rofile of executive deficits in cocaine and heroin polysubstance users: common and differential effects on separate executive components.
Verdejo-García A, Pérez-García M.

Department Personalidad, Evaluación y Tratamiento Psicológico, Universidad de Granada, Campus de Cartuja S/N, 18071, Granada, Spain. averdejo@ugr.es

OBJECTIVES: Structure of executive function was examined and we contrasted performance of substance dependent individuals (polysubstance users) and control participants on neuropsychological measures assessing the different executive components obtained. Additionally, we contrasted performance of polysubstance users with preference for cocaine vs heroin and controls to explore possible differential effects of the main substance abused on executive impairment. METHODS: Two groups of participants were recruited: abstinent polysubstance users and controls. Polysubstance users were further subdivided based on their drug of choice (cocaine vs heroin). We administered to all participants a comprehensive protocol of executive measures, including tests of fluency, working memory, reasoning, inhibitory control, flexibility, and decision making. RESULTS: Consistent with previous models, the principal component analysis showed that executive functions are organized into four separate components, three of them previously described: updating, inhibition, and shifting; and a fourth component of decision making. Abstinent polysubstance users had clinically significant impairments on measures assessing these four executive components (with effect sizes ranging from 0.5 to 2.2). Cocaine polysubstance users had more severe impairments than heroin users and controls on measures of inhibition (Stroop) and shifting (go/no go and category test). Greater severity of drug use predicted poorer performance on updating measures. CONCLUSION: Executive functions can be fractionated into four relatively independent components. Chronic drug use is associated with widespread impairment of these four executive components, with cocaine use inducing more severe deficits on inhibition and shifting. These findings show both common and differential effects of two widely used drugs on different executive components.
Cognitive consequences of cannabis use: comparison with abuse of stimulants and heroin with regard to attention, memory and executive functions.

Lundqvist T.

Drug Addiction Treatment Centre, Lund University Hospital, SE-221 85 Lund, Sweden. thomas.lundqvist@med.lu.se

This review aims to compare cognitive consequence between cannabis, and stimulants and heroin with regards to attention, memory and executive functions. The available studies using brain imaging techniques and neuropsychological tests show that acutely, all drugs create a disharmony in the neuropsychological network, causing a decrease of activity in areas responsible for short-term memory and attention, with the possible exception of heroin. Cannabis induces loss of internal control and cognitive impairment, especially of attention and memory, for the duration of intoxication. Heavy cannabis use is associated with reduced function of the attentional/executive system, as exhibited by decreased mental flexibility, increased perserveration, and reduced learning, to shift and/or sustain attention. Recent investigations on amphetamine/methamphetamine have documented deficits in learning, delayed recall, processing speed, and working memory. MDMA users exhibit difficulties in coding information into long-term memory, display impaired verbal learning, are more easily distracted, and are less efficient at focusing attention on complex tasks. The degree of executive impairment increases with the severity of use, and the impairments are relatively lasting over time. Chronic cocaine users display impaired attention, learning, memory, reaction time and cognitive flexibility. Heroin addiction may have a negative effect on impulse control, and selective processing.
Drug Abuse and Addiction

Many people do not understand why individuals become addicted to drugs or how drugs change the brain to foster compulsive drug abuse. They mistakenly view drug abuse and addiction as strictly a social problem and may characterize those who take drugs as morally weak. One very common belief is that drug abusers should be able to just stop taking drugs if they are only willing to change their behavior. What people often underestimate is the complexity of drug addiction—that it is a disease that impacts the brain and because of that, stopping drug abuse is not simply a matter of willpower. Through scientific advances we now know much more about how exactly drugs work in the brain, and we also know that drug addiction can be successfully treated to help people stop abusing drugs and resume their productive lives.

What is drug addiction?

Addiction is a chronic, often relapsing brain disease that causes compulsive drug seeking and use despite harmful consequences to the individual that is addicted and to those around them. Drug addiction is a brain disease because the abuse of drugs leads to changes in the structure and function of the brain. Although it is true that for most people the initial decision to take drugs is voluntary, over time the changes in the brain caused by repeated drug abuse can affect a person's self control and ability to make sound decisions, and at the same time send intense impulses to take drugs.

It is because of these changes in the brain that it is so challenging for a person who is addicted to stop abusing drugs. Fortunately, there are treatments that help people to counteract addiction's powerful disruptive effects and regain control. Research shows that combining addiction treatment medications, if available, with behavioral therapy is the best way to ensure success for most patients. Treatment approaches that are tailored to each patient's drug abuse patterns and any co-occurring medical, psychiatric, and social problems can lead to sustained recovery and a life without drug abuse.

Similar to other chronic, relapsing diseases, such as diabetes, asthma, or heart disease, drug addiction can be managed successfully. And, as with other chronic diseases, it is not uncommon for a person to relapse and begin abusing drugs again. Relapse, however, does not signal failure—rather, it indicates that treatment should be reinstated, adjusted, or that alternate treatment is needed to help the individual regain control and recover.

What happens to your brain when you take drugs?

Drugs are chemicals that tap into the brain's communication system and disrupt the way nerve cells normally send, receive, and process information. There are at least two ways that drugs are able to do this: (1) by imitating the brain's natural chemical messengers, and/or (2) by overstimulating the "reward circuit" of the brain.

Drug Abuse and Addiction

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What happens to your brain when you take drugs? continued...

Some drugs, such as marijuana and heroin, have a similar structure to chemical messengers, called neurotransmitters, which are naturally produced by the brain. Because of this similarity, these drugs are able to "fool" the brain's receptors and activate nerve cells to send abnormal messages.

Other drugs, such as cocaine or methamphetamine, can cause the nerve cells to release abnormally large amounts of natural neurotransmitters, or prevent the normal recycling of these brain chemicals, which is needed to shut off the signal between neurons. This disruption produces a greatly amplified message that ultimately disrupts normal communication patterns.

Nearly all drugs, directly or indirectly, target the brain's reward system by flooding the circuit with dopamine. Dopamine is a neurotransmitter present in regions of the brain that control movement, emotion, motivation, and feelings of pleasure. The overstimulation of this system, which normally responds to natural behaviors that are linked to survival (eating, spending time with loved ones, etc), produces euphoric effects in response to the drugs. This reaction sets in motion a pattern that "teaches" people to repeat the behavior of abusing drugs.

As a person continues to abuse drugs, the brain adapts to the overwhelming surges in dopamine by producing less dopamine or by reducing the number of dopamine receptors in the reward circuit. As a result, dopamine's impact on the reward circuit is lessened, reducing the abuser's ability to enjoy the drugs and the things that previously brought pleasure. This decrease compels those addicted to drugs to keep abusing drugs in order to attempt to bring their dopamine function back to normal. And, they may now require larger amounts of the drug than they first did to achieve the dopamine high—an effect known as tolerance.

Long-term abuse causes changes in other brain chemical systems and circuits as well. Glutamate is a neurotransmitter that influences the reward circuit and the ability to learn. When the optimal concentration of glutamate is altered by drug abuse, the brain attempts to compensate, which can impair cognitive function. Drugs of abuse facilitate nonconscious (conditioned) learning, which leads the user to experience uncontrollable cravings when they see a place or person they associate with the drug experience, even when the drug itself is not available. Brain imaging studies of drug-addicted individuals show changes in areas of the brain that are critical to judgment, decisionmaking, learning and memory, and behavior control. Together, these changes can drive an abuser to seek out and take drugs compulsively despite adverse consequences—in other words, to become addicted to drugs.

Why do some people become addicted, while others do not?

No single factor can predict whether or not a person will become addicted to drugs. Risk for addiction is influenced by a person's biology, social environment, and age or stage of development. The more risk factors an individual has, the greater the chance that taking drugs can lead to addiction. For example:

  • Biology. The genes that people are born with—in combination with environmental influences—account for about half of their addiction vulnerability. Additionally, gender, ethnicity, and the presence of other mental disorders may influence risk for drug abuse and addiction.

  • Environment. A person's environment includes many different influences—from family and friends to socioeconomic status and quality of life in general. Factors such as peer pressure, physical and sexual abuse, stress, and parental involvement can greatly influence the course of drug abuse and addiction in a person's life.

  • Development. Genetic and environmental factors interact with critical developmental stages in a person's life to affect addiction vulnerability, and adolescents experience a double challenge. Although taking drugs at any age can lead to addiction, the earlier that drug use begins, the more likely it is to progress to more serious abuse. And because adolescents' brains are still developing in the areas that govern decisionmaking, judgment, and self-control, they are especially prone to risk-taking behaviors, including trying drugs of abuse.

Prevention is the key

Drug addiction is a preventable disease. Results from NIDA-funded research have shown that prevention programs that involve the family, schools, communities, and the media are effective in reducing drug abuse. Although many events and cultural factors affect drug abuse trends, when youths perceive drug abuse as harmful, they reduce their drug taking. It is necessary, therefore, to help youth and the general public to understand the risks of drug abuse and for teachers, parents, and healthcare professionals to keep sending the message that drug addiction can be prevented if a person never abuses drugs.