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Unit VIII: Motivation & Emotion Module 38 Hunger Motivation Hunger: Physiological Factors 38-1 The Physiology of Hunger 38-1 • Stomach contractions (pangs) send signals to the brain making us aware of our hunger. • But, research has shown that hunger persists without stomach pangs: Tsang (1938) removed rat stomachs, connected the esophagus to the small intestines, and the rats still felt hungry (and ate food). Body Chemistry & the Brain • Levels of glucose in the blood are monitored by receptors (neurons) in the stomach, liver, and intestines. • They send signals to the hypothalamus in the brain. 38-1 Hypothalamic Centers 38-1 The lateral hypothalamus (LH) brings on hunger. Destroy the LH, and the animal has no interest in eating. The ventromedial hypothalamus (VMH) depresses hunger (makes you feel full). Destroy the VMH, and the animal eats excessively. Hunger: Psychological Factors 38-2 The Psychology of Hunger • Memory plays an important role in hunger. • Due to difficulties with retention, amnesia patients eat frequently if given. • This suggests that part of knowing when to eat is our memory of our last meal. 38-2 Taste Preference: Biology & Culture 38-2 Body chemistry and environmental factors influence not only when we feel hunger but what we feel hungry for! Whale blubber! Roasted guinea pig! Situational Influences on Eating We eat more when eating with others. 38-2 When given a large serving utensils or a large bowl/plate, we take more food. When offered a supersized portion, we put away more calories. Obesity & Weight Control 38-3 Obesity 38-3 • Obesity is a disorder characterized by being excessively overweight. • Obesity increases the risk for health issues like cardiovascular diseases, diabetes, hypertension, arthritis, and back problems. Obesity Rates Around the World, 2010 The Genetic Factor 38-3 Studies reveal that body weight has a genetic basis • Identical twins have closely similar weights, even when reared apart. • Given an obese parent, boys are 3x more likely, and girls 6x more likely to be obese than those with normal-weight parents. • Adoptive siblings’ body weights are uncorrelated; people’s weights resemble those of their biological parents and siblings. Activity Levels 38-3 • Lack of exercise is a major contributor to obesity. • Just watching TV for two hours resulted in a 23% increase of weight when other factors were controlled. Food Consumption 38-3 Over the past 40 years, average weight gain has increased. Health professionals are pleading with US citizens to limit their food intake.