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Positive Reinforcement,
Craving, and Choice - Coggle Diagram
Positive Reinforcement,
Craving, and Choice
Drug Self-
Administration
- behavioural economic theories regard the decision to take drugs as similar to the decision to obtain any luxury item > determined by the expected reward size against costs.
- withdrawal and tolerance theories dominated thinking from the 60s to 80s, but from then on, positive reinforcement theories became a more broadly accepted view.
- defence of the notion that drugs gave rise to addiction through their rewarding effects came from self-administration procedures.
rats
- electrical self-stimulation experiments: rats readily acquire instrumental responses to obtain brain stimulation.
- administration of drugs increases sensitivity to the rewarding effects of stimulation, suggesting a common biological substrate.
- responding for stimulation is pathological
- drugs establish similar pathological SA behaviour in some individuals.
- pathological > the behaviour can continue for long periods of time (binge episodes), it will displace the pursuit of other rewards (like food), and is maintained despite the behaviour incurring severe harm.
- was found that all rats would typically acquire self-administration behaviours, however, this procedure doesn't model the typical human drug user, who chooses between the drug and other alternatives > lacks some validity.
- rats readily acquire drug SA, suggesting this is initially established by the positive reinforcing effects of drugs.
- drug SA similar to instrumental responses acquired to obtain other appetitive rewards (eg food)
- drugs appear to be like other natural rewards in reinforcing behaviours that lead to their procurement.
Choice
- choice-procedure: rats have access to two levers, one of which produces the drug, whilst the other produces an alternative reward.
- ahmed (2012): preference for cocaine over saccharin.
- 20% developed cocaine preference whereas remainder preferred saccharin.
- more consistent with data on the prevalence of drug dependence in humans (~20%).
- choice procedures indicate the more drug-dependant an individual is, the more value they ascribe to their drug of abuse, over an alternative.
matching law (1970):
- choices are allocated between two options in accordance with the relative frequency of rewards earned by those choices.
- the allocation of behaviour by animals across two options conforms with the matching law, when the same rewards are used between the two options.
bias:
- when there are different rewards available, bias can influence choice.
- baum (1974): when a preferred reward is produced by one response, a bias (K) can add a constant proportion of responding to the favoured alternative.
demand curve
- represent the amount of a particular reward that consumers will purchase/consume at a given price.
- if the drug price is low, more of it will be consumed. as price increases, consumption decreases, until the 'breakpoint' at which users will cease consumption.
- most economic decision theories assume:
- the value of each reward
- the probability of the response producing that reward.
- the costs associated with the reward.
- these values are combined to calculate the utility of each possible action.
- drug dependence may be driven by the drug being considered as having a higher reward value, which endows this reward with higher utility, and thus drug administration increases in frequency as a proportion of total behaviour.
Behavioural
Sensitisation
- observed when the locomotor response to a drug is augmented following chronic use.
- park et al (2010): cocaine pre-treated group showed a greater distance travelled in response to the cocaine injection compared to the saline pre-treated group.
- not residual, persists for long periods after last dose.
- 'reverse tolerance' because if tolerance had occurred the locomotor effect should have been reduced.
- not due to a build-up of the drug over repeated dosing, because a sensitised response to a test dose has been shown to persist for years since administration.
- not due to tolerance, because you'd see a reduced locomotor response following chronic exposure.
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