Incentive Sensitisation Model

1. INTRODUCTION
1. Most experiment with recreational drugs - vast majority, this does not raise serious concen
2. Small group - casual use leads to compulsive patterns of abuse with detrimental consequences
3. Incentive sensitisation theory offers promising explanation of how drug-induced alterations is psych functions can cause a transition to addiction, and pose major risks for relapse
2. TRANSITION FROM CAUSAL USE TO ADDICTION
1. Changes outlast other changes associated with tolerance and withdrawal
2. Over ast 20 years - increasing recognition that drugs change brain of addicts in complex and persistent ways
3. Important to identify these brain changes and features that make some individuals especially susceptible to transition
3. INCENTIVE SENSITISATION, HYPERSENSITIVITY & BIASES
1. Robinson & Berridge (1993)
2. Most important change is a 'sensitisation' or hypersensitivity to the motivation effects of drugs and drug-associated stimuli
3. Produces attentional processing biases towards such stimuli and pathological motivation for drugs
  1. i.e. compulsive 'wanting' - 'wanting' in quotation marks to refer to activation of incentive salience processes
4. Combined with executive control dysfunction
4. NEURAL SYSTEMS
1. Strong cravings for drugs is controleld by a sensitised neural system
2. System normally functions to link incentive salience to reward cues
3. System consists of mesocorticolimbic dopaminergic neurons that connect to ventral tegmental area with the nucleus accumbens, neostriatum, amygdala, central pallidum, and prefrontal cortex
4. Transforms ordinary stimuli (e.g. cues associated with reward) into incentive stimuli, making them motivationally attractive and able to trigger and urge to obtain reward
5. EFFECT OF DRUGS ON THIS SYSTEM
1. System is highly adaptive under normal conditions - food and sex - ensure survival and procreation
2. System can be sensitised by drugs - taken repeatedly and at high doses, if individual is particularly susceptible
3. System then reacts more powerfully to the drug and related cues
  1. When addict encounters these cues, the urge to take the drug is amplified - creates a vicious cycle as drug abuse and sensitised systems enhance each other - difficult to break cycle
6. 'WANTING' vs. 'LIKING'
1. Ability of a cue to trigger a momentary desire to obtain a reward ('wanting') is independent of the rewarding effect ('liking')
2. 'Wanting' and 'liking' of the drug are linked in the initial phases of drug use, but only 'wanting' becomes sensitised and increases development of addiction
7. 'WANTING' STUDIES & ANIMAL STUDIES
1. Robinson & Berridge (2003) - Drug use amplifies 'wanting' responses, blackade of dopamine has opposite effect
2. Studies using operant running/progressive ratio - animals pre-treated with amphetamine or cocaine are more motivated to work for the drug
8. SELF-REPORTS OF 'WANTING' &HUMAN STUDIES
1. Elevated dopamine levels induced by amphetamine/L-DOPA increase self-reported ratings of 'wanting' but not 'liking' (Liggins et al., 2012)
2. Decreased levels of dopamine diminish self-reported cocaine-induced 'wanting' but not 'liking' (Leyton et al., 2005)
3. Self-reported 'wanting' shown to predict consumption behaviour in at-risk drinkers (Ostafin et al., 2010)
9. DRUG-RELATED CUES
1. Presence of cues predicting drug availability associated with sensitised responding,, while absence is associated with absence of sensitised responding
2. Increased striatal function when salient cues present during teseting subjects at risk of addiction, and drug users, while decreased striatal function when drug-related cues were absent (Casey et al., 2013)
10. BLUNTED RESPONSES TO NATURAL REWARDS & CUES (RELAPSE)
1. Diminished mesocorticolimbic activation to non-addiction rewards/cues obrserved in cocaine abusers, alcoholics, and detoxified alcoholics
2. Also seen in animals exposed to cocaine - prefer cocaine over novelty and even over maternal behaviour and food (Noel et al., 2013)
11. CONCLUSION
1. Addiction involves drug-induced changes in different brain circuits - leads to complex changes in behaviour and psych fucntion
2. Incentive sensitisation combines with defects in cognitive executive functioning - loss of inhibitory control over behaviour with sensitisation of motivational impulses to obtain and drug = potentially disastrous combination

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Incentive Sensitisation Model

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