The Addicted Brain Read Online Free Page A

2009.)

    When offered one of almost any of the drugs that humans abuse (exceptions being those that distort sensations and perceptions, such as hallucinogens like LSD), the animal almost always chooses the lever that results in drug delivery. The sensation brought about by the infusion of the drug is positive and acts as a
reward
that positively
reinforces
the act of pressing the lever. Every lever press, followed by an infusion of the sensation-producing drug, further reinforces the lever-pressing behavior. The animal appears hooked, pressing the lever repeatedly. In the case of a rewarding drug, such as cocaine, the animal might ignore food, water, or even a sexually available mate, and it presses the lever until it is too exhausted to continue. Although the animal controls the act of lever pressing, the researcher controls the total amount of drug that is administered and prevents the animal from taking enough to injure or kill itself accidentally, as sadly can happen with humans.
    If the researcher suddenly reverses the levers so that the one delivering cocaine now delivers saline, the animal soon discovers the drug-related lever and starts pressing it. If the drug is removed completely, the animal keeps lever pressing for some time, apparently in the hope that it will reappear. It might require a large number of unsuccessful presses to “extinguish” the pressing behavior, meaning the animal no longer associates pressing the lever with the desirable sensation and stops.
    In these controlled experiments described previously, the animals have access to a restricted amount of drug over a restricted time. But the human situation doesn’t always work that way. Sometimes drug users have access to a drug for a long, extended time. George Koob, his colleagues, and others 3 studied this in animals. They allowed some animals to have longer access to the drug. For example, rats were allowed to self-administer cocaine for either one hour or six hours per day. In the group with one hour access, cocaine intake was lower and stable over days. But the group that had six hours of access gradually
increased
its intake over days. Access and availability of a drug canmake a difference in the amount of drug that is taken. This is consistent with the behavior of heavy drug users.
    Because the drug self-administration paradigm has been so successful, it is a trusted model for human addiction. It is used to determine if new drugs or medications are potentially addicting. For example, if some compound X affects the brain, it is reasonable to see if it is self-administered. If it is, then it has to be considered as a potentially dangerous and addicting substance.
    Because of the robust self-administration of drugs in both animals and humans, there seems no other explanation than the fact that animals and humans share some property in the brain that makes the sensation produced by these drugs desirable. In other words, there seems to be some hardwiring in the brain that is shared by both humans and animals that facilitates drug addiction. The danger of addiction is a biological vulnerability that both humans and animals share. Some see this as evidence that widespread drug-using behavior in humans cannot be simply explained as a moral weakness because a biological basis for it exists.
Darwin Saw It
    Looking back, it shouldn’t be surprising that at least some animals share an interest in drugs with humans. In 1871, Darwin made some interesting observations that are humorous and enlightening.
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    On Booze, Men, and Monkeys
    “Many kinds of monkeys have a strong taste for tea, coffee, and spirituous liquors: They will also, as I have myself seen, smoke tobacco with pleasure. Brehm asserts that the natives of north-eastern Africa catch the wild baboons by exposing vessels with strong beer, by which they are made drunk. He has seen some of these animals, which he kept in confinement in this state, and he gives a laughable account of their