impulse control Flashcards
the birth of psychosurgery
- Antonio Egas Moniz
- “Some, you would not suspect that there was anything especially
wrong with them. They may have seemed a little shallow, but you
might not even be struck by that. There were people who went back
to work and held responsible jobs after lobotomies, and others who
essentially became vegetables. Some became very impulsive and
childish in their behaviour. The operations were so crude. Different
parts of the brain were damaged, and the outcomes varied widely.” - Professor Elliot Valenstein
- “Some, you would not suspect that there was anything especially
- Introduction of antipsychotic Thorazine by GSK marked end of lobotomies as treatment for mental illness.
function of the frontal cortex
- “When there is a choice between something harder and something easier, and the harder thing is the better thing to do,…(the frontal cortex) is the thing that makes you do the harder thing.”
- Robert Sapolsky
Iowa gambling task
- Subjects choose from 4 “decks” of cards
- Total of 100 choices from decks
- Two decks large short-term gain, long-term loss (non advantageous)
- Two decks smaller short-term gain, long-term gain (advantageous)
- Subjects were patients who had sustained unilateral focal damage to the frontal lobes and healthy controls.
- Frontal lesion subjects show impaired decision making compared to control subjects, and persist with disadvantageous decks, in spit of obvious failure.
- Clark et al, Neuropsychologia, 2003
main substance of abuse
- Alcohol - ethyl alcohol/ethanol
- Nicotine
- Heroin, morphine, codeine, and other opioid agonists
- Cocaine, cathinone, amphetamine, and other psychostimulants
- THC
- Sedatives - e.g., Barbiturates, Benzodiazepines, methaqualone and analogues
- Hallucinogens:
- Psychedelics - e.g., LSD, DMT, ibogaine, mescaline, psilocybin, salvinorin A
- Dissociatives - e.g., PCP, ketamine, methoxetamine, dextromethorphan
- Deliriants - e.g., atropine, scopolamine, hyosyamine
- Inhalants - e.g., hydrocarbones contained in gasoline, kerosene, and natural gas, toluene, 3-ethyltoluene, xylene, acetone, amyl nitrite, nitrous oxide, trichloroethane, trichloroethylene, chloroform
why do some people take some drugs
· Experimentation - novelty seeking; exploration
· Pleasure - drugs as desired rewards (liking/desire)
· Medication - to relieve unpleasant states (anxiety, depression, pain)
· Peer pressure - to be cool
- These reasons describe much (most) drug taking
what is not addiction
· Experimental use
· Recreational (casual) use
· Circumstantial use
- But taking drugs doesn’t equal addiction
addiction
· From the latin word ‘addictus’ meaning ‘bound’ or devoted to
· Three characteristics:
1. Compulsive drug seeking and taking
2. Inability to stop and high rates of relapse after cessation
3. Why drugs become more wanted and less liked
* Although many try drugs, dew become addicted (individual differences)
* 60% try/use illicit drugs, 90% if we include legal drugs (e.g., alcohol), but only 5-10% develop and addiction
- E.g., of cocaine users, only 15-16% develop a cocaine addiction within 10 years of their drugs use (Lopez-Quintero et al, 2012)
Diagnostic statistical manual, 5th edition (DSM-5) diagnostic criteria for substance use disorders:
- A problematic pattern of substance use, leading to clinically significant impairment or distress, as manifested by at least two of the following, occurring within a 12-month period:
- The substance is often taken in larger amounts or over a longer period than was intended.
- There is a persistent desire or unsuccessful efforts to cut down or control substance use
- A great deal of time is spent in activities necessary to obtain the substance, use the substance […]
- Craving, or a strong desire or urge to use substance
- Recurrent substance use resulting in a failure to fulfil major role obligations […]
- Continued substance use despite having […] social or interpersonal problems […]
- Important […] activities are given up or reduced because of substance use
- Recurrent substance use in situations in which it is physically hazardous
- Substance use is continued despite […] physical or psychological problems […]
- Tolerance […]
- Withdrawal […]
* Mild - presence of 2-3 symptoms
* Moderate - presence of 4-5 symptoms
- Severe - presence of 6 or more symptoms
frontal function in drug users
- PET scan of glucose metabolism in control brains and cocaine abusers.
- Reduced OFC function in cocaine users compared to control subjects during protracted withdrawal.
- Volkow et al, 2001
Bechara et al, 2001 - Neuropsychologia:
- Like subjects with frontal lesions, substance. Dependent subjects show impaired decision making (persistence with disadvantageous deck on Iowa sorting task), in spite of obvious failure.
Delay discounting in Methamphetamine-dependent subjects:
- Subjects asked to choose which option they would or wouldn’t want.
- Meth users more quickly choose the smaller-immediate reward.
- Hoffman et al, psychopharm 2006
why not just experiment using humans
- Largely because of more severe ethical limitations, especially when dealing with drug-naive subjects
- Problem of casualty
drugs change your brain
- Amphetamine self-administration produced structural changes (dendritic spines) lasting > 1 month, in limbic forebrain regions of rats.
- So, long-term drug use may lead to increased impulsive behaviour/loss inhibitory control due to changes in prefrontal cortex
- But the relationship may also exist in the opposite direction:
Individual differences in ‘trait’ impulsivity may be a risk factor to drug taking
summary
- Prefrontal cortex involved in impulsive decision making, including temporal discounting;
- Drugs produce long-lasting changes in brain areas involved in motivation, emotion and decision making/inhibitory control;
- These brain changes result in behavioural changes, including increases in impulsive decision making;
- Pre-existing (‘trait’) differences in impulsivity may contribute to increased risk to take drugs.
