Chapter 4: Physiological Mechanisms of Regulation

PSY 338: Motivation

Hunger Motivation: Why do we eat?

Internal Factors

External Cues

Hunger Motivation: Why do we eat?

Memory

Rozin, Dow, Moscovich & Rajaram (1998)

Procedure• Amnesic and non-amnesic participants feed full meal; offered next two meals in 30 minute intervals

Results•Amnesic participants were likely to accept and partially eat both subsequent meals; non-amnesic declined the offer

Interpretation•Memory is a major determinant of when we get hungry

What structures are doing the regulating?• Local Theories

• Peripheral organs of the body control feeding behavior and bodyweight (e.g., stomach, vagus nerve)

Local Theories

Cannon & Washburn (1912)Hunger Experiment•Washburn swallowed a balloon to record stomach contractions•Pushed button to report hunger feelings•Hunger feelings came at peak of contractions•Contractions lead to hunger, not vice-versa

What structures are doing the regulating? • Central Theories

• Specialized cells in the brain control feeding behavior and bodyweight (e.g., hypothalamus)

Short-Term Regulation

What controls eating over short periods of time? •Balance energy intake with energy expenditure

Short-Term Regulation

Center Theory•Ventromedial hypothalamus

• Satiety center; Damage caused hyperphagia

•Lateral hypothalamus• Hunger center; Damage caused

aphagia

What initiates a meal? What terminates a meal?

VMH lesioned rat is on left

Glucostatic Theory of Hunger

Blood Glucose •This is a simple sugar used by most cells in the body for energy - most food ultimately gets converted to blood glucose

Mayer (1955)•Decreasing blood glucose levels sense of hunger•Receptors in the hypothalamus detect these changes and thus regulate our eating motivations

Many limitations to this theory; receptors are not primarily responsible for short-term regulation

Long-Term Regulation of Hunger

Controls a steady bodyweight

Lipostatic Theory •Set-point view: the brain tries to maintain steady lipid (fat) levels

•Set point is the weight that your body wants to be•It is a self-regulatory system that maintains your body weight•If you starve yourself the hypothalamus activates compensatory mechanisms, your metabolism slows so that energy stores are used more sparingly and the amount of insulin that is produced increases so that more of the food that you take in remains as fat

Long-Term Regulation of Hunger

Dual-Center Theory of feeding behavior•Encompasses the set-point idea but that it’s a dual process•VMH as a "satiety center" and LH as a "Hunger center“•VMH lesion causes hyperphagia & obesity; LH lesion causes aphagia and anorexia

Nonhomeostatic Eating Behavior

What other factors affect the initiation and/or the termination of a meal? Hedonic factors must be considered as well.•Learning: anticipation of meals •Taste preferences: Pleasurable effects of food•Taste aversions: Disgust

Failure of Regulation: Eating Disorders

Anorexia Nervosa•There are physiological abnormalities that are correlated with the disorder but are these abnormalities causes or effects?

Search for causes:•Homeostatic theory encourages the search for physical deficits in homeostatic mechanisms•Non-homeostatic theory encourages the study of non-regulatory mechanisms such as learning and social influences

Anorexia NervosaSelf-starvation and severe weight loss•Usually starts as an innocent diet that went out of control•Often they come from high-achieving or over-protective families

• Restricting Type• Binge/Purging Type

Case Study: Karen Carpenter• Famous singer died of complications to anorexia (cardiac

arrest) in 1983 at the age of 32

Anorexia: Facts and Statistics

Lifetime prevalence in US: •Adults: 0.6%•15-24 year old females: 2%•Onset is in childhood

Anorexia Nervosa

Symptoms•Body dissatisfaction; body distortion•Lethargy•Irritability

•Depression

•Social withdrawal

•Obsessiveness (food)

Anorexia Nervosa

Complications

•Hypothermia may result

•Amenorrhea

•Some will die from heart failure

Anorexia Nervosa• Treatment

• Hospitalization or outpatient care may be a necessary first step• Clinical: Individual, group, and family therapy are then applied• Anti-depressants are often combined with these therapies• Nutrition Therapy can be introduced after patients have

recovered enough so that non-compliance is not a major obstacle

• Self-help group therapy is an option for those without the financial means or insurance to utilize the above options

• Prognosis• There is a good chance for improvement and hopefully recovery • However, it is a life-long process

Anorexia Nervosa TheoriesCross-Cultural Evidence•Not seen much in non-white culturesSerotonin Hypothesis•Higher levels when anorexics are at normal body weight but low levels as they reduce weightHeredity Factors•5-10% risk in first degree relatives

Holland, Sicotte, & Treasure (1988)•Twin study•Monozygotic twins: 56% concordance•Dizygotic twins: 5% concordance

Brain Structures•Limbic system structures seem primarily involved (hypothalamus, insula)

Bulimia Nervosa

Purging Type•Disorder characterized by repeated binge-purge episodes of overeating followed by vomiting or using a laxativeNonpurging Type•Fasting; excessive exercise

Bulimia: Facts and Statistics

Gender •89% are femaleAppearance•These individuals can be thin, average in weight or even overweight – so this one is more likely to go unnoticed by family or friendsOnset•ChildhoodSpecific Populations•The incidence is estimated to be 3% in the general population; but as high as 10% of college women may suffer from it

Bulimia Nervosa

Complications•Sore throat•Mouth and throat ulcers•Swollen salivary glands•Destruction of tooth enamel•Depression, obsessive-compulsive symptoms•Amenorrhea

Bulimia NervosaCalam & Waller (1998)Procedure•Longitudinal study followed 63 females from age 12 to age 19

Results•Bulimic attitudes in early teenage years were related to bulimic symptoms in early adulthood•Poor family communication also a factor

Interpretation

Good news:•Unhealthy eating attitudes and behaviors can be predicted from early teenage characteristics•Targeting prevention and early intervention programs might be developed

Bad news:•These behaviors may be in place too early•Treatment difficult

Theories of Bulimia

Sociocultural approach•The primary cause is unrealistic social norms

Clinical/psychiatric approach •The primary cause is an affective disorder

Epidemiological/risk factors approach•This approach looks at the risk factors leading to this disorder

Social contagion•The primary cause is an interaction between unrealistic social norms and affective disorder

Neurotransmitters•Serotonin Hypothesis

ObesityWeight which is 20-40% above the normal standard for a person’s height (BMI over 30)

Basal Metabolic Rate

The amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans)•BMR decreases as you age•Depriving yourself of food in hopes of losing weight also decreases your BMR, a foil to your intentions•Exercise increases BMR•Lean body mass (LBM) also decreases with age

Obesity Explanations

Adaptiveness Gone Wrong•Normal weight has approximately one month of stored energy•In obese, the storage system has continued past normal levels

Genetic predisposition•More fats cells lead to genetically programmed to carry more weight •Problem with one or more homeostatic mechanisms•High sensitivity to one or more nonhomeostatic factors

Obesity ExplanationsObesity as maintaining obesity•Hyperinsulinemia

• Insulin involved in fat storage process; increases the amount of energy stored away as fat; the more insulin, the more energy that can be stored away as fat

•Activity levels• Obese usually less active so they burn less calories• Fat tissue is metabolically less active than lean tissue

•Dieting• Weight cycling• Metabolic rate is reduced during food deprivation• New set-point may be established

Obesity ExplanationsSchacter (1971)Procedure•Normal weight and obese participants sequestered for a week•Lived in college dorms •Watches taken from participants•Clocks alteredResults•Obese more likely to be hungry than normals when clocks were around mealtimesInterpretation•The difference between obese and normal weight participants is that the obese are overly responsive to external stimuli (cues for eating)•Externality Hypothesis

The Role of Habituation in Obesity

A decrease in the magnitude of a response as the result of repeated stimulation•Organisms decrease responding to a stimulus after repeated exposures•A simple form of learning in which the organism learns something about a single stimulus•Common examples:

• Noises in your house• Traffic• Air conditioning/furnace

The Role of Habituation

Dishabituation•Habituation to a stimulus can be temporarily blocked by a novel stimulus•The novel stimulus increases the response to the original stimulus when the original is re-presented

Dishabituation

Siddle (1985)•Participants receive 15 presentations of 4-second tone•Response to tone decreases to almost nothing as the result of habituation•New stimulus (patch of red light) is presented•New response specific to light occurs•Tone is then presented again (16th time overall)•Response increases as compared to 15th presentation; dishabituation has taken place•Presenting the tone again will lead to the reappearance of habituation; response returns to previous low level

The Role of Habituation

Epstein, Temple, Bouton, & Roemmich (2009)•Many stimuli associated with eating food making habituation likely; eating that food should decrease•However, if dishabituating stimulus occurs then eating behavior is also likely to return•When we vary what we eat, habituation is less likely to occur

Obesity as Addiction

Palatability of food may be addictive•Pleasurable, rewarding part nor related to homeostatic system•Related to hedonic system that appears to promote addiction-like behaviors

Stress leads to Obesity

Animal studies demonstrate that stress can produce overeating•Seems to cause elevation of ghrelin levels and reduce levels of leptin leading to overeating, increased hunger for high fat diets, and increased body weight

Regulation of Thirst• Water constitutes 70% of the mammalian body• Water in the body must be regulated within narrow limits• The concentrations of chemicals in water determines the rate

of all chemical reactions in the body

Regulation of Thirst

Two different kinds of homeostatic thirst include:

1. Osmometric thirst – a thirst resulting from eating salty foods

2. Volmetric thirst – a thirst resulting from loss of fluids due to bleeding or sweating

Each kind of thirst motivates different kinds of behaviors

Nonhomeostatic DrinkingEating seems to be a potent stimulus for drinking; nonhomeostatic influence

Kraly (1984)•Normal drinking occurs around meals for people and animals•Lab rats: as much as 90% of daily water intake occurs near mealtime (10:00 before to 30:00 after)

Regulation of Sexual Motivation

Sex Hormones•Testosterone (males)•Estrogen (females)

Sexual Dimorphism

Refers to sexual differences between males and females•This is the result of the action of a gene found on the Y (male) chromosome•For first 6 weeks, fetal development is the same for both males and females•Then SRY male gene starts producing a protein that causes the testes to develop

Hypothalmic Regulation

Damage to hypothalamus•Hypogonadal conditions: Lack of sexual motivation

Regulation of Aggressive Motivation

Nonhomeostatic motivation •Cortex of the brain is unnecessary for the expression of anger

Cannon (1929)• Decorticate cats displayed “sham rage”• Lesions in cortex yet displays of anger accompanied by normal autonomic arousal

Limbic SystemAmygdala•Emotional control center of the brain – major influence on aggression and fear

Kluver & Bucy (1939)•Aggressive monkeys became tame after lesions in this area

Olvera (2002)•Intermittent explosive disorder has been traced to amygdala (as well as the prefrontal cortex)

Limbic System

Hypothalamus

Pleasure center may be involved in the spontaneity of aggressive behavior

Flynn et al. (1970)•Affective attack – high emotionality; can be elicited by electric stimulation of VMH•Quiet biting attack – low emotionality, predatory behavior; can be elicited by electric stimulation of LH and thalamus

Neurotransmitters

Serotonin •Low levels increase aggression

GABA•Low levels increase aggression

Opioids•Low levels increase aggression

Dopamine•High levels increase aggression

Credits

Some slides prepared with the help of the following websites:• http://pirate.shu.edu/~vigorimi/Motivation_and_Emotion/chapter4.htm• plaza.ufl.edu/laurajf/lectures/Chapter%2012.ppt• web.campbell.edu/faculty/asbury/ppt/chapter10.ppt• http://www.futuresofpalmbeach.com/anorexia-treatment/facts-

statistics/• http://www.anred.com/stats.html