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  • Hungry Dogs

    SCIENCE NEWS
    August 22, 2003

    Hungry Humans React Like Pavlov's Dogs


    Most people would probably consider their tastes more discerning than those of the family pet. But according to new research, humans can be trained to crave food in a manner reminiscent of Pavlov's dogs. The findings, published today in the journal Science, may help scientists better understand compulsive eating disorders and substance addiction.
    Russian scientist Ivan Pavlov conditioned his dogs to associate the sound of a bell with food. Eventually, the animals would drool in response to a ring, even when no reward was available. Jay A. Gottfried and his colleagues at the Wellcome Department of Imaging Neuroscience trained people undergoing brain scans to link abstract images on a computer scene with either the smell of vanilla or peanuts. After an eight-minute training period, the subjects showed heightened levels of activity in areas known to be part of the brain's reward circuitry, the amygdala and the orbitofrontal cortex (OFC), associated with the pictures alone. The researchers then instructed the patients to eat as much vanilla ice cream or peanut butter sandwiches as they desired, without becoming uncomfortably full. When the participants were retested using the MRI machine, the scientists found that the image associated with the food they had just eaten evoked a lower response than it did before the snack. The images linked to the other food, in contrast, continued to trigger a hunger response.

    The results suggest that our brains can put the brakes on our desires for certain foods once our cravings have been satisfied. The authors hypothesize that malfunctions in this mechanism could be a driving force behind compulsive eating or addictions. For example, sufferers of Kluver-Bucy syndrome--who often gorge themselves or resort to eating nonfood items--have damage to brain regions including the amygdala and the OFC. "You could conjecture that a similar thing may be going on in certain eating disorders," Gottfried notes, "where the routine breaks on the whole system are tweaked somehow, so they're no longer responding to normal cues."

    --Sarah Graham

  • #2
    SCIENCE NEWS
    August 22, 2003

    Hungry Humans React Like Pavlov's Dogs


    Most people would probably consider their tastes more discerning than those of the family pet. But according to new research, humans can be trained to crave food in a manner reminiscent of Pavlov's dogs. The findings, published today in the journal Science, may help scientists better understand compulsive eating disorders and substance addiction.
    Russian scientist Ivan Pavlov conditioned his dogs to associate the sound of a bell with food. Eventually, the animals would drool in response to a ring, even when no reward was available. Jay A. Gottfried and his colleagues at the Wellcome Department of Imaging Neuroscience trained people undergoing brain scans to link abstract images on a computer scene with either the smell of vanilla or peanuts. After an eight-minute training period, the subjects showed heightened levels of activity in areas known to be part of the brain's reward circuitry, the amygdala and the orbitofrontal cortex (OFC), associated with the pictures alone. The researchers then instructed the patients to eat as much vanilla ice cream or peanut butter sandwiches as they desired, without becoming uncomfortably full. When the participants were retested using the MRI machine, the scientists found that the image associated with the food they had just eaten evoked a lower response than it did before the snack. The images linked to the other food, in contrast, continued to trigger a hunger response.

    The results suggest that our brains can put the brakes on our desires for certain foods once our cravings have been satisfied. The authors hypothesize that malfunctions in this mechanism could be a driving force behind compulsive eating or addictions. For example, sufferers of Kluver-Bucy syndrome--who often gorge themselves or resort to eating nonfood items--have damage to brain regions including the amygdala and the OFC. "You could conjecture that a similar thing may be going on in certain eating disorders," Gottfried notes, "where the routine breaks on the whole system are tweaked somehow, so they're no longer responding to normal cues."

    --Sarah Graham

    Comment


    • #3
      Classical conditioning

      Classical conditioning (also Pavlovian conditioning or respondent conditioning) is a type of associative learning found in animals. These associations are formed by pairing two stimuli--what Ivan Pavlov described as the learning of conditioned behavior-- to condition an animal to give a certain response. The simplest form of classical conditioning is reminiscent of what Aristotle would have called the law of contiguity which states that: "When two things commonly occur together, the appearance of one will bring the other to mind."



      Overview

      The typical paradigm for classical conditioning involves repeatedly pairing a neutral stimulus with an unconditioned stimulus.

      An unconditioned stimulus is a stimulus that elicits a response--known as an unconditioned response--that does not need to be learned by the animal. The relationship between the unconditioned stimulus and unconditioned reponse is known as the unconditioned (or unconditional) reflex. The conditioned stimulus, or conditional stimulus, is an initially neutral stimulus that elicits a response--known as a conditioned response--that is learned by the animal. Conditioned stimuli are associated psychologically with conditions such as anticipation, satisfaction (both immediate and prolonged), and fear. The relationship between the conditioned stimulus and conditioned reponse is known as the conditioned (or conditional) reflex.

      In classical conditioning, when the unconditioned stimulus is repeatedly or strongly paired with a neutral stimulus the neutral stimulus becomes a conditioned stimulus and elicits a conditioned response



      Pavlov's experiment

      The most famous example of classical conditioning involved the salivary conditioning of Pavlov's dogs. Pavlov's dogs naturally salivated to food. Pavlov therefore called the one-to-one correlation between the unconditioned stimulus (food) and the unconditioned response (salivation) an unconditional reflex. If a tone (generated by a tuning fork, for example) was reliably sounded for a few seconds before food, however, the tone eventually came to elicit salivation even when the tone was presented without the food. Because the one-to-one correlation between the conditioned stimulus (tone) and the conditioned response (salivation) involved learning, Pavlov referred to this relationship as a "conditional reflex". The conditional reflex (food-related behaviour elicited by a stimulus that has been reliably paired with food) is said to be developed through classical conditioning.
      The origins of the two reflexes are different. The food (unconditional stimulus) [UCS] causing salivation (unconditional response) [UCR] reflex has its origins in the evolution of the species. The tone (conditional stimulus) [CS] causing salivation (conditional response) [CR] reflex has its origins in the experience of the individual animal.


      Behavioral therapies based on classical conditioning

      In human psychology, implications for therapies and treatments using classical conditioning differ from operant conditioning. Therapies associated with classical conditioning are aversion therapy, flooding, systematic desensitization, and implosion therapy. Implosion therapy and "flooding" involve forcing the individual to face an object/situation giving rise to anxiety; both of these techniques have been criticized for being unethical since they have the potential to cause trauma.

      Classical conditioning is short-term, usually requiring less time with therapists and less effort from patients, unlike humanistic therapies. The therapies mentioned in the last paragraph are intended to cause either aversive feelings toward something, or to reduce the aversion altogether. Classical conditioning is based on a repetitive behaviour system.



      Aversion therapy

      This is a form of psychological therapy that is designed to eliminate sexual behaviour by associating an aversive stimulus such as nausea with ***. Because the aversive stimulus performs as a UCS and produces a UCR, the association between the stimulus and behaviour leads to the same consequences each time. If the treatment has worked, the patient will not have a complusion to engage in such behaviours again. This sort of treatment has been used to treat alcoholism and drug addiction as well as--controversially--homosexuality and sexual perversions. Adams et al. (1981), states that these controversial treatments involved administering electric shocks to homosexuals to reduce the response to male nudes, and encouraging a heterosexual response to female nudes.



      Systematic desensitization

      Patients might learn that the object of their phobias or fears are not so fearful if they can safely relive the feared stimulus. However anxiety often obstructs such recovery. This obstruction is overcome by reintroducing the fear-producing object gradually. A person imagines a series of advancing fearful situations while the person is languid. The responses of irrational fear to the object are eventually rendered incompatible--known as reciprocal inhibition--and the fear is eventually removed if the therapy is performed correctly.

      ______________________________________

      Pavlov, I. P. (1927). Conditioned reflexes. (G. V. Anrep, Trans.). London: Oxford University Press.

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