David J. Linden

David J. Linden

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Adı:
David J. Linden
Unvan:
Profesör, Yazar
In humans, rats, and other mammals, the reward circuits is much more complex, as it is interwoven with brain centers involved in decision-making, planning, emotion, and memory storage. When we find an experience pleasurable, it sets in motion several processes with different time courses: (a) We like the experience (the immediate sensation of pleasure); (b) we associate both external seonsory cues (sights, sounds, odors, etc.) and internal cues (our own thoughts and feelings at the time) with the experience, and these associations allow us to predict how we should behave to repeat it; and (c) we assign a value to the pleasurable experience (from a little to a lot), so that in the future we can choose among several pleasurable experiences and determine how much effort we are willing to expend and risk we are willing to take in order to get them.
What makes pleasure so compelling is that, through the interconnection of the pleasure circuit with other brain regions, we adorn it with memory, with associations and emotions and social meaning, with sights, sounds, and smells.
Whatever our prejudices, the truth is, given the right circumstances (which can include factors like high stress, early drug exposure or childhood abuse, poor social support, or genetic predisposition), anyone can become a drug addict. Addiction is not just a disease of weak-willed losers. Indeed, many of our most important historical figures have been drug addicts — not only the creative, arty types like Charles Baudelaire (hashish and opium) and Aldous Huxley (alcohol, mescaline, LSD), but also scientists like Sigmund Freud (cocaine) and hard-charging military leaders and heads of state from Alexander the Great (a massive alcoholic) to Prince Otto von Bismarck (who typically drank two bottles of wine with lunch and topped it off with a little morphine in the evening).
Social psychologists who have interviewed people in long-term relationships find that the intense, initial phase of romantic love typically lasts from nine months to two years, to be replaced, in most couples, by a less intense form of loving companionship. Given what we know about the distortions of thought and self-image and the sexual obsession that accompany the early phase of love, one has to wonder about our laws. Most states in the United States require a six-to twienty-four-month delay before granting a divorce, but anyonce can get married immediately. One could make a case that to promote good, long-term marriages, the delay should be mandated on the front end.

A small number of people do report that their feelings for their partner are just as intense ten or twenty years on as they were soon after they first met. Most of these individuals seem to be telling the truth abou the depth of their emotions. When Brown's research group performed the lover's-face brain imaging experiment on subjects whose love relationship had lasted for ten years or more, they found an interesting result. Most of the long-term lovers no longer showed strong activation of the VTA dopamine center—the other brain changes were mostly intact, but the pleasure circuit no longer got that cocaine-like jolt. However, in the small group that still reported being intensely in love, the VTA pleasure circuit remained strongly activated by the image of the lover's face. That interesting result validates the idea that a minority of couples can indeed keep that glow of new love burning beyond the initial infatuated state of a relationship. However, the ultimate causality here is not clear.
Opium, prepared from the poppy plant, Papaver somniferum, was in use long before the time of imperial Rome. Evidence from the archeological record places it in Mesopotamia (present-day Iraq) around 3000 BC. Opium was widely consumed—either by being eaten, dissolved in wine, or inserted in the rectum— for both medical and ritual purposes by the ancient Egyptians and by the Greeks soon thereafter. The Ebers Papyrus, an ancient Egyptian medical text from the year 1552 BC, even recommends opium as an aid to help small children sleep. One method to achieve this was to smear the drug on the nipples of the nursing mother.
Why is cigarette smoking so addictive when its psychoactive effect is comparatively so subtle? The reason is that the cigarette is the Galil assault rifle of the nicotine delivery world: fast and reliable. Consider that while a heroin user injects a hit and feels a potent ephoric rush about fifteen seconds later, he is not going to inject again for many hours. The cigarette smoker, on the other hand, will typically take ten puffs from a single cigarette and will often smoke many cigarettes in the course of a day. Each puff will deliver nicotine to the pleasure circuit about fifteen seconds later, approximately the same delay as for intravenous heroin. So while a typical heroin addict may get two strong, rapidly delivered hits per day, the pack-a-day cigarette smoker will get two hundred weak, rapidly delivered hits per day. But why does the nearly instant delivery of a drug to the brain, as with smoking cigarettes or injecting heroin, carry a higher risk of addiction than slow delivery of the same drug, say, by chewing tobacco or eating opium?

One way to think about this is to consider that addiction is a form of learning. When someone uses a drug, associations are made between a particular act (injecting the drug or chewing the tobacco) and the pleasure that follows. Imagine that you have a dog that you're trying to train to come when called, using a tasty morsel of food as a reward. If you want to create a learned association, you'll call the dog, and when it comes you'll immediately give it the treat. Now imagine that instead of presenting the reward immediately (as with injected heroin), you wait thirty minutes and then offer the reward (as with ingested opium). In the latter case, the connection between the behavior (coming when called) and the reward is quite weak, and the association is less likely to be learned. The same dog-training anaolgy holds true for injected heroin (one big pleasure rush) and cigarette smoking (many tiny pleasure rushes). If you call the dog once a day, and then immediately reward its compliance with a ten-ounce steak, it will eventually learn to come when called. If you call the dog twenty times per day and immediately reward each correct behavior with a small chunk of meat, the dog will learn much more quickly. So when we smoke cigarettes, we are being very effective trainers of our inner dog, creating a strong association between puffing and pleasure.
As addiction develops and tolerance, dependence, and cravings emerge, the euphoria produced by the drug gradually drains away. Pleasure is replaced by desire; liking becomes wanting. In everyday speech, we may say of an alcoholic, "She really loves to drink," or of a cocaine addict, "He must love to get high." We imagine that drug addicts experience more pleasure from their drug of choice than others and that this motivates their complusive drug-seeking. However, most active addicts report that they no longer derive much pleasure from their drug of choice. Accumulating evidence indicates that once the trajectory of addiction is under way, pleasure is suppressed, and it is wanting that comes to the fore. Unfortunately, pleasure in the drug itself isn't the only sensation diminished in addicts, for addiction produces a broad change in the pleasure circuit that also affects the enjoyment of other experiences, like sex, food, and exercise.
Most of our cultural influences (and the diet industry) insist that overeating and obesity result from a failure of willpower. However, the evidence from genetics argues strongly against that idea: Data from adoptions and twin and family lineage studies indicates that about 80 percent of the variation in body weight is determined by genes. That's about the same degree of heritability as a charateristic like height, and much greater than that for other conditions that we now clearly regard as running in families, including breast cancer, schizophrenia, and heart disease.
Perhaps the hardest thing about imagining the distant future of pleasure is not the technology involved, but rather the social, legal and financial systems that will surround it. When anyone can precisely control his or her pleasure circuits with an inexpensive head-mounted noninvasive device, how will this ability be used, abused, commercialized, and regulated? If our past experience with psychoactive drugs is any indication, it will be an unholy mess. At various points in our recent past, alcohol, nicotine, heroin, and cocaine have all been legal, banned, taxed, and regulated by the government. Our drug policies reflect a complex web of competing interests.
Tobacco is highly addictive, and smoking it kills millions every year, yet it is mostly tolerated. It's almost impossible to kill yourself with cannabis, yet it remains criminalized.
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Adı:
David J. Linden
Unvan:
Profesör, Yazar

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