Motivation and Emotion PDF

Final PDF to printer CHAPTER 11 CHAPTER OUTLINE Motivation and Emotion PERSPECTIVES ON MOTIVATION ACHIEVEMENT MOTIVATION Instinct Theory and Evolutionary Psychology Homeostasis and Drive Theory Incentive and Expectancy Theories Psychodynamic and Humanistic Theories The Thrill of Victory, the A...

Final PDF to printer CHAPTER 11 CHAPTER OUTLINE Motivation and Emotion PERSPECTIVES ON MOTIVATION ACHIEVEMENT MOTIVATION Instinct Theory and Evolutionary Psychology Homeostasis and Drive Theory Incentive and Expectancy Theories Psychodynamic and Humanistic Theories The Thrill of Victory, the Agony of Defeat Achievment Goal Theory Achievement Needs and Situational Factors Family and Cultural Influences HUNGER AND WEIGHT REGULATION MOTIVATIONAL CONFLICT The Physiology of Hunger THE NATURE AND FUNCTIONS OF EMOTION Frontiers: Excessive Exercise: Activity Anorexia Psychological Aspects of Hunger Environmental and Cultural Factors Obesity The Adaptive Value of Emotion The Nature of Emotion Applications: The Battle to Control Eating and Weight SEXUAL MOTIVATION Sexual Behaviour: Patterns and Changes The Physiology of Sex The Psychology of Sex Cultural and Environmental Influences Sexual Orientation Focus on Neuroscience: The Neuroscience of Affective Style THEORIES OF EMOTION The James-Lange Somatic Theory The Cannon-Bard Theory Cognitive-Affective Theories Research Foundations: Cognition-Arousal Relations One can never consent to creep when one feels an impulse to soar. —Helen Keller What are the issues here? What do we need to know? Where can we find the information to answer these questions? pas77416_ch11_380-428.indd 380 Dr. Larry Farwell, a former member of the Harvard Medical School, has developed a new technique for determining guilt or innocence. “Brain fingerprinting” involves the monitoring of brainwaves to determine whether or not a suspect has details of a crime or other information stored in the brain. Suspects are shown words or images that would be accessible only to someone who was actually at the scene of the crime. By monitoring brainwaves, the investigator can determine whether or not the suspect recognizes these images. 15/11/13 10:38 AM Final PDF to printer Dr. Farwell’s testimony was instrumental in exonerating Terry Harrington, a convicted murderer who was serving a life sentence in Iowa. Brain fingerprinting revealed that the information in Harrington’s brain did not match the details of the crime but, in fact, were consistent with his alibi. Unlike polygraph examinations, brain fingerprinting has been ruled admissible in U.S. courts. T he term motivation often triggers images of people who persevere to attain their dreams and stretch the boundaries of human achievement. But to psychologists, motivational issues are broader. What motivates eating, sexual behaviour, thrill seeking, and affiliation? Motivation is a process that influences the direction, persistence, and vigour of goal-directed behaviour. The word motivation derives from the Latin term meaning “to move,” and psychologists who study motivation identify factors that move us toward our goals, whether they are obtaining food, a mate, success, or even peace and quiet (see the Frontiers feature later in this chapter). PERSPECTIVES ON MOTIVATION Psychology’s diverse theoretical perspectives view motivation through different lenses. Let’s examine some of their basic motivational concepts. heredity accounts for differences among people in many aspects of motivated behaviour, such as desire for security (Woody, & Szechtman, 2011), or even, as studied by James Olson of the University of Western Ontario, attitudes toward reading books, playing organized sports, and riding roller coasters (Olson, Vernon, Harris, & Jang, 2001). Modern evolutionary psychologists propose that many “psychological” motives have evolutionary underpinnings that are expressed through the actions of genes (Buss, 2007; Palmer & Palmer, 2002). From this perspective, the adaptive significance of behaviour is a key to understanding motivation. For example, why are we such social creatures? Presumably, affiliation produced survival advantages—such as shared resources and protection against predators—that afforded our ancestors a greater opportunity to pass on their genes to successive generations. Over the ages the genes of “affiliative people” made up an increasing part of the human gene pool, and we became biologically predisposed to be social rather than reclusive. Instinct Theory and Evolutionary Psychology Homeostasis and Drive Theory Darwin’s theory of evolution inspired early psychological views that instincts motivate much of our behaviour. An instinct is an inherited predisposition to behave in a specific and predictable way when exposed to a particular stimulus. Instincts have a genetic basis, are found universally among all members of the species, do not depend on learning, and have survival value for the organism. William James (1890) proposed about three dozen human instincts, and by the 1920s, researchers had proposed thousands (Atkinson, 1964). Human instinct theories faded because there was little evidence to support them and they often relied on circular reasoning. Why are people greedy? Because greed is an instinct. How do we know that greed is an instinct? Because people are greedy. This explains nothing. Today, scientists examine hereditary contributions to human motivation more productively. By conducting twin and adoption studies, behaviour geneticists seek to establish how strongly Your body’s biological systems are delicately balanced to ensure survival. For example, when you are hot, your body automatically tries to cool itself by perspiring. When you are cold, your body generates warmth by shivering. In 1932, Walter Cannon proposed the concept of homeostasis, a state of internal physiological equilibrium that the body strives to maintain. Maintaining homeostasis requires a sensory mechanism for detecting changes in the internal environment, a response system that can restore equilibrium, and a control centre that receives information from the sensors and activates the response system (Figure 11.1). The control centre functions somewhat like the thermostat in a furnace or an airconditioning unit. Once the thermostat is set at a fixed temperature, or set point, the sensors detect significant temperature changes in either direction. The control unit responds by turning on the furnace or the air conditioner until the sensor indicates that pas77416_ch11_380-428.indd 381 1. According to evolutionary psychologists, how does the concept of adaptive significance help us understand human motivation? 15/11/13 10:38 AM Final PDF to printer 382 CHAPTER ELEVEN Control centre Response system Sensors Internal state FIGURE 11.1 Your body’s internal environment is regulated by homeostatic mechanisms. Sensors detect bodily changes and send this information to a control centre, which in turn regulates a response system that restores bodily equilibrium. 2. How are homeostatic and drive concepts of motivation related? 3. According to expectancy × value theory, why might people respond differently to the same incentive? the set point temperature has been restored, and then turns it off. Homeostatic regulation also can involve learned behaviours. When we’re hot, we not only perspire, but also may seek a shady place or deliciously cool drink. According to Clark Hull’s (1943, 1951) influential drive theory of motivation, physiological disruptions to homeostasis produce drives, states of internal tension that motivate an organism to behave in ways that reduce this tension. Drives such as hunger and thirst arise from tissue deficits (e.g., lack of food and water) and provide a source of energy that pushes an organism into action. Hull, a prominent learning theorist, proposed that reducing drives is the ultimate goal of motivated behaviour. Homeostatic models currently are applied to many aspects of motivation, such as the regulation of hunger, thirst, body temperature, weight, and sleep (Woods & Seeley, 2002). Drive theory is, however, less influential than in the past. For one thing, people often behave in ways that seem to increase rather than reduce states of arousal, as when people skip meals to diet or flock to tension-generating horror movies. Incentive and Expectancy Theories Whereas drives are viewed as internal factors that “push” organisms into action, incentives represent environmental stimuli that “pull” an organism toward a goal. To a student, a good grade can be an incentive for studying. Incentive theories focus attention on external stimuli that motivate behaviour, though historically the concepts of incentives and drives were pas77416_ch11_380-428.indd 382 often linked. Clark Hull (1943, 1951) argued that all reinforcement involves some kind of biological drive reduction (e.g., food is an incentive because it reduces the drive of hunger), but this view is no longer held. Modern incentive theory emphasizes the “pull” of external stimuli and how stimuli with high incentive value can motivate behaviour, even in the absence of biological need. We have all had the experience of finishing a meal, and hence having no biological need for more food, but quite happily eating dessert when someone places our favourite cake or pie on the table. In this situation, behaviour is motivated not by biological need but by the incentive value of the external stimulus (the dessert). Incentive theories of motivation have been powerfully applied to the study of drug abuse (Stewart, 2000; Stewart & Wise, 1992). An incentive theory of drug use argues that seeking and administering a drug is motivated by the positive incentive value of the drug’s effect. Heroin users, for example, will find and inject heroin because the drug makes them feel good, not because of a biological heroin drive or a desire to escape withdrawal. Why is it, however, that people often respond differently to the same incentive? In part to address such questions, expectancy theories of motivation include the value of incentives, but take a cognitive perspective. Incentive theories had more in common with classical conditioning (e.g., Stewart, 2000) than with cognition, but expectancy theory has broken from this tradition and given a larger role to cognition (Erez & Isen, 2002). Consider James, Lenora, and Harrison, students in a calculus class who have similar math aptitude. Yet James studies hard in hopes of getting an A, whereas Lenora and Harrison put in just enough effort to pass with a C. How can we explain the differences in the behaviour of these three students? According to the cognitive perspective, the answer lies in their thoughts about this situation. One cognitive approach, called expectancy × value theory (or simply expectancy theory), proposes that goaldirected behaviour is jointly determined by two factors: the strength of the person’s expectation that particular behaviours will lead to a goal, and the value the individual places on that goal—often called incentive value (Brehm & Self, 1989). These two factors are multiplied, producing the following equation: Motivation 5 expectancy × incentive value. James works hard because he believes that the more you study, the greater the probability of getting an A, and he values an A highly. Lenora also believes that studying hard will lead to an A, but getting an A holds little value for her in this course. In contrast, Harrison values an A, but believes that because the tests are tricky, studying hard is unlikely to produce a high grade. 15/11/13 10:38 AM Final PDF to printer Motivation and Emotion Many cognitive theorists distinguish between extrinsic motivation, performing an activity to obtain an external reward or avoid punishment, and intrinsic motivation, performing an activity for its own sake—because you find it enjoyable or stimulating. Students who read their textbooks only because they want to get good grades are showing extrinsic motivation. Students who read their textbooks because they find them interesting and want to learn more are showing intrinsic motivation. Can external incentives ever decrease motivation? According to the overjustification hypothesis, giving people extrinsic rewards to perform activities that they intrinsically enjoy may “overjustify” that behaviour and reduce intrinsic motivation (Bright & Penrod, 2009). In essence, if we begin to perceive that we are performing for the extrinsic rewards rather than for enjoyment, the rewards will turn “play” into “work,” and it might be difficult to return to “play” if those rewards are no longer available. It is surprisingly common for people to report that an activity is no longer as enjoyable once they begin to be paid for it. A student who, for example, makes jewellery as a hobby (i.e., she simply enjoys the activity) and then begins to sell the jewellery will commonly report a marked decrease in the intrinsic pleasure of the activity. distinguished between deficiency needs, which are concerned with physical and social survival, and growth needs, which are uniquely human and motivate us to develop our potential. He proposed the concept of a need hierarchy, a progression of needs containing deficiency needs at the bottom and growth needs at the top (Figure 11.2). Once our basic physiological needs are satisfied, we focus on our needs for safety and security. After these needs are met, we turn our attention to needs at the next highest level, and so on. Self-actualization represents the need to fulfill our potential, and it is the ultimate human motive. To echo an army recruiting slogan, self-actualization is striving to “be all that you can be.” Critics question the validity of Maslow’s need hierarchy and believe that the concept of “selfactualization” is vague (Heylighen, 1992). How does the hierarchy explain why prisoners of war endure torture rather than betray their comrades or why millions of women live in constant hunger to be thin? Still, the model draws valuable attention to the human desire for growth, incorporates a wide range of psychological and biological motives, and has influenced thinking in such diverse fields as philosophy, education, and business (Muchinsky, 2000). 4. Explain Maslow’s concept of a need hierarchy. Do you agree with this model? Thinking critically Psychodynamic and Humanistic Theories IS MASLOW’S NEED HIERARCHY VALID? The psychodynamic and humanistic perspectives view motivation within a broader context of personality development and functioning, but take radically different approaches. Freud’s (1923) psychoanalytic theory highlighted the motivational underworld. To Freud, much of our behaviour results from a never-ending battle between unconscious impulses struggling for release and psychological defences used to keep them under control. Energy from these unconscious motives—especially from instinctive sexual and aggressive drives—is often disguised and expressed through socially acceptable behaviours. Thus, hidden aggressive impulses may fuel one’s career as a trial lawyer, businessperson, or athlete. Although research offers little support for Freud’s “dual-instinct” model, his work stimulated other psychodynamic theories that highlighted different needs, such as needs for self-esteem and relatedness to other people (Adler, 1927; Kohut, 1977). Today’s diverse psychodynamic theories continue to emphasize that, along with conscious mental processes, unconscious motives and tensions guide how we act and feel (Westen, 1998). Humanist Abraham Maslow believed that psychology’s other perspectives ignored a key motive: our striving for personal growth. Maslow (1954) Does the concept of a need hierarchy, shown in Figure 11.2, make sense to you? How do you feel about the ordering of needs in Maslow’s hierarchy? pas77416_ch11_380-428.indd 383 383 Think about it, and then see the Answers section at the end of the book. A more recent humanistic theory of motivation has been advanced by Edward Deci and Richard Ryan (1985, 2009). Self-determination theory focuses on three fundamental psychological needs: competence, autonomy, and relatedness. People are most fulfilled in their lives when they are able to satisfy these fundamental needs. On the other hand, when these needs are not met, there can be consequences for both psychological and physical well-being (Deci & Ryan, 2009). Competence motivation reflects a human need to master new challenges and perfect skills. This need motivates much exploratory and growth-inducing human behaviour. The need for autonomy (or selfdetermination) is satisfied when people experience their actions as a result of free choice without outside interference. Relatedness refers to our desire to form meaningful bonds with others. At first 5. What are the three needs identified in self-determination theory? 15/11/13 10:38 AM Final PDF to printer 384 CHAPTER ELEVEN es gr Re sio ni f lo r we ne ni ot t me s re ati sfi ed Safety needs security • psychological safety sa ed Belongingness and love needs affiliation • acceptance • affection ne Deficiency needs r we Esteem needs approval • recognition f lo Cognitive needs knowledge • understanding n re sa ed sio Aesthetic needs beauty • symmetry res og Pr Selfactualization Growth needs Physiological needs food • drink FIGURE 11.2 Maslow proposed that needs are arranged in a hierarchy. After meeting our more basic needs, we experience need progression and focus on needs at the next level. If a need at a lower level is no longer satisfied, we experience need regression and focus once again on meeting that lower-level need. Critics wonder whether people might focus on belonging, love, esteem, and higher-level needs even when their physiological and safety needs are not met. What do you think? glance, relatedness may seem opposed to autonomy, but the two actually complement each other. When true relatedness is achieved, people often feel freer to be themselves. Adolescents who feel that their autonomy is acknowledged and supported by their parents feel a strong sense of relatedness to their parents (Ryan & Lynch, 1989). Similarly, workers who are given freedom to develop their own plans (increased autonomy) experience an increased emotional bond with their employer and company (Tremblay et al., 2009). The importance of self-determination theory’s three basic needs has been strongly supported by research. They appear to have independent and additive effects on positive outcomes such as psychological well-being, happiness, worker performance and satisfaction, positive social relationships, and a sense of meaningfulness in life (Deci & Ryan, 2009; Sheldon et al., 2003). The most positive psychological outcome of all results from a balance among the three needs (Milyavskaya et al., 2009). In Review • Motivation is a process that influences the direction, vigour, and persistence of behaviour. Evolutionary psychologists propose that in our ancestral past, motivational tendencies that had adaptive significance were more likely to be passed from one generation to the next, eventually evolving into genetically based predispositions to act in certain ways. • Homeostatic models view motivation as an attempt to maintain equilibrium in bodily systems. Drive theories propose that tissue deficits create drives, such as hunger, that motivate or “push” an organism from within to reduce the deficit and restore homeostasis. pas77416_ch11_380-428.indd 384 • Incentive theories emphasize the role of environmental factors that “pull” people toward a goal. The cognitive expectancy × value theory explains why the same incentive may motivate some people but not others. • Psychodynamic theories emphasize that unconscious motives and mental processes guide much of our behaviour. Humanist Abraham Maslow proposed that needs exist in a hierarchy, from basic biological needs to the ultimate need for self-actualization. • Self-determination theory focuses on three psychological needs: competence, autonomy, and relatedness. 15/11/13 10:38 AM Final PDF to printer Motivation and Emotion In sum, each of these theoretical approaches raises provocative questions about human motivation and has strong proponents and critics, just as some perspectives no doubt resonate more than others with your own views about motivation. Taken together, they underscore the complexity of behaviour and the value of studying it from multiple levels of analysis. We begin that analysis with one of our most basic motives: hunger. HUNGER AND WEIGHT REGULATION If you could give up all food forever and satisfy your hunger and nutritional needs with a daily pill, would you? Eating is a necessity, but for many people it also is one of life’s delicious pleasures. Thus, while biology provides a “push” to eat, the anticipated and actual good taste of food offers a powerful “pull” (Bolles, 1980). Indeed, numerous biological, psychological, and environmental factors regulate our food intake. The Physiology of Hunger Eating and digestion supply the body with the fuel it needs to function and survive. Metabolism is the body’s rate of energy (or caloric) utilization, and about two-thirds of the energy we normally use goes to support basal metabolism, the resting, continuous metabolic work of body cells. Several mechanisms attempt to keep the body in energy homeostasis by regulating food intake (Woods & Seeley, 2002). There are “short-term” signals that start meals by producing hunger and stop food intake by producing satiety (the state in which we no longer feel hungry as a result of eating). Your body also monitors “long-term” signals based on how much body fat you have. These signals adjust appetite and metabolism to compensate for times when you overeat or eat too little in the short term. Before we describe some of these signals, consider three points. First, many of us believe that hunger occurs when we begin to “run low on energy,” and that we feel “full” when immediate energy supplies are restored (Assanand et al., 1998). Your body does monitor its immediate energy supplies, but this information interacts with other signals to regulate food intake. Thus, hunger is not necessarily linked to immediate energy needs (Pinel, 1997; Woods et al., 1998). Second, homeostatic mechanisms are designed to prevent you from “running low” on energy in the first place. In evolutionary terms, an organism that does not eat until its energy supply is low (in any absolute sense) would be at a serious survival disadvantage. pas77416_ch11_380-428.indd 385 385 Finally, researchers believed that there is a set point—an internal physiological standard—around which body weight (or more accurately, our fat mass) is regulated (Powley & Kessey, 1970). This view holds that if we overeat or eat too little, homeostatic mechanisms will return us close to our original weight, our set point. Although this idea is well ingrained in popular culture, some researchers, such as John Pinel at the University of British Columbia, believe it is flawed (Pinel, 1997; Pinel, Assanand, & Lehman, 2000). They propose that, as we gain or lose weight, homeostatic mechanisms kick in and make it harder to keep gaining or losing weight, but do not necessarily return us to our original weight. Over time, we may “settle in” at a new weight. Signals That Start and Terminate a Meal Is hunger produced by those familiar muscular contractions (“hunger pangs”) of an empty stomach? In an early experiment, A.L. Washburn showcased a unique scientific talent: He swallowed a balloon. When it reached his stomach, the balloon was inflated and hooked up to an amplifying device to record his stomach contractions. Washburn then pressed a key every time he felt hungry (Figure 11.3). The findings revealed that Washburn’s stomach contractions did indeed correspond to subjective feelings of hunger (Cannon & Washburn, 1912). But did they cause the “experience” of hunger? Surprisingly, other research indicates that “hunger pangs” do not depend on an empty stomach, or any stomach at all! Animals display hunger and satiety even if all nerves from their stomach to their brain are cut, and people who have had their stomach surgically removed for medical reasons continue to feel hungry and “full” (Brown & Wallace, 1980). Thus, other signals must help to trigger hunger. When you eat, digestive enzymes break food down into various nutrients. One key nutrient is glucose, a simple sugar that is the body’s (and especially the brain’s) major source of immediately usable fuel. After a meal, some glucose is transported into cells to provide energy, but a large portion is transferred to your liver and fat cells, where it is converted into other nutrients and stored for later use. Sensors in the hypothalamus and liver monitor blood glucose concentrations. When blood glucose levels decrease, the liver responds by converting stored nutrients back into glucose. This action produces a drop-rise glucose pattern. The meaning of this drop-rise pattern is not certain, but it may contain information that helps the brain regulate hunger (Campfield, 1997). 6. Describe some physiological signals that initiate hunger. 15/11/13 10:38 AM Final PDF to printer 386 CHAPTER ELEVEN Stomach contractions Time Pangs Respiration Balloon Signal key FIGURE 11.3 A.L. Washburn swallowed a balloon and inflated it in his stomach. A machine recorded stomach contractions by amplifying changes in the pressure on the balloon, and Washburn pressed a telegraph key every time he felt a hunger pang. Hunger pangs occurred when the stomach contracted. Based on Cannon and Washburn, 1912. 7. What physiological signals cause us to stop eating? 8. Explain how leptin regulates appetite. How did scientists learn about leptin’s role? pas77416_ch11_380-428.indd 386 As we eat, several bodily signals combine and ultimately cause us to end our meal. Stomach and intestinal distention are “satiety signals” (Stricker & Verbalis, 1987). The walls of these organs stretch as food fills them up, sending nerve signals to the brain. This does not mean that the stomach literally has to be “full” for us to feel satiated. Nutritionally rich food seems to produce satiety more quickly than an equal volume of less nutritious food, suggesting that some satiety signals respond to food content. Patients who have had their stomachs removed continue to experience satiety not only because of intestinal distention, but also because of chemical signals (Collier & Johnson, 2004). The intestines respond to food by releasing several hormones— called peptides—that help to terminate a meal. For example, CCK (cholecystokinin) is released into your bloodstream by the small intestine as food arrives from the stomach. It travels to the brain and stimulates receptors in several regions that decrease eating. Hungry animals injected with CCK will stop feeding or reduce the size of their meals, and humans who receive small doses of peptides report feeling full after eating less food (Gibbs et al., 1973; Konkle et al., 2000). See Table 11.1. Whereas CCK decreases feelings of hunger, another peptide hormone increases feelings of hunger and eating. Ghrelin is released into the bloodstream by the stomach and small intestine and is now thought to be one of the most important signals for hunger among humans (Schüssler et al., 2012). People given an injection of ghrelin report feeling hungry and, given the opportunity to eat, will consume more food than participants given injections of saline (Schmid et al., 2005). Ghrelin has also been reported to increase thoughts about food and mental images of food, especially the mental image of a favourite meal (Schmid et al., 2005). Your ghrelin levels are highest just before meal-time, they decline rapidly after eating, and then they begin to rise again as the next meal approaches. Ghrelin release can also be triggered by food-related cues, such as pictures of food (Schüssler et al., 2012). Signals That Regulate General Appetite and Weight Fat cells are not passive storage sites for fat. Rather, they actively regulate food intake and weight by secreting leptin, a hormone that decreases appetite (Halaas et al., 1995). As we gain fat, more leptin is secreted into the blood and reaches the brain, where receptor sites on certain neurons detect it. These leptin signals influence neural pathways to decrease appetite and increase energy expenditure (Woods et al., 1998, 2000). See Table 11.1. Leptin is a “background” signal. It does not make us feel “full” like CCK and other satiety signals that respond directly to food intake during a meal. Instead, leptin may regulate appetite by increasing the potency of these other signals (Woods & Seeley, 2002). Thus, as we gain fat and secrete more leptin, we tend to eat less because these mealtime satiety factors make us feel full sooner. As we lose fat and 15/11/13 10:38 AM Final PDF to printer Motivation and Emotion TABLE 11.1 Some of the Signals That Control Eating by Increasing or Decreasing Hunger Signal Source Effect Glucose blood glucose levels monitored by hypothalamus, liver released into bloodstream by intestines secreted into bloodstream by fat cells secreted by neurons within the PVN of the hypothalamus secreted into bloodstream by stomach, small intestine drop-rise pattern increases hunger CCK Leptin Neuropeptide Y Ghrelin 387 secrete less leptin, it takes more food and a greater accumulation of satiety signals to make us feel full. In essence, high leptin levels may tell the brain “There is plenty of fat tissue, so it’s time to eat less.” Evidence for leptin’s important role grew out of research with genetically obese mice (Coleman, 1978; Zhang et al., 1994; Figure 11.4). A gene called the ob gene (ob = obesity) normally directs fat cells to produce leptin, but mice with an ob gene mutation lack leptin. As they gain weight, their brains do not receive this “curb your appetite” signal, and the mice overeat and become obese. Daily leptin injections reduce their appetites and increase their energy expenditure, and the mice become thinner. Another strain of obese mice produces ample leptin, but because of a mutation in a different gene (the db gene), their brain receptors are insensitive to leptin (Chen et al., 1996; Halaas et al., 1995). The “curb your appetite” signal is there, but they can’t detect it, and become obese. Injecting these mice with leptin does not reduce their food intake and weight. Are these specific ob and db gene mutations a major source of human obesity? Probably not, for both genetic conditions seem to be rare in humans (Clement, 1999). However, when they do occur, these conditions are associated with extreme obesity, decreases hunger decreases hunger increases hunger increases hunger suggesting the importance of normal leptin functioning in human weight regulation. Might leptin injections be the “magic bullet” that would help most obese people lose weight? Unfortunately, there is reason for doubt, because obese people already have ample leptin in their blood because of their fat mass (Jequier & Tappy, 1999; Ravussin & Gautier, 1999). For currently unknown reasons, their brains appear to be insensitive to that information. Brain Mechanisms Many parts of the brain—ranging from the primitive brain stem to the lofty cerebral cortex—play a role in regulating hunger and eating (Logue, 1991). But is there a “master control centre”? Early experiments pointed to two regions in the hypothalamus (Stellar, 1954). Areas near the side, called the lateral hypothalamus (LH), seemed to be a “hunger on” centre (Figure 11.5). Electrically stimulating a rat’s Paraventricular nucleus Pituitary Ventromedial hypothalamus FIGURE 11.4 The mouse on the left has an ob gene mutation. Its fat cells fail to produce leptin, and it becomes obese. Leptin injections help such mice return to normal weight, as seen in the mouse on the right. pas77416_ch11_380-428.indd 387 Lateral hypothalamus FIGURE 11.5 Various structures within the hypothalamus play a role in regulating hunger, thirst, sexual arousal, and body temperature. The lateral hypothalamus (LH), ventromedial hypothalamus (VMH), and paraventricular nucleus (PVN) are involved in hunger regulation. 15/11/13 10:38 AM Final PDF to printer 388 CHAPTER ELEVEN Frontiers EXCESSIVE EXERCISE: ACTIVITY ANOREXIA At any one time, in any situation, we have a variety of behaviours we can choose from. We choose one behaviour from a range of possibilities, and as the situation changes we may switch from our previous behaviour to doing something new. Motivated behaviours such as exercise, playing video games, gambling, or eating occur as part of a range of activities in one’s life, and under normal circumstances do not pose any undue threat to the individual. In some situations, however, these behaviours may become problematic. If an individual devotes excessive amounts of time and effort to their chosen activity, their behaviour can create a range of social, psychological, and health problems. One such activity that has been studied experimentally in nonhumans is wheel running by rats. Understanding this behaviour and the mechanisms that control its excessive form may provide insight into how once normal, and even healthy, behaviours can come to dominate an individual’s life. If rats have access to a running wheel, they will spend some of their time running. This behaviour tends to increase in frequency with experience, and, perhaps counterintuitively, it may become excessive if the animal is hungry (Lett, Grant, Koh, & Smith, 2001). As Terry Belke, of Mount Alison University, and David Pierce, of the University of Alberta, have shown, as the body weight of a rat falls, both food and exercise (wheel running) become more reinforcing (Belke & Pierce, 2009). If a rat is allowed limited access to food and unlimited access to a running wheel except during the meal period, a condition called activity anorexia develops (Epling & Pierce, 1992). Over days, animals with access to a running wheel engage in increasing amounts of running; they eat less, lose weight, and, if left in this situation, will starve. The rats with the running wheels do not simply eat too little to compensate for the time spent on the added exercise, they actually eat less than do animals that do not have access to a running wheel. As these animals eat less and lose weight, the amount of wheel running increases, exacerbating the problem. Eating is increasingly suppressed while physical exercise becomes excessive. Activity anorexia highlights some intriguing issues in the study of motivation—how the motivation for a behaviour can increase to the point of endangering an individual’s health and well-being, how two behaviours with different motivations (running and eating) can come to compete with each other, and how a single motivated behaviour, wheel running, can have both aversive and rewarding effects. Many researchers consider activity anorexia to be an animal model of the human eating disorder anorexia nervosa (Epling & Pierce, 1992; Sparkes, Grant, & Lett, 2003). We will discuss eating disorders, including anorexia nervosa, in Chapter 16. Although the mechanisms of activity anorexia are not completely understood, the research program of Dr. Virginia Grant and colleagues at Memorial University of Newfoundland has contributed much to our understanding of activity anorexia. Research by Grant and her colleagues, and others, indicates that wheel running by rats can have both positive and aversive effects; it can act as a reinforcer, but it can also be used as an aversive consequence to generate a conditioned taste aversion (CTA; Figure 11.6a; Lett, Grant, Koh, & Smith, 2001; Lett, Grant, Byrne, & Koh, 2000; Sparkes et al., 2003). As we saw in our earlier discussion of CTAs (see Chapter 7), a taste paired with aversive consequences, such as illness, will lead to a learned (conditioned) aversion to that taste. Reports of conditioned taste aversions with wheel running, however, are not always consistent. Sparkes, Grant, and Lett (2003) investigated one possible explanation for the inconsistent findings with wheel running and the development of a CTA. In this study, rats were given once-daily access to food and were allowed to eat as much as they wanted for 90 minutes. For some animals the food was familiar; it was the same food that they ate prior to the start of the experiment. For some it was a novel food; the first time these animals had access to this food was during the five days that they engaged in wheel running. Sparkes et al. found that animals developed a CTA to the novel food that had been paired with wheel running, but they did not develop a CTA to the familiar food. CTAs typically develop rapidly to novel foods but accrue to familiar foods only slowly. Together with the finding that CTAs developed using wheel running share features with more typically induced CTAs, these findings address an important issue with respect to activity anorexia. Does the wheel running generate an aversion to food and is it the aversion, rather than wheel running itself, that leads to the suppression of eating? A conditioned aversion to foods cannot be responsible for the decrease in food intake with activity anorexia since a CTA did not develop to familiar foods paired with wheel running. Animals that had the familiar food did not develop a CTA, but these animals did show activity anorexia. Thus, the wheel running itself suppresses feeding without necessarily involving a CTA. Since it can be used to develop a conditioned aversion, wheel running must be considered to have some aversive or negative consequences. If wheel running does have aversive or negative consequences, as indicated by the CTA findings, why do animals engage in this behaviour? In a study by Sparkes et al. (2003), continued LH causes it to start eating, and lesioning (damaging or destroying) the LH causes it to refuse to eat, even to the point of starvation (Anand & Brobeck, 1951). pas77416_ch11_380-428.indd 388 In contrast, structures in the lower-middle area, called the ventromedial hypothalamus (VMH), seemed to be a “hunger off ” centre. 15/11/13 10:38 AM Final PDF to printer Motivation and Emotion 70 9 Mean preference score Mean amount consumed (m) 10 8 7 6 5 4 3 2 60 50 40 30 20 10 1 0 0 Paired Unpaired (a) 389 Control (b) Group Saline Group Naloxone FIGURE 11.6 Panel (a) shows the results from a conditioned taste aversion (CTA) experiment. If a taste has been paired with wheel running (Paired), animals will consume less of that substance than do animals who had exposure to the same taste but it was not paired with wheel running (Unpaired), demonstrating a CTA (adapted from Lett, Grant, Koh, & Smith, 2001). Panel (b) shows the results of a CPP experiment with wheel running. If a distinctive location is paired with wheel running, animals will spend more time in that location (Saline group) than if that location is not paired with wheel running (Control group). An opioid antagonist (Naloxone) will block the development of this CPP (adapted from Lett, Grant, & Koh, 2001). A preference score of 50 indicates no preference. wheel running was paired with a distinctive location (a holding cage with distinctive visual cues). Interestingly, the same animals that developed a CTA when wheel running was paired with a novel taste developed a conditioned place preference (CPP) for a location that had been paired with wheel running. That is, the same activity, wheel running, can have both positive (CPP) and aversive (CTA) effects. Although this may be unexpected, other motivationally powerful stimuli, such as amphetamines and opiates, support the development of both conditioned aversions and conditioned preferences. It has been suggested that the rewarding effects of activities such as wheel running involve the endogenous opioids (Lett, Grant, & Koh, 2001), a class of neurotransmitters that have opiate-like effects and include neurotransmitters such as the endorphins (see Chapter 3). A drug called naloxone binds to the same receptors as the opioid neurotransmitter and morphine, but naloxone occupies the receptor without activating it. That is, naloxone is a receptor antagonist that prevents the active substance (endorphin) from having an effect by blocking its access to the receptor. If wheel running has a rewarding effect by activating the brain’s opioid system, then naloxone should block this effect. Lett, Grant, and Koh (2001) found that naloxone did prevent the development of a CPP using wheel running. Naloxone did not change the amount of wheel running significantly, as compared with a saline-injected control, but it did block the rewarding effects (Figure 11.6b). Electrically stimulating the VMH caused even a hungry rat to stop eating, and lesioning the VMH produced gluttons who ate frequently and pas77416_ch11_380-428.indd 389 Further evidence that wheel running activates an opioid neurotransmitter system comes from a study in which animals were tested for a CPP (Lett, Grant, Koh, & Flynn, 2002). Animals that had prior experience with wheel running did not develop a CPP when a distinctive chamber was paired with morphine. Animals without the wheel running experience showed a morphine-induced CPP. That is, the animals with prior wheel running experience appeared to be tolerant to the rewarding effect of morphine, a phenomenon known generally as cross-tolerance. Within psychopharmacology, cross-tolerance is considered to be evidence that a common brain mechanism is involved. The studies of CPP with wheel running and of cross-tolerance to morphine indicate that wheel running activates the brain’s endogenous opioid system, and it is this activation that leads to the rewarding effects of wheel running. Wheel running is a behaviour that increases in frequency with experience, and since there is no necessary satiation (apart from physical exhaustion) this behaviour can come to dominate the animals’ time, even if the excessive wheel running and the accompanying suppression of eating means starvation. Evidence suggests that this behaviour activates the brain’s reward mechanisms. Understanding the changes in motivation that allow some behaviours to become excessive, even to the point of endangering one’s life, is clearly relevant to the current human condition. doubled or tripled their body weight (Hetherington & Ranson, 1942). Medical case studies of people with damage to these hypothalamic areas 15/11/13 10:39 AM Final PDF to printer 390 CHAPTER ELEVEN 9. What evidence suggested that the LH and VMH were hunger “on” and “off” centres? What evidence suggests otherwise? 10. Describe some factors that contribute to the pressure women feel to be thin. also found that normal weight regulation was disrupted (Gazzaniga et al., 1979). As scientists explored further, they learned that, although the LH and VMH played a role in hunger regulation, they were not really “hunger on” and “hunger off ” centres (Pinel, 1997; Schwartz, 1984). For example, rats with LH damage stop eating and lose weight in part because they develop trouble swallowing and digesting, and they become generally unresponsive to external stimuli, not just to food. Moreover, axons from many brain areas funnel into the hypothalamus and then fan out again upon leaving it. Cutting these nerve tracts anywhere along their path—not just within the hypothalamus—duplicates some of the effects of the LH and VMH lesions (Schwartz, 1984). Researchers are examining how various neural circuits within the hypothalamus regulate food intake. Many pathways involve the paraventricular nucleus (PVN), a cluster of neurons packed with receptor sites for various transmitters that stimulate or reduce appetite (Figure 11.5). The PVN appears to integrate several different short-term and longterm signals that influence metabolic and digestive processes (Berthoud, 2002). One transmitter, neuropeptide Y, is a powerful appetite stimulant (Leibowitz, 1992). Rats in one experiment quickly became obese when they received three daily injections of neuropeptide Y into their PVN for ten days. Their food intake doubled, their fat mass tripled, and their total body weight increased sixfold (Stanley et al., 1986). A fascinating finding about leptin and the PVN in rats may help to explain why we become so hungry when trying to lose weight. When leptin reaches the hypothalamus, it seems to inhibit the activity of neurons that release neuropeptide Y into the PVN, and therefore appetite is reduced. But when rats lose fat, less leptin is secreted and therefore neuropeptide Y neurons become more active, increasing appetite (Woods & Seeley, 2002). See Table 11.1. Psychological Aspects of Hunger From a behavioural perspective, eating is positively reinforced by the good taste of food and negatively reinforced by hunger reduction. Cognitively, we develop an expectation that eating will be pleasurable, which becomes an important motivator to seek and consume food. Even the mere thought of food can trigger hunger, as you may find by closing your eyes and concentrating on the aroma, sight, and taste of your favourite dish. Attitudes, habits, and psychological needs also regulate food intake. Have you ever felt “stuffed” after gobbling up part of a meal, yet finished it and even had dessert? Beliefs such as “don’t leave pas77416_ch11_380-428.indd 390 food on your plate” and conditioned habits (“autopilot” snacking while watching TV) may lead us to eat even when we do not feel hungry. Conversely, countless dieters intentionally restrict their food intake even though they are hungry. Especially for women, such food restriction often stems from social pressures to conform to cultural standards of beauty (Figure 11.7). Studies of Playboy magazine centrefolds, beauty pageant contestants, and fashion models indicate a clear trend toward a thinner, leaner, and increasingly unrealistic “ideal” female body shape between the 1950s and 1990s (Owen & Laurel-Seller, 2000). The culturally defined “ideal” female body has changed again in recent years, adding an ultra-fit physique in addition to extreme thinness (Homan et al., 2012). Correspondingly, relative to men, over the past 50 years, women have become increasingly dissatisfied with their body image (Feingold & Mazzella, 1998). A classic study by April Fallon and Paul Rozin (1985) suggests an additional reason why this is so. University women overestimated how thin they needed to be to meet men’s preferences, whereas men overestimated how bulky they should be to match women’s preferences (Figure 11.8). Women also perceived their body shape as heavier than ideal, whereas men viewed their body shape as close to ideal. As Fallon and Rozin noted, “Overall, men’s perceptions serve to keep them satisfied with their figures, whereas women’s perceptions place pressure on them to lose weight” (1985, p. 102). Researchers continue to find results similar to Fallon and Rozin’s (Carlson & McAndrew, 2004; Demarest & Allen, 2000). People who perceive themselves as heavy tend to have lower self-esteem, but this relation is stronger among women than men (Miller & Downey, 1999). According to Barbara Fredrickson and Tomi Ann Roberts’s (1997) objectification theory, Western culture teaches women to view their bodies as objects, much as external observers would. This perspective increases body shame and anxiety, which in turn leads to eating restriction and even eating disorders (Fredrickson et al., 1998). Laboratory experiments suggest that women do indeed restrict eating to restore self-esteem. In one experiment, university women ate less food in the presence of a desirable versus undesirable male, particularly when their feelings of femininity had been publicly threatened beforehand (Mori et al., 1987). The norms that “thin = attractive” and “you can never be too thin” are strongly ingrained by adolescence and have a powerful impact even early in adolescence. As early as the eighth grade, many girls have adopted the belief that they have to be thin to be popular with boys (Halpern et al., 1999), 31/12/13 8:21 AM Final PDF to printer Motivation and Emotion 391 FIGURE 11.7 Throughout much of Western history, a full-bodied woman’s figure was esteemed. This is illustrated by (a) Peter Paul Rubens’s 17th-century painting, The Three Graces, and by (b) actress Lillian Russell, who represented the American ideal of feminine beauty a century ago. In recent decades, the norm of “thin = attractive” has evolved, as illustrated (c) by this contemporary fashion model. and girls as young as ten years old diet to look thinner (McVey et al., 2004). Such social pressures and beliefs can lead to a high level of dissatisfaction with one’s own body. As few as one in five adolescent and young adult females report being happy with their weight, even when body weight is within a normal, healthy range (Halpern et al., 1999; Huon et al., 2002; Kenardy et al., 2001). Environmental and Cultural Factors Although not very sensitive to manipulation of biological variables such as overfeeding, underfeeding, or changes in the caloric density of the diet, people are very sensitive to changes in environmental stimuli, such as portion size, the number of people present during a meal, the amount that others eat, and the variety of foods available (Levitsky, 2005). We will consider a few of the most important environmental variables that influence how much we eat. Food availability is the most obvious environmental regulator of eating. For millions of people who live in poverty or famine-ravaged regions, food scarcity limits consumption. In contrast, pas77416_ch11_380-428.indd 391 abundant low-cost food (including high-fat foods) in many countries contributes to a high rate of obesity among children and adults (Wadden et al., 2002). Food taste, variety, and serving size all powerfully regulate eating. Good-tasting food positively reinforces eating and increases food consumption, but during a meal and from meal to meal, we can become “tired of eating the same thing” and terminate a meal more quickly (Rolls et al., 1981). In contrast, food variety increases consumption, which you know all too well if you attend buffet meals. The amount of food served also influences how much we eat. In one study participants were presented with a macaroni and cheese lunch in one of four different portion sizes (Rolls et al., 2002). Although participants did not differ in self-reported hunger or how much food they predicted they would eat before the lunch, the larger the portion they were given, the more they ate. Those presented with the largest portion size ate, on average, almost 100 grams more macaroni and cheese than those presented with the smallest serving (Figure 11.9). That represents an additional 676 kJ (162 calories) consumed just because of a larger serving size. 11. Identify several environmental and cultural factors that influence eating. 15/11/13 10:39 AM Final PDF to printer 392 CHAPTER ELEVEN 2 2.5 What women rated as ideal 2 3 What women thought men preferred 2.5 3.5 4 3.5 What women actually preferred 5 4.5 5 Women’s self-image What men actually preferred 3 4.5 4 What men thought women preferred Men’s self-image What men rated as ideal FIGURE 11.8 University women overestimated how thin they needed to be to conform to men’s preferences and viewed their own body shape as heavier than ideal. In contrast, men overestimated how bulky they should be to conform to women’s preferences but viewed their body shape as close to ideal. Data from Fallon & Rozin, 1985. Through classical conditioning we learn to associate the smell and sight of food with its taste, and these food cues can trigger hunger. Eating may be the last thing on your mind until your nose Amount eaten (grams) 500 450 400 350 300 250 200 150 100 500 625 750 1000 Portion size (grams) FIGURE 11.9 Participants were presented with a macaroni and cheese lunch in one of four portion sizes, and the amount of food eaten increased with portion size. This was true for both men and women, and for normal-weight and overweight participants (data shown is for the subject groups combined). Data from Rolls et al., 2002. pas77416_ch11_380-428.indd 392 detects the sensuous aroma wafting from a bakery, a pizzeria, or a popcorn machine. Dr. Harvey Weingarten (1983), then at McMaster University, demonstrated that rats that have eaten recently and are not hungry (i.e., they have food available but ignore it) will eat when presented with sounds and lights that they have learned to associate with food. Similarly, does the musical jingle of the neighbourhood ice cream truck tweak your hunger? Many other environmental stimuli affect food intake. We typically eat more when dining with other people than when eating alone, in part because meals take longer (de Castro, 2002). Cultural norms influence when, how, and what we eat. In countries such as Spain and Greece, people often begin dinner in the late evening (say, around 9:00 p.m.), by which time most North Americans have long finished their supper. And although we like variety, we usually feel most comfortable selecting from among familiar foods and often have difficulty “getting past” our squeamish thoughts about unfamiliar dishes. 15/11/13 10:39 AM Final PDF to printer Motivation and Emotion Obesity The heaviest known man and woman in recorded history, both Americans, weighed 635 kilograms and 545 kilograms at their respective peaks in 1978 and 1987 (Guinness Book, 2000). (After hospitalization and dieting, the man lost 418 kilograms over 16 months, and the woman lost 417 kilograms over seven years.) Health Canada guidelines suggest that a body mass index (BMI, the ratio of weight to height—kg/m2) between 25 and 29.9 is considered overweight, and a BMI over 30 is considered obese. According to recent statistics, more than half of adult Canadians (52.5 percent) are either overweight or obese, with 19.8 percent of men and 16.8 percent of women classified as obese (Statistics Canada, 2013). Among Canadian children, almost 20 percent are overweight and 8 percent are obese. Statistics Canada reported a 500 percent increase in childhood obesity between 1980 and 2004. Not only does obesity pose a health risk, but it can also expose the individual to stereotypes and prejudice (Teachman et al., 2003). Obesity is often blamed on a lack of willpower, a weak character, or emotional disturbances, but research does not consistently find such psychological differences between obese and nonobese people (Faith et al., 2002). Some scientists hypothesize that eating is an attempt to cope with stress (Wallis & Hetherington, 2004) or that obese people react more strongly than non-obese people to food cues, such as the appearance or taste of food (Stice et al., 2008). But again, evidence that these factors cause obesity is mixed (Greeno & Wing, 1994). 1998). However, although heredity affects our susceptibility to obesity, so does the environment. Genes have not changed much in recent decades, but obesity rates in Canada and the United States have increased significantly. According to experts such as James Hill and John Peters (1998), the culprits are • an abundance of inexpensive, tasty, high-fat foods available almost everywhere; • a cultural emphasis on “getting the best value,” which contributes to the “supersizing” of menu items; and • technological advances that decrease the need for daily physical activity and encourage a sedentary lifestyle. The Pima Indians of Arizona provide a striking example of how genes and environment interact to produce obesity. Despite the fact that the Pimas are genetically predisposed to obesity and diabetes, both conditions were rare among tribe members before the 20th century (Savage & Bennett, 1992). Their native diet and way of life prevented their genetic predisposition from expressing itself. But, particularly among Pimas born after World War II, obesity rates increased dramatically as they adopted a Westernized diet and sedentary lifestyle (Price et al., 1993; Esparza et al., 2000). Today, they have one of the highest rates of obesity (and diabetes) in the world. In contrast, Pimas living in northwest Mexico, who still eat a more traditional diet and perform more physical labour, have an obesity rate much lower than that of their Arizonan counterparts (Ravussin et al., 1994). Genes and Environment Dieting and Weight Loss Do you know people who seem to gain weight easily and other envied souls who eat even more food without adding weight? Data from over 25 000 pairs of twins and 50 000 other biological and adoptive family members point to heredity as one source of such differences. Heredity influences our basal metabolic rate and tendency to store energy as either fat or lean tissue (Bouchard et al., 1990). Overall, genetic factors appear to account for about 40 to 70 percent of the variation in body mass among women and men (Maes et al., 1997; Comuzzie & Allison, 1998). Identical twins reared apart are about as similar in body mass as identical twins reared together, and adopted children resemble their biological parents more closely than their adoptive parents (Stunkard et al., 1990). More than 200 genes have been identified as possible contributors to human obesity, and in most cases, it is the combined effect of a subset of genes—rather than “single-gene” variations—that produces an increased risk (Comuzzie & Allison, Unfortunately, being fat primes people to stay fat, in part by altering body chemistry and energy expenditure (Logue, 1991). For example, obese people generally have higher levels of insulin (a hormone secreted by the pancreas) than people of normal weight, which increases the conversion of glucose into fat. Substantial weight gain also makes it harder to exercise vigorously, and dieting slows basal metabolism because the body responds to food deprivation with decreased energy expenditure. Along with a genetic predisposition to obesity, these factors cause many obese people to maintain excess weight with fewer calories than people who are gaining the same weight for the first time. In contrast to earlier reports, however, there is no consistent evidence that the body’s energy-saving metabolic slowdown becomes more pronounced with each weight loss attempt (Brownell & Rodin, 1994, National Task Force, 1994). Thus, whether repeated “yo-yo dieting” makes it more difficult to lose weight is debatable. pas77416_ch11_380-428.indd 393 393 12. What evidence suggests a genetic role in obesity? How does obesity among the Pima Indians illustrate a gene–environment interaction? 13. Why is it especially hard for obese people to lose weight? Are diets doomed to fail? 15/11/13 10:39 AM Final PDF to printer 394 CHAPTER ELEVEN Applications THE BATTLE TO CONTROL EATING AND WEIGHT Many people, especially high school and university students, are concerned about their weight. Many adolescent females with average and even below-average body fat diet (Kenardy et al., 2001). Our dissatisfaction with our bodies begins at an alarmingly young age. One study found that almost 30 percent of 10- to 14-year-old girls were trying to lose weight and look thinner (McVey et al., 2004). Our body size and shape, or, more accurately, our perception of our body size and shape forms an important part of our self-image. How we perceive our own body and how closely that matches our ideal is an important issue for many (l