10. Neurophysiology of Reward and Addiction Flashcards

1
Q

Define motivation

A

process that mediates goal-directed responses or coal-seeking behaviour to changes in the external or internal environment

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2
Q

Define Saliency

A

something important in the surrounding environment worth paying attention to

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3
Q

Define reinforcement

A

consequence of operant behaviours that alters the probability that a behaviour will be repeated under similar conditions each time

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4
Q

Define Reward

A

objects, stimuli or actiivities that have positive valie

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5
Q

Define aversion

A

a negative reinformement of behaviour that the individual will learn to avoid future encounters

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6
Q

Define pleasure

A

a positive sensation often referred to as euphoria or hedonia

promotes survival of self and others

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7
Q

Describe how dopamine and drug use go together? (longest FC ever)

A
  • dopaminergic neurons encode the discrepancy between reward predictions and info about the actual reward received and send this signal to the reward learning centers of the brain
  • unpredicted reward elicits an activation (positive prediction error; a happy suprise)
  • a fully predicted reward elicits no response (exactly what you thought would happen)
  • Omission of a predicted reward induces a depression (sad that you didn’t get what you thought you would)
  • events that always precede reward assigns value to the reward itself
  • with repeated drug use, repetition of these reward prediction error signals reinforces drug related cues and behaviours
  • natural rewards (not drug related) produce error-correcting DA-RPE signals only until the predictions match reality
  • as a result, when given a choice between drugs or natural reward, there is a bias towarsd the drug that strenghtens with each use
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8
Q

Drugs reinforce drug use via dopamine. How so?

A

drugs can increase extracellular dopamine concentrations in the limbic region and nucleus accumbens and last longer and are in larger amounts than other natural reinforcers like food and sex

cocaine, meth, and ecstasy increase dopamine directly by inhibiting dopamine reuptake or promoting dopamine release

ETOH, nicotine, opiates and MJ work indirectly to increase dopamine levels

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9
Q

What causes a drug abuser to seek out more drugs, especially in certain environments?

A

Salience allows certain enviromental sensory cues associated with the drug can increase dopamine levels and elicit the desire for more drug

Salience also contributes to drug induced dopamine increases leading to the procurement of more drug

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10
Q

What keeps us from feeling pleasure all the time ?

A

GABAnergic neurons release GABA from the nucleus accumbens to the prefrontal cortex

this inhibits pleasure

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11
Q

How do we overcome the inhibition by the Nucleus Accumbens to feel pleasure based on pleasurable stimuli?

AKA dopamine-hypothesis of reward

A

when a reward is elicited, the ventral tegmental area becomes activated to inhibit the nucleus accumbens in five steps

  1. dopaminergic neurons from the VTA project to the NA
  2. DA is released into the NA
  3. DA inhibits neurons in the NA
  4. NA activity decreases
  5. decreased NA activity allows for pleasure to be sensed
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12
Q

What type of rewards activate the ventral tegmental area?

A

Excitatory amino acids (prefrontal cortex)

orexin (hypothalamus after eating)

Ach (dorsal tegemental area)

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13
Q

How is the ventral tegmental area inhibited to stop the pleasure sensation?

A

GABAnergic neurons from the nucleus accubnes release GABA back onto the ventral tegemtnal area

also releases dynorphin as a co-transmitter which binds to kappa-opiod receptors and supresses further dopamine release from the VTA

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14
Q

What is the dopamine-independent reward pathway?

A

the ventral tegmental area can aslo be activated by opioids (endogenous via exercise, ethanol, etc)

Via activation of mu receptirs, they activate dompinaergic neurons in the VTA, activate local interneurons in the NA, and activate the PFC causing pleasure/euphoria

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15
Q

What are some major outcomes of chronic drug exposure in the brain?

A

it alters the morphology of neurons in the dopamine regulated circuit

it can alter the expression of transcriotion factors and prorteins

it can change the level of NTMs in the brain, leading to more compulsive and disinhibited behaviour

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16
Q

What is the role of CREB in physical dependency on a drug?

A

physical depednency is due to excessive noradrenergic output from the locus ceruleus and CREB dependent upregulation of target genes in the locus ceruleus

17
Q

What is the role of deltaFosB and AP-1 in dependency?

A

these are upregulated by stress and drug abuse

upregulates expression of: AMPA/NMDA, elements of cell signal transduction pathways and factors promoting drug seeking, motivation and locomotion

this occurs over months to years and causes structural changes

18
Q

Saliency of substances in the nonaddicted brain

A

the saliency of substances (non-addicted) and substnaces cues should be low in the non-addictive brain because the brain inhibits the drive to seek such substances

conditioned cues have little or no influence on the saliency of drug-substances

the saliency of natural rewards greatly overrides the saliency of drugs

19
Q

Saliency of substances in the addicted brain

A

The saliency of substances (addicted to) and substance related cues is increased.

this overrides the PFC control of behaviour and can now no longer inhibit the drive to seek substances

conditioned cues reinforce the saliency of substances, further increasing the substance seeking behavior

the saliency of the substances overrides the saliency of natural rewards, which no longer influence behavior