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PsychSim 5: HUNGER AND THE FAT RAT Name: Section: Date: This activity provides a simulated experiment on weight regulation in rats. The Hypothalamus What are the two techniques used to study hypothalamic dysfunction? How do they differ? Electrolytic surgery, involves inserting a thin electrode into a selected region of the brain. After the electrode is in place, an electrical current is passed through the uninsulated tip of the electrode. There are two different ways to study hypothalamic dysfunction using this technique. Stimulation—If the electrical current passed through the electrode is weak, the target region of the brain is stimulated but not damaged. Generally, this stimulation crudely activates the type of behavior controlled by the target region; if the target region’s function was to inhibit a behavior, then that behavior will occur less frequently during the stimulation. Destruction—If the electric current passed through the electrode is strong, the target region of the brain is damaged. This destruction is called a lesion. A lesion generally suppresses or disrupts the type of behavior associated with the target region; if the target region’s function was to inhibit a behavior, then that behavior will occur more frequently or in an uncontrolled fashion after the lesion. Experimental Simulation What conclusions were you able to draw about the effects of the following procedures on the experimental rats: Stimulation of the lateral hypothalamus (LH)? Causes overeating Destruction of the LH? Causes undereating. Stimulation of the ventromedial hypothalamus (VMH)? Causes undereating Destruction of the VMH? Causes overeating What did you learn from this experiment about these two regions of the hypothalamus? That the LH is a “hunger center”: destroying it leads the rat to starve, while stimulating it will cause a rat to begin eating, even if it isn’t the least bit hungry. Also, that the VMH is a “satiety center”: destroying it leads to a rat that eats enormous quantities of food, while stimulating it causes a hungry rat to stop eating. Some Cautions What are the two problems with a simple conclusion to this research question? 1. The rat with VMH destruction did not keep on gaining weight indefinitely; instead, the rat appeared to level off after about 40 days at a new, higher, but stable weight. Rats with LH destruction also reach a lower but stable weight level if they can be kept alive until they recover from the surgery. This suggests that damage to the VMH or LH may merely readjust the set-point for the system that maintains body weight, rather than destroying the rat’s ability to feel hungry or to feel satisfied. 2. Other research has found that similar disturbances in eating behavior can be produced by damage or stimulation to other regions of the rat’s brain. This strongly suggests that the VMH and LH may be merely links in a complicated chain of neural networks. If any one of the links is stimulated or damaged, the pattern of eating behavior will change.
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