Mechanisms of Motivation

1. Mechanisms of Motivation

2. Motivation and Incentives • Motivation - factors within and outside an organism that cause it to behave a certain way at a certain time • 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) • Incentives - goals or reinforcers in the external environment (e.g., good grades, food, a mate)

3. Drives as Tissue Needs • Homeostasis - the constancy of internal conditions that the body must actively maintain • Drives may be an upset in homeostasis, inducing behavior to correct the imbalance • Animals do behave in accordance with their tissue needs (e.g., increasing or decreasing caloric intake, drive for salt) • However, homeostasis cannot explain all drives

4. Types of Drives • Regulatory drives - helps preserve homeostasis (e.g., hunger, thirst, oxygen) • Nonregulatory drives - serve other purposes (e.g., sex, achievement)

5. Drives as States of the Brain • Central state theory of drives - different drives correspond to neural activity in different sets of neurons in the brain • Central drive system - set of neurons in which activity constitutes a drive

6. Connecting Socket Electrode Brain Drives as States of the Brain • Techniques for studying central drive systems include lesions and stimulation

7. Cerebral cortex Hypotahlamus Portion of limbic system Pituitary gland Brainstem Drives as States of the Brain • The hub of many central drive systems lies in the hypothalamus

8. Hypothalamus Hypothalamus Hunger Drive • Two areas of the hypothalamus, the lateral and ventromedial areas, play a central role in the hunger drive

9. Hypothalamus Hypothalamus Lateral Area • Electrical lesions to tract of axons connecting brainstem, hypothalamus and basal ganglia cause a loss of all goal-directed behavior • Stimulation causes drives in response to available incentives

10. Hypothalamus Hypothalamus Lateral Area • However, chemical lesions to specific cell bodies reduce hunger drive, but do not abolish it - most other drives appear normal

11. Hypothalamus Hypothalamus Ventromedial Area • Lesions alter digestive and metabolic processes • Food is converted into fat rather than energy molecules, causing animal to eat much more than normal and gain weight

12. Hunger Drive • Other stimuli that act on the brain to increase or decrease hunger include • satiety signals from the stomach • signals indicating the amount of food molecules in the blood • leptin, a hormone indicating the amount of fat in the body • the appetizer effect

13. Research on Weight Regulation and Dieting • No consistent personality trait differences found between obese and non-obese people (e.g., willpower, anxiety) • Dieters and obese are more likely to eat in response to stress than non-dieters • Family environment of little importance in determining body weight - genetics plays a large role • Number of fat-storage cells is a major determinant of body weight

14. Fat cells Normal diet High-fat diet Return to normal diet Research on Weight Regulation and Dieting • Fat cells are determined by genetics and food intake • They increase with weight gain, but merely shrink with weight loss - may stimulate hunger • Weight loss causes a decline in basal metabolism

15. Effects of Culture and Habits on Body Weight • Settling point - cluster of genetic and environmental factors that cause a person’s weight to settle within a given range • Weight can be affected by factors like diet, exercise, and daily habits (e.g., stairs instead of elevator)

16. First sexual attraction in both sexes Final maturation of testes in males Final maturation of ovaries in females Sex Drive • Increased production of testosterone and estrogen at puberty is responsible for physical differentiation • Increased secretion of DHEA, primary adrenal sex hormone, is responsible for sexual feelings

17. Male Sex Drive • Testosterone maintains sex drive in adult males • castration decreases drive • testosterone injections or implantation to medial preoptic area restores drive

18. Female Sex Drive • Estrous cycle controls drive in nonhuman mammals • removal of ovaries abolishes drive, while hormone injections restore it • Also, lesions to ventromedial area abolish drive, while injection or implantation restores drive

19. Female Sex Drive • Female monkeys and apes depend less on hormones for sexual behavior • Human female sex drive may not be consistently affected by hormone cycle at all • ovarian hormones play small role • adrenal hormones like DHEA and testosterone play larger role

20. Early Effects of Testosterone • Presence of testosterone during critical period will cause rudimentary genitals of fetus to develop into male structures • Testosterone acts in brain to promote development of neural systems for male sex drive and inhibit systems for female drive • Absence causes development of female structures • Stressful events experienced by pregnant rats reduce level of prenatal testosterone

21. Human Sexual Orientation • Orientation is an early-emerging, ingrained aspect of the self that probably does not change • No consistent relationship between orientation and childhood experiences (e.g., parenting, abuse, sexual experience) • Controversial findings suggest a possible relationship among prenatal stress, androgens, and the development of brain systems that play a role in sexual attraction

22. Reward Pathways in the Brain • Medial forebrain bundle runs from the midbrain through the lateral area of the hypothalamus into the nucleus accumbens in the basal ganglia • neurons in this tract secrete dopamine • animals will self-stimulate this pathway • euphoria-producing drugs affect the level of dopamine in this tract • evolved to promote survival and reproduction