1 Mechanisms of Motivation

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

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

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

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

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

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

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

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

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

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

12 Hunger Drive zOther stimuli that act on the brain to increase or decrease hunger include ysatiety signals from the stomach ysignals indicating the amount of food molecules in the blood yleptin, a hormone indicating the amount of fat in the body ythe appetizer effect

13 Research on Weight Regulation and Dieting zNo consistent personality trait differences found between obese and non-obese people (e.g., willpower, anxiety) zDieters and obese are more likely to eat in response to stress than non-dieters zFamily environment of little importance in determining body weight - genetics plays a large role zNumber of fat-storage cells is a major determinant of body weight

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

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

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

17 Male Sex Drive zTestosterone maintains sex drive in adult males ycastration decreases drive ytestosterone injections or implantation to medial preoptic area restores drive

18 Female Sex Drive zEstrous cycle controls drive in nonhuman mammals yremoval of ovaries abolishes drive, while hormone injections restore it zAlso, lesions to ventromedial area abolish drive, while injection or implantation restores drive

19 Female Sex Drive zFemale monkeys and apes depend less on hormones for sexual behavior zHuman female sex drive may not be consistently affected by hormone cycle at all yovarian hormones play small role yadrenal hormones like DHEA and testosterone play larger role

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

21 Human Sexual Orientation zOrientation is an early-emerging, ingrained aspect of the self that probably does not change zNo consistent relationship between orientation and childhood experiences (e.g., parenting, abuse, sexual experience) zControversial 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 zMedial forebrain bundle runs from the midbrain through the lateral area of the hypothalamus into the nucleus accumbens in the basal ganglia yneurons in this tract secrete dopamine yanimals will self-stimulate this pathway yeuphoria-producing drugs affect the level of dopamine in this tract yevolved to promote survival and reproduction