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6 Cards in this Set
- Front
- Back
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identify importance of ‘reinforcement’, & outline discovery of brain stimulation reward
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motivation - ‘hedonism’, ‘drive reduction’
learning (conditioning) - ‘law of effect’ mental illness - ‘anhedonia’ drug abuse - ‘dependence’ (+ve & -ve reinforcement) yet, nothing known about physiological basis until mid-1950s James Olds & Peter Milner (1954) using electrical stimulation of brain to study functions of midbrain reticular formation poor surgical accuracy in one subject led to discovery of ‘pleasure centres’ in the brain phenomenon known as brain stimulation reward or intracranial self-stimulation ICSS ICSS combines electrical brain stimulation with lever-pressing in Skinner box - ‘DIY’ once established, ICSS is very stable phenomenon observed in many species goldfish, pigeon, rat, goat, dolphin, monkeys & humans in humans, stimulation of same brain areas produces feelings of intense pleasure - likened to orgasm Early objections to ‘reward’ interpretation of ICSS in rats?a forced motor loop? perhaps stimulation elicits rapid movement of paws = bar-p |
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detail the catecholamine hypothesis & review early evidence for key role of dopamine
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German & Bowden 1974
ICSS reward is strongly associated with the major catecholamine pathways probability of ICSS mesolimbic dopamine system = 78-100% nigrostriatal dopamine system = 50-100% dorsal noradrenaline system = 40-100% outside these 3 systems = 8% [highest probability in MFB - why?] Correlation vs causality correlation insufficient to prove causal link how to test hypothesis? - pharmacology early data supportive increase in NA/DA increased ICSS decrease in NA/DA decreased ICSS typical drugs involved? [although non-selective for NA vs DA, NA assumed to be the reward transmitter - ‘in vogue’ during 60s] Tyrosine-->Dopa-->Dopamine-->Noradrenaline (step blocked by disulfiram Noradrenaline or dopamine? Roll (1970) - disulfiram (ICSS) Kelly (1974) - disulfiram, phentolamine & spiroperidol (ICSS, locomotion & rearing) but Rolls et al (1975) - spiroperidol (motor complexity issue) key problem - performance vs reward? (analogy with feeding research) N.B. phentolamine = NA receptor blocker |
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explain the problem of performance vs reward
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By 1978, lots of evidence consistent with involvement of dopamine in reward processes - but nagging doubts remained about problem of performance vs reward
Wise (1978) ‘one of the main problems with the cateholamine (dopamine) hypothesis of reward is not so much with the hypothesis but with the technique used to study it’ |
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review other lines of evidence supporting a role for dopamine in a common brain reward system
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Although ICSS remains a useful research tool, at least 4 other methodologies have been delevoped to study role of dopamine in reward processes
behavioural contrast drug self-administration conditioned place preference brain microdialysis BEHAVIOURAL CONTRAST: Origin - Crespi (1942) in rats trained to lever-press for food reward:- a sudden decrease in objective reward magnitude disproportionate fall in response rate (negative contrast) a sudden increase in objective reward magnitude disproportionate elevation in response rate (positive contrast) dopamine mediates reward, should be possible to detect a shift in the subjective value of reward without altering its objective value used saccharin (high vs low) as reward tests with haloperidol (dopamine antagonist) & apomorphine (dopamine agonist) results as predicted haloperidol - negative contrast apomorphine - positive contrast |
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show relevance of this system to drug abuse
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DRUG SELF-ADMINISTRATION:
humans, pleasurable effects of drugs play major role in development of dependence in the laboratory, animals readily learn to self-administer certain drugs subjects fitted with i.v. catheter or i.c.v. cannula; bar-pressing leads to drug infusion one of most avidly self-administered groups of drugs are the psychostimulants e.g. amphetamine, cocaine & nicotine Analogous set-up to ICSS but lever pressing delivers drug rather than electrical stimulation Dopamine synthesis inhibitors/receptor blockers reduce euphoric effects of amphetamine & cocaine in humans [Jonsson et al 1971; Gunne et al 1972] Dopamine receptor antagonists (e.g. pimozide) increase responding for amphetamine & cocaine in rats - as if attempting to overcome ‘blocked’ reward [Yokel & Wise 1976; Roberts et al 1977] Destruction of dopamine terminals in the nucleus accumbens reduces self-administration of nicotine in rats [Corrigall et al 1992] Genetic deletion of the dopamine transporter dramatically reduces |
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attempt to reconcile evidence that dopamine is involved in aversive as well as appetitive motivation
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