Saturday, February 6, 2010

Of Love,Darwin,Addiction and Emotions

artbox by marguerita and The Evolution of Happiness

Q: What is your current thinking regarding the neural mechanisms underlying this flattened sensitivity to non-drug rewards?

A: Individuals with lesions to certain regions of their PFC, including the OFC, have difficulties in modifying behavior appropriately in response to altered reinforcement situations in their environment. Similarly, drug-addicted individuals also have PFC structural changes (e.g., reduced volumes), OFC and ACC functional changes (e.g., increased response when craving), and parallel behavioral changes (e.g., increased impulsivity). These findings led us to ask what role the OFC and ACC play in the drug-addicted individual’s ability to modify behavior based on the salience and value of a given reinforcer.

We think that drug addiction may be better understood as a disorder of neural regulation. Here’s why: even though the OFC and ACC are not sufficiently engaged in the processing of non-drug-related rewards, they are activated—in addicted individuals but not controls—in response to drug-related cues (e.g., words/pictures/videos of drug taking or pharmacologically similar drugs). Indeed, our preliminary fMRI results suggest that a possible communication breakdown between PFC sub-regions (OFC and dorsolateral PFC) may underlie the disrupted perception of motivational drive and the impaired control of behavior that characterized the drug-addicted individuals in our study.

Q: What does this work suggest in terms of clinical implications for treating drug addiction?

A: Consistent with the compulsive and chronically relapsing nature of drug addiction, our findings may help explain why efforts to control addiction through reinforcement can be compromised. It is possible that instead, efforts should be focused on devising new training and skill-development strategies and on supervised pharmacological interventions, all with the goal of decreasing the reinforcing effects of the drug, enhancing the relative value attributed to non-drug-related rewards, and increasing control of behavior.

Together, these approaches may enhance the ability to control drug-taking behavior even in situations when the desire for the drug exceeds that for other rewards.

Among the different approaches for diagnosis, prevention, and treatment of drug addiction, exploring the evolutionary basis of addiction would provide us with better understanding since evolution, personality, behavior and drug abuse are tightly interlinked. It is our duty as scientists to explore the evolutionary basis and origins of drug addiction so as to uncover the underlying causes rather than continuing to solely focus on the physiological signs and global activity of this epidemic. Too often the treatment of addiction simply works to alleviate the symptoms of addiction, dealing with overcoming the physiological dependence and working through withdrawal symptoms as the body readjusts to a non-dependent state of homeostasis. However, we must not only concentrate on this aspect of addiction when considering global treatments and preventative programs. We must take into consideration that it is not purely the physiology of addiction we are battling.

Drug addiction is thought of as an adjunctive behavior, or a subordinate behavior catalyzed by deeper, more significant psychological and biological stimuli. It is not just a pharmacological reaction to a chemical but a mode of compensation for a decrease in Darwinian fitness . There are three main components involved in substance addiction: developmental attachment, pharmacological mechanism, and social phylogeny including social inequality, dominance, and social dependence . Developmental attachment created by environmental influences, such as parental care or lack thereof, may influence children's vulnerability to drug addiction. Evolutionarily speaking, children that receive care that is more erratic may focus more so on short-term risks that may have proved to be an adaptive quality for survival in ancient environments. Compounding that attachment, the pharmacological mechanism describes the concept of biological adaptation of the mesolimbic dopamine system to endogenous substance intake. These factors combined with the influence of social phylogeny create a position for predisposition to drug addiction. They attribute to the common belief that many substances of abuse have great powers to heal, and that is often the driving motivation for overuse and addiction. Evolutionary perspective shows an intermediate and fleeting expected gain associated with drug addiction correlated with the conservation in most mammals of archaic neural circuitry , most often being a falsified sense of increased fitness and viability related to the three components of drug abuse [5,8]. The chemical changes associated with fitness and viability are perceived by mammals as emotions, driving human behavior.
Human behavior is mediated primarily by dopaminergic and serotonergic systems, both of ancient origins probably evolving before the phylogenetic splits of vertebrates and invertebrates . 5-HT (serotonin), stimulated by a small range of drugs, mediates arousal. It is believed to be inhibited by hallucinogens and also helps control wanting for ethanol and cocaine consumption. The cortico-mesolimbic dopaminergic system, on the other hand, is believed to be the target of a wide range of drugs, including marijuana and cocaine, increasing the transmission of dopamine to the nucleus accumbens . This system mediates emotion and controls reinforcement, and is the primary pathway acted on by antipsychotic drugs such as chlorprothixene and thioridazine. Problematic use of drugs develops into addiction as the brain becomes dependent on the chemical neural homeostatic circuitry altered by the drug [7]. No matter the theory of drug addiction, there remains one constant: withdrawal is inevitable. As a drug is administered continuously and an individual becomes addicted, the brain becomes dependent on the presence of the drug. With an absence of the drug, withdrawal symptoms are experienced as the brain attempts to deal with the chemical changes. There are believed to be evolutionary origins of drug addiction, which will be discussed further, as well as a link between physiological addiction and the evolution of emotion.

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