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  • Motivation

    1. 1. Mechanisms of Motivation
    2. 2. Motivation and Incentives <ul><li>Motivation - factors within and outside an organism that cause it to behave a certain way at a certain time </li></ul><ul><li>Motivational state or drive - an internal condition, which can change over time, that orients an individual to a specific set of goals (e.g., hunger, thirst, sex, curiosity) </li></ul><ul><li>Incentives - goals or reinforcers in the external environment (e.g., good grades, food, a mate) </li></ul>
    3. 3. Drives as Tissue Needs <ul><li>Homeostasis - the constancy of internal conditions that the body must actively maintain </li></ul><ul><li>Drives may be an upset in homeostasis, inducing behavior to correct the imbalance </li></ul><ul><li>Animals do behave in accordance with their tissue needs (e.g., increasing or decreasing caloric intake, drive for salt) </li></ul><ul><li>However, homeostasis cannot explain all drives </li></ul>
    4. 4. Types of Drives <ul><li>Regulatory drives - helps preserve homeostasis (e.g., hunger, thirst, oxygen) </li></ul><ul><li>Nonregulatory drives - serve other purposes (e.g., sex, achievement) </li></ul>
    5. 5. Drives as States of the Brain <ul><li>Central state theory of drives - different drives correspond to neural activity in different sets of neurons in the brain </li></ul><ul><li>Central drive system - set of neurons in which activity constitutes a drive </li></ul>
    6. 6. Drives as States of the Brain <ul><li>Techniques for studying central drive systems include lesions and stimulation </li></ul>Connecting Socket Electrode Brain
    7. 7. Drives as States of the Brain <ul><li>The hub of many central drive systems lies in the hypothalamus </li></ul>Cerebral cortex Portion of limbic system Hypotahlamus Pituitary gland Brainstem
    8. 8. Hunger Drive <ul><li>Two areas of the hypothalamus, the lateral and ventromedial areas, play a central role in the hunger drive </li></ul>Hypothalamus Hypothalamus
    9. 9. Lateral Area <ul><li>Electrical lesions to tract of axons connecting brainstem, hypothalamus and basal ganglia cause a loss of all goal-directed behavior </li></ul><ul><li>Stimulation causes drives in response to available incentives </li></ul>Hypothalamus Hypothalamus
    10. 10. Lateral Area <ul><li>However, chemical lesions to specific cell bodies reduce hunger drive, but do not abolish it - most other drives appear normal </li></ul>Hypothalamus Hypothalamus
    11. 11. Ventromedial Area <ul><li>Lesions alter digestive and metabolic processes </li></ul><ul><li>Food is converted into fat rather than energy molecules, causing animal to eat much more than normal and gain weight </li></ul>Hypothalamus Hypothalamus
    12. 12. Hunger Drive <ul><li>Other stimuli that act on the brain to increase or decrease hunger include </li></ul><ul><ul><li>satiety signals from the stomach </li></ul></ul><ul><ul><li>signals indicating the amount of food molecules in the blood </li></ul></ul><ul><ul><li>leptin, a hormone indicating the amount of fat in the body </li></ul></ul><ul><ul><li>the appetizer effect </li></ul></ul>
    13. 13. Research on Weight Regulation and Dieting <ul><li>No consistent personality trait differences found between obese and non-obese people (e.g., willpower, anxiety) </li></ul><ul><li>Dieters and obese are more likely to eat in response to stress than non-dieters </li></ul><ul><li>Family environment of little importance in determining body weight - genetics plays a large role </li></ul><ul><li>Number of fat-storage cells is a major determinant of body weight </li></ul>
    14. 14. Research on Weight Regulation and Dieting <ul><li>Fat cells are determined by genetics and food intake </li></ul><ul><li>They increase with weight gain, but merely shrink with weight loss - may stimulate hunger </li></ul><ul><li>Weight loss causes a decline in basal metabolism </li></ul>Fat cells Normal diet High-fat diet Return to normal diet
    15. 15. Effects of Culture and Habits on Body Weight <ul><li>Settling point - cluster of genetic and environmental factors that cause a person’s weight to settle within a given range </li></ul><ul><li>Weight can be affected by factors like diet, exercise, and daily habits (e.g., stairs instead of elevator) </li></ul>
    16. 16. Sex Drive <ul><li>Increased production of testosterone and estrogen at puberty is responsible for physical differentiation </li></ul><ul><li>Increased secretion of DHEA, primary adrenal sex hormone, is responsible for sexual feelings </li></ul>Final maturation of ovaries in females Final maturation of testes in males First sexual attraction in both sexes
    17. 17. Male Sex Drive <ul><li>Testosterone maintains sex drive in adult males </li></ul><ul><ul><li>castration decreases drive </li></ul></ul><ul><ul><li>testosterone injections or implantation to medial preoptic area restores drive </li></ul></ul>
    18. 18. Female Sex Drive <ul><li>Estrous cycle controls drive in nonhuman mammals </li></ul><ul><ul><li>removal of ovaries abolishes drive, while hormone injections restore it </li></ul></ul><ul><li>Also, lesions to ventromedial area abolish drive, while injection or implantation restores drive </li></ul>
    19. 19. Female Sex Drive <ul><li>Female monkeys and apes depend less on hormones for sexual behavior </li></ul><ul><li>Human female sex drive may not be consistently affected by hormone cycle at all </li></ul><ul><ul><li>ovarian hormones play small role </li></ul></ul><ul><ul><li>adrenal hormones like DHEA and testosterone play larger role </li></ul></ul>
    20. 20. Early Effects of Testosterone <ul><li>Presence of testosterone during critical period will cause rudimentary genitals of fetus to develop into male structures </li></ul><ul><li>Testosterone acts in brain to promote development of neural systems for male sex drive and inhibit systems for female drive </li></ul><ul><li>Absence causes development of female structures </li></ul><ul><li>Stressful events experienced by pregnant rats reduce level of prenatal testosterone </li></ul>
    21. 21. Human Sexual Orientation <ul><li>Orientation is an early-emerging, ingrained aspect of the self that probably does not change </li></ul><ul><li>No consistent relationship between orientation and childhood experiences (e.g., parenting, abuse, sexual experience) </li></ul><ul><li>Controversial findings suggest a possible relationship among prenatal stress, androgens, and the development of brain systems that play a role in sexual attraction </li></ul>
    22. 22. Reward Pathways in the Brain <ul><li>Medial forebrain bundle runs from the midbrain through the lateral area of the hypothalamus into the nucleus accumbens in the basal ganglia </li></ul><ul><ul><li>neurons in this tract secrete dopamine </li></ul></ul><ul><ul><li>animals will self-stimulate this pathway </li></ul></ul><ul><ul><li>euphoria-producing drugs affect the level of dopamine in this tract </li></ul></ul><ul><ul><li>evolved to promote survival and reproduction </li></ul></ul>