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• 1. Understanding of the subject matter/topic of
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• 3. The ability to clearly communicate ideas.
• 4. The ability to use APA style.

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SET POINTS VERSUS POSITIVE INCENTIVES WHAT,
WHEN AND HOW MUCH WE EAT

• Outline
• 1. Digestion and Energy Flow
• 2. Set-Point Theories v. Positive-Incentive
  Theories of Hunger and Eating
• a. Set-point Theories
• b. Positive-Incentive Theories
• 3. Factors That Determine What, When and How Much
  We Eat
• a. What We Eat
• b. When We Eat
• c. How Much We Eat
• 4. Human Obesity
• a. Why Do Only Some People Become Obese?
• b. Physiological Factors in Obesity
• 5. Anorexia Nervosa

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Digestion Energy Flow

• The primary purpose of eating is to supply the
  body with the energy that it needs to survive
• Energy is available in three forms
• (1) lipids (fats)
• (2) amino acids (broken down from proteins)
• (3) glucose (simple sugar byproducts of
  carbohydrates)
• Energy can be stored as fat, glycogen, and
  protein
• Energy is usually stored in the form of fat
• One gram of fat can contain twice as much energy
  as glycogen
• Glycogen attracts water

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Rat with a VMH lesion
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Physiology of hunger

• What is it that causes hunger? Is it the pangs
  of an empty stomach?
• A. L. Washburn working with Walter Cannon
  intentionally swallowed a balloon.
• The balloon was inflated and measured stomach
  contractions.
• Washburn pressed a button whenever he felt
  hungry.
• His stomach was contracting at these moments

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Motivation and HungerWashburn showed that
stomach contractions (transmitted by the balloon)
accompany our feelings of hunger (indicated by a
key press) Cannon, 1929
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Signals from stomach?

• Stomach does release peptide hormones
• One well studied peptide hormone is ghrelin
• In lab animals blood levels of ghrelin
• Increase with fasting
• Decrease after a meal
• In humans
• injection of ghrelin increases eating
• Also can increase thoughts of food
• Elicited vivid images of food in some people
• blood levels increase shortly prior to a meal
• Gastric bypass decreases ghrelin secretion
• Perhaps part of the reason it is successful?

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Blood glucose levels?

• Decreases in blood glucose can stimulate hunger.
• Injecting animals with insulin
• Too much gets stored
• Inject with 2-DG
• Deprives cells of real glucose
• Both can increase eating behavior
• How is blood glucose detected?
• Some evidence there are detectors in the liver
• Injecting 2-DG into the blood supply of the liver
  can increase eating
• Also in the brain
• Inject 5-TG (similar to 2-DG) into hindbrain and
  medulla can increase eating.

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Seems there are multiple systems involved in the
control of hunger

• Animals that dont produce ghrelin (knock out
  mice) eat normally
• Cutting off nerve signals from liver have little
  effect on day to day eating
• Lesions of medulla dont lead to long-term
  disturbances in eating

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Anorexia Nervosa

• About 2.5 of North American student population
• Mostly female
• 10 to 20 times more likely.

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Physical signs and symptoms of anorexia include

• Extreme weight loss
• Thin appearance
• Abnormal blood counts
• Fatigue
• Insomnia
• Dizziness or fainting
• A bluish discoloration of the fingers
• Hair that thins, breaks or falls out
• Soft, downy hair covering the body
• Absence of menstruation
• Constipation
• Dry skin
• Intolerance of cold
• Irregular heart rhythms
• Low blood pressure
• Dehydration
• Osteoporosis
• Swelling of arms or legs

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• Emotional and behavioral anorexia symptoms
• Refusal to eat
• Denial of hunger
• Afraid of gaining weight
• Lying about how much food has been eaten
• Excessive exercise
• Flat mood (lack of emotion)
• Social withdrawal
• Irritability
• Preoccupation with food
• Reduced interest in sex
• Depressed mood
• Possible use of laxatives, diet aids or herbal
  products

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Anorexia Nervosa

• Anxiety
• 80-90 of anorexics report anxiety problems prior
  to onset of the disease
• May be a genetic component
• Heritability estimate 50
• Evidence for estrogen/testosterone effects
• Onset after the start of puberty estrogen may
  promote the disease
• If male twin less likely to get anorexia
  testosterone affects prenatal organization of the
  brain
• Thus testosterone produced by male twin may
  protect against anorexia
• Female/female high
• Female/male next
• Male/female next
• Male/male lowest

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• Some evidence dont experience rewards like
  everyone else
• Sugar water didnt rate it as enjoyable as
  control group
• When playing a gambling game
• Hidden number (1-10) greater or less than 5?
• 2 correct
• - 1 incorrect
• Control group excited when correct
  disappointed when incorrect
• Previous anorexia less responsive.
• Also reward pathway in the brain was less
  activated
• fMRI

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• Women respond differently to hunger than men do
• Highshool students s allowed to each as much as
  they want from a buffet
• Baseline
• Later brought back after fasting for 24 hours.
• Males ate faster and more than they did before
• Females ate slower and less than they did before

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• Perhaps some of the symptoms of anorexia are
  symptoms of starvation
• Keys study
• 1950s
• Men volunteered to decrease eating by half
• Lost 25 of body weight
• Became preoccupied with food
• Collect recipes
• Food hording
• Erratic mood
• Withdrawn
• Lost interest in sex
• Depressed
• When allowed to eat they would dawdle over food
• Take 2 hours to eat what previously would take
  minutes
• After starvation was over some complained about
  body image
• Sign of Anorexia?

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Positive incentive model of Anorexia Nervosa

• Normally starvation increases the positive
  incentive qualities of food.
• So what is going on?

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Positive incentive model of Anorexia Nervosa

• Eatingor its consequencescan be very aversive
  to people who have been starved.
• they become nauseous, which leads them to avoid
  the foods that they have eaten.

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Positive incentive model of Anorexia Nervosa

• Conditioned aversions develop to just about any
  foods and anorexics simply stop eating.
• Treatment according to positive incentive model?
• limit them to small meals
• infusions of nutrients
• until they recover enough to avoid the aversive
  consequences of eating a meal.