedly given after a stimulus (such as a beep) then the reward will be “expected” & no DA will be released with the reward but will now be released at the time of the beep
-If you keep doing that you get the burst of activity at the beep instead of at the reward
Codes expectation
If you get money and I want to buy shoes, you get excited when you get the money, especially if unexpected

8

Reward prediction error 3

If a reward is “expected” & not provided DA neurons will be suppressed

9

Reward - Real & Virtual

Rewards can be
- real (e.g. food or sex)
- symbolic (e.g. money)
- virtual (e.g. points in a game)
DA is involved in all cases.

10

Drug Addiction

-A chronic relapsing disorder which consists of a compulsive pattern of drug-seeking and drug-taking behaviour
-takes place at the expense of other activities
-persists despite adverse consequences

11

DA Drugs - Cocaine

Reuptake of transmitter (BLOCKED)

12

DA Drugs - Amphetamine

Drugs = ice (most pure) and speed (less pure)

Reverses uptake transporter actively expelling DA and NA out of the neuron which also prevents DA uptake
Reuptake of transmitter (REVERSED)

13

Addictive drugs hijack reward response

-Addictive dopamine drugs are ALWAYS coded by the brain as “Better than expected
-compared to normal condition of: When reward is expected NO additional dopamine is released

14

Addiction & Dopamine

-Reward is coded by the brain if there is increase DA in the Nucleus accumbens (Nac) and other forebrain structures like the amygdala, hippocampus, prefrontal cortex (Pfc).
- Addictive drugs produce extra dopamine release in the Nac (sometimes via different pathways)
-The more DA released the greater the high
-The faster the DA release the more addictive it will be

15

Addiction and free-will

-1st problem
Drugs initiate “wanting” and in addicted people, this leads to drug urges or cravings.
-2st problem
Cognitive (“top down”) control is reduced by impaired function of the prefrontal cortex (PFC) caused by excessive dopamine.
-imaging studies show PFC abnormalities
-Final Result – addictive behaviour
Failures of “top down” control would contribute to loss of control over the urge to take drugs.

16

Addiction beyond drugs

Cases of “addiction” exist for most things that are rewarding
- real (e.g. food or sex)
- symbolic (e.g. money/gambling)
- virtual (e.g. gaming
-More individual differences in susceptibility compared to drug addiction

17

lecture summary

-Dopamine is synthesised by the brain from amino acids in food or from drugs containing L-DOPA
-Dopamine is important in Parkinson’s disease & Addiction
-Dopamine codes reward “relative to expectations”-
Addictive drugs that cause the release of DA are always coded by the brain as “Better than expected.” They also reduce the ability for the prefrontal cortex to provide “top-down” control of behaviour.