Hockenbury Discovering Psychology 5th txtbk

166 CHAPTER 4 Consciousness and Its VariationsFOCUS ON NEUROSCIENCEThe Addicted Brain: Diminishing RewardsAddictive drugs include alcohol, cocaine, heroin, nicotine, and theamphetamines. Although their effects are diverse, these addictivedrugs share one thing in common: They all activate dopamineproducingneurons in the brain’s reward system (Li & others, 2007;Volkow & others, 2009). The initial dopamine surge in response toan addictive drug is a powerful brain reward, one that prompts theperson to repeat the drug-taking behavior (Self, 2005).The brain’s reward system evolved to reinforce behaviors thatpromote survival, such as eating and sexuality. A wide range ofpleasurable activities can cause a temporary increase in dopa minelevels, including exercising, listening to music, eating a deliciousdessert, and even looking at an attractive person.But in contrast to such naturally rewarding activities and substances,addictive drugs hijack the brain’s reward system. Initially,the drug produces the intense dopamine-induced feelings ofeuphoria. But with repeated drug use, the brain’s reward pathwaysadapt to the high dopamine levels. One result is that the availabilityof dopamine receptors is down-regulated or greatly reduced(Volkow & others, 2007). Along with decreased dopamine activity,other biochemical changes dampen or inhibit the brain’s reward circuits,reducing the pleasurable effects of the abused substance.These adaptations create the conditions for drug tolerance—moreof the substance is now needed to produce a response that is similarto the drug's original effect (Nestler & Malenka, 2004).As the brain’s reward circuits down-regulate to counter thedopamine surge, another change occurs. The normally reinforcingexperiences of everyday life are no longer satisfying or pleasurable.Emotionally, the addict experiences depression, boredom, andapathy (Little & others, 2003).While lying in a PET scanner and viewing images of a beautifulsunset, laughing children, or other pleasurable scenes, thecocaine addict’s brain shows little or no dopamine response.But when shown even brief flashes of images associated withcocaine use—a coke spoon, a syringe, the neighborhood wherethe drugs were bought—the brain's reward circuit “lights up likea Christmas tree” (Hoffman & Froemke, 2007). Thus, becauseeveryday experiences are no longer enjoyable, the addict is evenmore motivated to seek out the reinforcing effects of the drug.At this point, the addicted person needs the substance not toget high but just to feel “normal.”When the addictive drug is not taken, withdrawal symptomsoccur, accompanied by intense craving for the abused substance.What causes the craving? One explanation is that the neurons inthe brain’s reward circuits have become hypersensitive to theabused substance. Because the neurons physically change, thissensitization can be long-lasting, persisting for months and evenyears after drug use has ended. This is also why relapse canoccur long after someone has stopped abusing drugs. SimplyComparisonSubjectCocaineMethamphetamineAlcoholDrugAbuserCommon Effects of Abused Drugs Different abused drugs initiallyproduce their intoxicating effects in the same way—by increasingdopamine levels in the brain’s reward system (Volkow & others,2009). But as the brain adjusts to the effects of drug abuse, longtermchanges occur in the brain’s reward circuitry. In the brainscans shown here, orange and yellow areas indicate the greatestnumber of dopamine receptors. As you compare the scans, you cansee that regardless of the specific drug, drug abuse sharply reducesthe number of dopamine receptors in the brain’s reward system.being exposed to drug-related stimuli or stressful life events cantrigger craving—and relapse (Volkow & others, 2006).With advanced imaging techniques, researchers are pinpointingthe structural and functional changes in the brain’s reward systemin response to drug abuse (Fowler & others, 2007). By identifyingthe common biochemical and physical changes that occur, scientistsmay one day be able to create more effective treatments tocounteract the destructive effects of addictive drugs.drug abuseRecurrent drug use that results in disruptionsin academic, social, or occupational function -ing or in legal or psychological problems.depressantsA category of psychoactive drugs thatdepress or inhibit brain activity.In contrast to drug use, drug abuse refers to recurrent drug use that results inthe disruption of academic, social, or occupational functioning or in legal or psychologicalproblems (American Psychiatric Association, 2000a). In the UnitedStates, rather than illicit drugs, alcohol is, by far, the most widely abused substance(Substance Abuse and Mental Health Services Administration, 2009).