DA and Reward Value

substantial nigra (SN)

produces dopamine for motor control - Midbrain structure part of basal ganglia

• nigrostriatal system - neurons in SN project to neostriatum (part of basal ganglia) incld the caudate nucleus and putamen

• connected to frontal cortex

ventral tegmental area (VTA)

produces dopamine. Involved in motivation and emotional response, reward, desire and addiction

• mesolimbic - projects DA to several parts of limbic system incl amygdala, hippocampus and nucleus accumbens - nucleus is important in reward effects of certain stimuli incl drugs

• mesocortical - project DA to prefrontal cortex - excitatory effect on prefrontal cognitive processes incl short term memory formation and planning

dopamine

neuromodulator that plays a key role in reward, motivation, and motor control.

dopamine synthesis

• starts as tyrosine - amino acid found in food e.g. nuts, cheeese

• tyrosine hydroxykase turns it into L-DOPA

• amino acid decarboxylase transforms into dopamine

• dopamines decactivated into noradrenaline by dopamine B-hydroxylase

monoamines

contains only 1 amino group. Dopamine, norepinephrine, and serotonin

L-DOPA

inmmediate precursor of dopamine - both natural and synthetic drugs for Parkinson’s

Parkinson’s disease

Degeneration of dopaminergic neurons connected to caudate nucleus in substantia nigra = reduction in dopamine = motor tremor with later symptoms including congitive impairments and dementia

• reduced exectutive function

• no cure currently - but symptoms can be reduced through drugs and deep brain stimulation

why is L-DOPA used to treat Parkisons

L-DOPA is an intermediate of dopamine but unlike DA it can cross the blood-brian barrier and thus be used in drugs to up-regulate dopamine synthesis

• synthetic L-DOPA is identical to natural

problems with Parkinson’s symptom treatment

can cause impulsivity, hypersexuality, addictive like behaviours

reward prediction error study

monkeys in cages - used single electrode in brain to measure action potentials. during the experiment they were given juice as a reward

• graph with histrogram showing average action potentials

• peak in histrogram = dopaminergic firing action potentials when given juice

• next stage - gave beep before reward given = after many trials cells fired when beep and no additional dopaminergic changes when given juice = dopamine more related to expectation of reward?

• then beep and no reward = suppression of activity

reward prediction error

difference between expected and received rewards informs learning and decision-making processes

• brain predicts whether outcome will be pos/neg and dopamine is involved in altering the brain whether the prediction was correct or there was an error (more/less than expected)

reward

• real - food or coitus

• symbolic - money - just paper yet holds value in people’s eyes

• virtual e.g. points in game

reward related cue learning

process by which cues associated with a reward become predictive of that reward, enhancing learning and motivation.

value-modulated attentional capture task

measures propensity to learn reward-related cues even at expence of adaptive functioning/goals

• identify target in diamond and determine whether horizontal or vertical line

• 80% of time also includes distractor - 1 is a high valule distractor, 1 low value

• when high value distractor = if identify target quickly you get bonus points

• people with propensity to addiction distracted by high value queue at the detriment of their performance

congitive effort

the mental resources required to perform a task or solve a problem, often influenced by the perceived value of rewards.

• feeling of cog effort seems linked to working memory and cognitive control

• DA codes both goal reward and effort costs = aversive feeling of cog effort reflects opportunity cost

opportunity costs

the potential benefits an individual misses out on when choosing one option over another

episodic future thinking

the ability to project oneself into the future and imagine specific events or scenarios - relies on working memory

• poor EFT = difficulties appreciaring and applying knowledge of benefits of delaying gratification - more likely to choose instant grat/not engage with persistent, long-term gradual reward tasks

how can EFT be improved

practices like visualization, goal setting, and engaging in mindfulness exercises = enhance ability to imagine future scenarios

• possible treatment for alcohol dependency

gambling and DA

upredictability adds to boost of DA

• if you predictably lost 70% of money = not addictive

• if unexpected large wins while still losing avergae 70% = wins coded as positive = addicted

drug addiction

chronic relapsing disorder with consist compulsive pattern of drug-seeking and drug-taking behaviour

• at expense of other activities

• persists despite adverse consequences

DA and cocaine

dopamingeric drug = blocks reuptake of dopamine into presynpatic = increase DA levels in synapse = affects neural signalling

• positive experiences feel more rewarding than expected when high = increases use

DA and amphetmines

ice and speed - blocks reuptake of DA and reverses the transporter releasing more DA

• turns tasks not initially rewarding into rewarding = even more rewarding than expected

• long term brain changes with dependence due to overstimulating dopaminergic cells leads to permanent changes and cell death

methylphendiate

Ritalin - treatment for ADHD. dopamine and noradrenaline reuptake inhibitor

effect of drugs on reward responses

• normal - when reward is expected after beep/cue = no DA reward response

• drugs - cue/trigger = dopaminergic activity for cue and always DA reward response when takes drugs

• drugs always coded by brain as better than expected = 2 peaks in DA activity

why is ritalin not seen as addictive to its similar addictive counterparts (speed/coke)

Ritalin - slower and more controlled increase in dopamine levels = reduces potential for instant gratification and subsequent addictive behaviors.

animal models of addiction

rodents put in box with 2 cues (light and olfactory) and 2 buttons 1 is inactive and other is drug-paired

• kept pressing drug-paired till it died even over food

addiction and DA

drugs cause increased DA signalling

• more DA released = greater high

• faster DA release = more addictive

addiction v freewill

1. drugs initiate wanting causing people with addictions to get cravings (bottom-up)

2. cogntive (top-down) control reduced bc of impaired prefrontal cortex functioning due to excessive DA

3. failures of top-down = loss of control over the urge to take drugs