The cognitive neuroscience of addiction Flashcards
what is addiction?
Use psychoactive substances reg for variety of reasons
reasons to take alcohol
to relax
sleep
enhance social experiences
reduce anxiety/feelings of depression
coffee
to wake up
nicotine
foe experience
stimulant
social reasons
MDMA
improve social experience
reasons to take cocaine
to be more confident
focus o work
enhance social experience
reasons to take heroin
relax
feel belonging/safety
what % of alcohol users meet criteria for use disorder?
6% - most people don’t get addicted
drug/alcohol/tobacco addicts
experience intense cravings for desired substance and severe withdrawal symptoms when taken away
Can have profound effect on physical and/ mental health
Can have devastating effect on social life and fams
Addicts go to extreme lengths of obtain drug
Depends on how you define it
- Prescription depends on country you’re in
Compatibility with everyday life determining factor
drugs associated with addiction
o Nicotine o Alcohol o Amphetamine o Caffeine o Heroin o Cocaine o (Cannabis) o (Prescription drugs, such as painkillers and Benzo's)
drugs less associated with addiction
o MDMA
o Psychedelics
Muller et al (2011)
- Improved social interaction
- Facilitated sexual behav
- Improved cog perf and counteracting fatigue
- Fac recovery from and coping with psych stress
- Self-medication for mental problems
- Sensory curiosity - expanded perception horizon
- Euphoria, hedonia and high
- Improved physical appearance and attractiveness
cocaine
- Cocaine addiction associated with number of brain damage risks appearing minutes to hours after cocaine consumption, inc stroke in younger adults in early 30’s, seizures, lesions resulting in movement disorders
- More subtle pathology inc reduced volume of inferior portion of frontal lobe
heroin
Associated with broad range of neuropathologies inc reduction in grey matter
brain hypoxia (reduced ox avail)
cerebral oedema (water saturation)
stroke (loss of blood supply)
spongiform leukoencephalopathy (general loss of brain white matter - axons)
myelopathy (paralysis produced by spinal lesions
alcohol
- Strongly linked to Wernicke-Korsakoff syndrome
- Wernicke encephalopathy = general brain shrinkage
- Korsakoff syndrome is chronic ‘end stage’ - psychiatric diagnosis characterised by anterograde amnesia which can be treated with thiamine supplements
- Decreased grey matter
cannabis
- Yücel et al (2008) selected LT heavy cannabis-using men with average of 19.7 years of use with no history of other neuro/mental health complication and contrasted them with 16 control subjects
- Brain volume reduced un users in hippocampus and amygdala
cannabis and psychosis
- Longitudinal research assesses psychiatric status of youth prior to drug use, and then tests again in adulthood
- Odds ration shown for several studies reflect increased risk of diagnosis of psychotic symptoms in indvs who had engaged in heavy cannabis use compared to those who hadn’t
- Odds ratio 1 = groups have equal risk
- Average odds ratio was 2.09, indicating doubling of risk of psychotic symptoms with heavy cannabis use
causes of addiction
- Inter-indv variability in susceptibility to addiction
- 10-20% who use drugs addicted - vary depending on drug
- Similar estimates drawn from research on animal models of addiction - similar % animals systematically administered potent drugs end up preferring them to sucrose
- Genetic contribution to addiction about 50%
Research into the causes of addiction to drugs of abuse has converged on four kinds of causal factors
- Effects of drug-related cues - cue reactivity
- Effects of drug tolerance and withdrawal
- Drugs’ influence of processing of rewards (pleasure and incentives (motivation))
- Drug taking as self-medication in mental illness
a learning perspective
- Associative learning theories of addiction construe drug taking as conditioning
- In instrumental conditioning paradigm the drug is reinforcer which strengthens associations between drug-related cues and drug use
- Becomes predictor
- Cue reactivity
- Form of classical conditioning
- Effect of drug can be seen as US and cues associated with admin seen as CSs
relapse - learning based explanation
- E.g. if stop smoking start process of extinction - reducing the strength of association between cues and smoking
- Take cues out of equation - not extinguished
- Re-exposure to cue elicited conditioned response
- Context-driven relapse extensively documented in rehab
- Extinction procedures that involve exposure to multiple cues w/o reward can be effective, because one reduces potency in triggering relapse
- Research suggests extinction treatments limited to rehab centres less effective than treatments carried out in contexts equiv to those in which addiction developed
- Need to be with cue and not produce behav to fully extinguish the addiction - best way to unlearn behav
we are without defence against the first drink
- Potential of first dose to produce enhanced craving extensively documented and common to most if not all drugs of abuse
- May be that sensory experiences associated with taking the drug are strong cues
- If stopped extinction hasn’t affected cues and on first re-exposure may have elicited strong conditioned response
conditioned compensatory response
- Victims heroin overdose seldom novices - repeated use leads to conditioned compensatory response
- Cases of overdose involve some sig change in context in which drug taken
- Alcohol has stronger effect when consumed as part of exotic drinks and cocktails - change in taste reduces conditioned compensatory response etc
Subkov and Zilov (1937)
o Injected dogs with adrenaline (epinephrine) on several occasions
o Effect of raising blood adrenaline is to increase HR
o Researchers noticed that HR increase following each injection getting smaller
o Dogs developed tolerance to adrenaline
o Organism appeared to compensate for effect of adrenaline by reducing HR around time of injection
o Placed animals in same stand and injected with placebo
o Observed decrease in HR following placebo injection
o Dogs conditioned to reduce HR in response to injection-related context
o Compensatory response didn’t require drug itself - conditioned compensatory response
Siegel et al (1982)
- Injected 3 groups rate with large dose heroin
o First group received previously small dose in exactly same settings
o Second group received small dose in diff cage and room
o Third group heroin-naïve
o Diff between same and diff conditions only explained by effect of
contextual cues
tolerance
- Effects complex
- Form of homeostatic protection to reduce harmful effects of drug
- Can lead to overdose if conditions necessary for it to work absent
- Often results in increase in dose - because larger doses required to achieve desired effect
- Phys mechanisms that underlie tolerance can contribute to withdrawal symptoms
what is the CCR a form of?
tolerance
CCR to alcohol
- Tolerance to alcohol based on desensitisation of GABA receptors where alcohol is agonist
- Has protective role when alcohol consumed, when consumption ceased, it leads to imbalance between excitation and inhibition in the brain, resulting in psych and motor agitation characteristic of alcohol withdrawal
- Pro prevent excess inhibition, organism compensates by reducing sensitivity of GABA receptors in inhib synapses and by increasing activity in excite synapses
what does heroin reduce and tolerance increase?
HR and BP
what happens when heroin is discontinued?
leads to abnormally high BP and HR (as well as insomnia)
what are withdrawal symptoms caused by?
prior adjustments in NS to combat effects of drug when drug no longer there
• Drug pushes something up brain tries to push it down stop drug takes while for brain to stop pushing - brain wants to maintain equilibrium
drugs and rewards
Conditioning models don’t explain relapses later on or why drugs become increasingly desired with use
universal reinforcement circuit
- Studies that employed electrical stim in rates showed that animals prepared to work hard to receive stim of VTA/Nucleus Accumbens
- In humans, PET and fMRI studies shown that presentation of variety of reinforcers causes increased activation in Basal Ganglia in Nucleus Accumbens
- Other research shown in rats, encounters with natural reinforcers leads to dopamine release from VTA neurons in synapses with Nucleus Accumbens
dopamine and reinforcement - Wise et al. (1978)
- Rats trained to press level to obtain food (Wise et al. 1978)
- After training rates split into 3 groups
- For one group level pressing still reinforced by food
- For another lever presses no longer reinforced and gradually animals stopped pressing lever
- Rates in 3rd group given dopamine antagonist pimozide (blocks dopamine receptors) - reinforcement continued
- Animals in 3rd group showed same reduction in lever pressing as those without reinforcement
dopamine - the brain’s pleasure chemical
- Led to anhedonia hyp
- Dopaminergic synapses convey ‘goodness’
- Dopamine antagonists such as pimozide reduce effect, thus reducing animal’s propensity to work for food
dopamine relevance to addiction
- Common findings in addiction is that LT drug users, drug-taking over time results in less euphoria
- Reduction in high
- Craving doesn’t decrease - increases
- Disconnection between ‘liking’ and ‘wanting’
- Some animal studies also provided evidence that dopaminergic synapses primarily processing incentive (motivational) rather than hedonic value of stimuli and that drugs that modulate dopamine influence motivation more than they influence euphoria
dopamine as a work motivator
- 2 groups rate trained to press lever for sugar pellets
- Ione group had dopamine synapses disrupted
- Compared food preferences and lever pressing in 2 groups after training
- Rats from both groups preferred sugar pellets to less tasty food when both avail
- When animals had to press lever, only healthy willing to work for it
what does the incentive salience theory state?
dopaminergic circuit involving NA and VTA not so much responsible for pleasure obtained from drug but for motivation to obtain it
proponents of the incentive salience theory
don’t dispute that euphoria induced by drugs contributes to consumption
claim factors not sufficient to explain addiction in LT users and relapse after therapy
what does the incentive salience theory propose?
addicts become sensitised to drugs as use strongly potentiates motivation-related dopaminergic synapses in brain with repeated use of drug leading to greater responses in dopamine circuit, independently from effects of drug on euphoria
comorbidity
Prob of diagnosis of drug/alcohol dependence increases with severity of mental illness
cause and effect
• Comorbidity between drug dependence and mental illness doesn’t clarify direction of causality
- Drug use could cause mental illness through neurotoxicity
- Mental illness could cause drug dependence through self-medication
- Both causal mechanisms might exist and be reciprocal
experiment induction procedures - McKee et al. (2011)
had Ps describe most stressful event to have occurred to them in last 6 months
• Scripted by clinician, recorded as audio file and later played back to subjects
• In another session received neutral script created in same way
• Then completed ‘abstinence incentive’ task where they could smoke in the next 50m but would earn money for each 5 min period abstinence
• Then smoked ad libitum to determine how much they smoke and how much they enjoy smoking
• Stress decreased delay to initiate smoking in abstinence incentive task
the role of self-medication
- Addicts typically suffer from co-morbidities - disorders
- Often regarded as vulnerability factors/consequences of addiction
- Increasing recognition of fact that addicts may be using drugs to alleviate symptoms of mental illness and this need for ‘self-medication’ may be key factor leading to and/maintaining addiction
what is a primary factor promoting addiction?
avoiding withdrawal
