Cognitive neuroscience of addiction

Question 1

addiction

Answer 1

1. many people use psychoactive substances regularly
2. some people get addicted but most don’t
3. addicts experience intense cravings for the desired substance and severe withdrawal symptoms when it is taken away
4. addicts often go to extreme lengths to obtain the drug

Question 2

what drugs do people get addicted to

Answer 2

1. most common - nicotine, alcohol, caffeine, amphetamine, heroin, cocaine, prescription drugs, cannabis
2. less common - psychedelic, MDMA

Question 3

Neuropathology: cocaine

Answer 3

1. addiction is associated with a number of brain damage risks appearing minutes to hours after cocaine consumption
2. includes strokes, seizures, lesions
3. more subtle pathology includes reduced volume of the inferior portion of the frontal lobe

Question 4

neuropathology: heroin

Answer 4

heroin use is associated with a broad range of neuropathologies including reduction in grey matter, brain hypoxia, cerebral edemia, stroke

Question 5

alcohol

Answer 5

1. alcoholism is strongly linked to the Wernicke-Korsakoff syndrome
2. Wernicke encephalopathy is the general brain shrinkage
3. Korsakoff syndrome is the chronic “end stage”, psychiatric diagnosis characterised by anterograde amnesia

Question 6

Neuropathology: cannabis

Answer 6

1. Yucel et al - carefully selected long term heavy cannabis-using men with an average of 19.7 years of use and contrasted them with 16 control subjects
2. brain volume was reduced in users in the hippocampus and amygdala

Question 7

cannabis and psychosis

Answer 7

1. large scale longitudinal research which assesses the psychiatric status of youth prioir to drug use and then tested again in adulthood
2. odds ratios shown refelct the increased risk of diagnosis of pscyhotic symptoms in individuals who had engaged in heavy cannabis use compared to those who had not
3. results indicate a doubling of the risk of psychotic symptoms given heavy cannabis use

Question 8

causes of addiction

Answer 8

1. a vast amount of research has been carried out into the cause
2. large inter-individual variability in susceptibility to addiction
3. genetic component

Question 9

learning perspective

Answer 9

1. associative learning theories of addiction construe drug taking as conditioning
2. in the instrumental conditioning paradigm, the drug is the reinforcer which strengthens the associations between drug related cues and drug use
3. cue reactivity - clearly detected in brain activity in addicts

Question 10

conditioned compensatory response

Answer 10

1. injected dogs with adrenaline on several occasions
2. the effect of raising blood adrenaline is to increase the heart rate
3. the researchers noticed that the heart rate increase following each injection was getting smaller so dogs appeared to develop tolerance and compensated by reducing their heart rate
4. same response to the placebo injection, so dogs were conditioned to lower their heart rate in response to an injection = conditioned compensatory response

Question 11

leading to overdose

Answer 11

1. heroin tends to suppress activity in the central nervous system, reduces heart rate, respiration rate and blood pressure
2. compensatory response
3. without this response the effect is stronger so more potential for overdose
4. if using heroin in a new environment, the conditioned compensatory response is removed as was relying on context

Question 12

tolerance

Answer 12

1. the conditioned compensatory response is a form of tolerance to the effects of the drug
2. tolerance is a form of homeostatic protection to reduce the potentially harmful effects
3. can lead to overdose and often results in an increase in dose to achieve the desired effect

Question 13

conditioned compensatory response to alcohol

Answer 13

1. tolerance to alcohol is based on the desensitisation of GABA receptors where alcohol is an agonist
2. this has a protective role when alcohol is consumed, when consumption has ceased it leads to imbalance between excitation and inhibition in the brain resulting in psychological and motor agitation characteristic of alcohol withdrawal

Question 14

tolerance and withdrawal

Answer 14

1. heroin reduces heart rate and blood pressure
2. tolerance results in raising blood pressure when using
3. when drug is dicontinued, abnormally high blood pressure and heart rate
4. withdrawal symptoms are caused by the prior adjustments in the nervous system to combat the effects of a drug when the drug is no longer there
   5 . also equals cravings

Question 15

drugs as rewards

Answer 15

1. whilst drug-related cues and avoidance of withdrawal can go someway in explaining the addictive potential of drugs of abuse, they do not seem to capture the whole picture
2. conditioning based models of addiction find it hard to account on their own for the fact that drugs of abuse become increasingly desired with use even with clear negative consequences
3. these limitations of cue reactivity and withdrawal models, along with the discovery of the dopaminergic circuits and their importance for processing of naturally rewarding stimuli, gave rise to the idea that drugs of abuse may be addictive because they’re rewarding

Question 16

universal reinforcement circuit

Answer 16

1. studies that employed electrical stimulation in rats showed that animals are prepared to work hard to receive stimulation of VTA or nucleus accumbens
2. in humans, PET and fMRI studies have shown that presentation of a variety of reinforcers causes increased activation
3. other research has shown that in rats encounters with natural reinforcers leads to dopamine release from VTA neurons in their synapses with nucleus accumbens

Question 17

dopamine and reinforcement

Answer 17

1. rats trained to press lever to obtain food, after training split into three groups
2. one group, lever pressing reinforced by food, other no longer inforced so gradually stopped pressing, third group given dopamine antagonist pimozide, reinforcement continued
3. despite presence of the same reinforcer, animals in third group showed same reduction in lever pressing as those without reinforcement
4. anhedonia hypothesis - dopaminergic synapses convey goodness, dopamine antagnists such as pimozide reduce this effect thus reducing the animal’s propensity to work for food
5. one common finding in addiction is that in long term drug users, drug taking results over time in less and less euphoria
6. some animal studies have also provided evidence that dopaminergic synapses may be primarily processing the incentive rather than the euphoria

Question 18

dopamine as work motivator

Answer 18

1. two groups of rats trained to press a lever for sugar pellets
2. one group had their dopamine synapses in nucleus accumbens disrupted
3. experimenters then compared food preferences between sugar and boring food and lever pressing in the two groups after training
4. rats from both groups preferred the sugar pellets when both were freely available
5. however when the animals had to press the lever only healthy rats would, whereas the rats with the disrupted dopamine transmission would settle for boring

Question 19

incentive salience theory

Answer 19

1. states that dopaminergic circuit involving NA and VTA is not so much responsible for the pleasure obtained from a drug, but not for the motivation to obtain it
2. the proponents of this theory do not dispute that euphoria induced by drugs of abuse contributes to their consumption
3. however they claim that these factors are not sufficient to explain addiction in long term users and relapse after therapy
4. something has gone wrong in our motivation system

Question 20

comorbidity

Answer 20

1. probability of a diagnosis of drug or alcohol dependence increases with the severity of mental illness
2. drug use could cause mental illness through neurotoxicity
3. mental illness could cause drug dependence through self medication
4. both causal mechanisms probably exist and interact

Question 21

possible role of self medication

Answer 21

1. certain drugs can be extra rewarding if someone has a mental health problem
2. increasing recognition of the fact that addicts may be using drugs to alleviate the symptoms of mental illness and that this need for self medication may be a key factor leading to or maintaining addiction