Somatic Marker Hypothesis - Drug Addiction

Drug Addiction

Despite being aware of the medical, social and legal problems associated with consuming illegal substances, substance dependent individuals (SDI) incessantly take part in activities that ultimately lead to addiction and dependency. This myopia for the future is characteristic of drug abusers and can be applied to somatic markers. The Somatic Marker Hypothesis attributes SDI difficulty in making advantageous decisions to a defect in an emotional mechanism, which indicates the future consequences of an action and helps select the best response. This emotional mechanism is a special feeling that emerges in bioregulatory processes, and can be produced in the body or in brain areas. When a negative somatic marker (like fear) is juxtaposed to a particular future outcome, it functions like a warning, signaling us to refrain from an action. Positive somatic markers act as an added incentive to behave in a particular way. Through this process, somatic markers help control human tendency to discount the future since long term costs associated with a negative somatic marker have the potential to deter an individual away from making a decision.

According to the SMH, there should be a connection between abnormalities in expressing emotions and experiencing feelings, and severe impairments in decision-making. Much of the evidence for this comes from the Iowa Gambling Task (IGT), which provides testing of human decision processes in regard to immediate rewards and delayed punishments, risks, and uncertainty of outcomes. The results from the IGT studies support the notion that impaired decision-making in substance dependent individuals is associated with varying reactions to rewarding and punishing events. For example, it was apparent which packs of cards had the greatest risk for loss, but individuals continued to choose from the high-risk, high-reward packs. Thus the prospect of immediate high reward clearly outweighed the negative long term consequences for SDI. Damasio (1994) suggests that somatic markers provide a covert, non-conscious estimate of which cards are good and bad based on the rewards and punishments received. Prior to any conscious cognitive process of selection, initial sorting occurs and then the individual is guided in a theory about the gambling game more efficiently. Somatic markers, put more simply, appear to be a fast mechanism for reasoning that allows individuals to make satisfactory decisions without the necessary time to go through a lengthy analysis. They are advantageous, and thus adaptive.

One of the more frequently used models, the International Affective Picture System (IAPS), consists of a large set of images categorized according to their normative values in three dimensions: valence, arousal, and control. Using this model, Gerra et al. (2003) analyzed the neuroendocrine responses of both substance dependent individuals and healthy individuals in order to induce pleasant and unpleasant emotions. The results showed that in response to unpleasant images, SDI showed decreased activity in several neuroendocrine markers, including norepinephrine, cortisol, and adrenocorticotropic hormone levels. SDI showed a more level response pattern to both pleasant and unpleasant images, suggesting that they may have a diminished emotional response to natural reinforcers other than drugs.

Consistent with this evidence, a neuroimaging study conducted on drug craving by Garavan et al. (2000) demonstrates that drug related stimuli have the ability to activate brain regions involved in emotional evaluation and reward processing. This study exposed two groups, one including experienced cocaine users (N=17) and the other including non-users (N=14), to three separate films: individuals smoking crack cocaine, outdoor nature scenes, and explicit sexual content. Meanwhile, all patients underwent functional magnetic resonance imaging, which monitored thirteen regions of the brain. Three regions of the brain, the anterior cingulated, right inferior parietal lobule, and the caudate/lateral dorsal nucleus, displayed significantly greater activation during the cocaine film than during the sex film in the cocaine users, suggesting that cocaine cues activate similar parts of the brain as natural stimuli in cocaine users. Additionally, cocaine users exhibited a lower response than the non-users to the sex film, suggesting that drug-users demonstrate a lower emotional response to natural reinforcers other than drugs. Although the somatic states linked with natural reinforcers may not be strong enough to influence decisions in substance dependent individuals, these studies demonstrate how strong somatic states associated with drug abuse have the potential to dominate decisions regarding drug use. Modern day drugs like cocaine were not popular throughout human evolution, and so it seems obvious that natural responses are affected by habitual cocaine use.