10 basic drives and motives

... Discussion-Homosexuality and Social Development Other Basic Motives 308 Thirst Avoidance of Pain Maternal Behavior Curiosity and Stimulus-Seeking Current Status of Motivational Concepts 313 10 BASIC DRIVES AND MOTIVES. .. balance between the female hormones (estrogen and pro- 310 CHAPTER 10 / BASIC DRIVES AND MOTIVES gesterone) and prolactin from the anterior pituitary gland, which is involved in the production of... Figure 10- 10 Sensory Deprivation Experiment Cardboard cuffs and a translucent blindfold reduce stimulation 312 CHAPTER 10, BASIC DRIVES AND MOTIVES soon became bored, restless, irritable, and emotionally

Part Five MOTIVATION

AND EMOTION

10 / Basic Drives and Motives • 1 1 / Motivation and Emotion

Instincts Needs and Drives Incentives Critical Discussion-Ethology and Species-Specific Behavior

Hunger 288

Regulatory Centers in the Hypothalamus Short-Term Control of Food Intake Long-Term Control of Food Intake

Obesity 293 Factors That Influence Eating

Exercise and Eating Behavior Modification and Weight Control Critical Discussion-Are Some People Programmed to Be Fat?

Sex 298 Biological Basis of Sexual Behavior

Role of Experience Critical Discussion-Sexual Fantasies

Homosexuality Transsexualism Critical Discussion-Homosexuality and Social Development

Other Basic Motives 308

Thirst Avoidance of Pain Maternal Behavior Curiosity and Stimulus-Seeking

Current Status of Motivational Concepts 313

BASIC DRIVES

AND MOTIVES

When we ask, "What motivates people to risk their lives to save another or

to work long hours to achieve a particular goal?" we usually mean, "Why

do people behave the way they do?" As it is popularly used, the term

"mo-tivation" refers to the cause or why of behavior Used in this sense, motivation

would cover all of psychology Psychologists , however, confine the concept of

motivation to those factors that energize behavior and give it direction A

mo-tivated organism will engage in an activity more vigorously and more efficiently

than an unmotivated one In addition to energizing the organism, motivation

tends to direct behavior (a hungry person is motivated to seek food and to eat;

a thirsty person , to drink; a person in pain, to escape the painful stimulus).

Although many psychologists would concur with this definition of

tivation, it is still a controversial concept Some psychologists feel that

mo-tivation accounts only for the energizing aspects of behavior and that other

mechanisms (namely, learning and cognition ) account for the direction of

be-havior Some even argue that a concept of motivation is unnecessary (Bolles,

1975) To help clarify this controversy , we will briefly describe how the concept

of motivation developed and the various forms it has assumed since the

begin-ning of this century Then we will consider the basic biological needs that

humans share with lower organisms In the next chapter, we will discuss more

complex human motives.

THEORETICAL APPROACHES

TO MOTIVATION

The term "motivation" was not used until the beginning of the twentieth

century For hundreds of years, the predominant view of philosophers and

theologians was that people were rational beings with intellects who freely

chose goals and decided on courses of action Reason determined what a

person did; a concept of motivation was unnecessary A person was free to 283

284 CHAPTER 10 / BASIC DRIVES AND MOTIVES

choose, and choices were good or bad, depending on the individual's ligence and education It was assumed that the good choice, if known, wouldautomatically be selected According to this conception of the human being,

intel-called rationalism, a person is largely responsible for his or her own behavior.

Philosophers did not break away from the concept of rationalism until theseventeenth and eighteenth centuries At this point, some philosophers began

to take a more mechanistic view of behavior and suggested that actions arose

from internal or external forces over which people had no control In theseventeenth century, Hobbes held that no matter what reasons people gave fortheir conduct, the underlying causes of all behavior were the tendencies to seek

pleasure and to avoid pain This doctrine of hedonism still plays a major role in

some motivation theories

Instincts

The extreme of the mechanistic view is the theory of instincts An instinct is an

innate biological force that predisposes the organism to act in a certain wayunder appropriate circumstances Animal behavior had long been attributed toinstincts; animals were considered to have no soul or intellect and to be unable

to reason Darwin's theory that there was no sharp distinction betweeen mans and animals opened the door for the use of instinct theory to explainhuman behavior The strongest advocate of instinct theory, the psychologist

hu-William McDougall, maintained that all our thoughts and behavior were the

result of inherited instincts-compelling sources of conduct that could be

modified by learning and experience In his book Social Psychology (1908),

Mc-Dougall mentioned the following instincts:

acquisitionconstructioncuriosityflightgregariousness

pugnacityreproductionrepulsionself-abasementself-assertion

McDougall later expanded his list to 18 instincts, including some that related tospecific bodily needs By modifying and combining these instincts, he at-tempted to explain all human behavior

Instinct theory was diametrically opposed to a rationalistic view of humanbeings Instead of choosing goals and actions, a person was at the mercy ofinnate forces, which determined-or motivated-behavior

Psychoanalytic theory also attributed behavior to powerful innate forces.Freud believed that two basic but unconscious energies were powerful mo-

tivational forces in determining behavior-the life instincts expressed in sexual behavior and the death instincts underlying aggressive acts (see Chapter 11).

Both psychoanalytic theory and instinct theory influenced the change from arationalistic conception of human beings to a motivational view, which sawbehavior as the result of unconscious, irrational forces within the individual

Needs and drives

It soon became clear that a great number of instincts would have to be lated to account for the subtleties of human behavior Such behaviors as rivalry,secretiveness, modesty, cleanliness, imitation, cruelty, sociability, and jealousy

postu-THEORETICAL APPROACHES TO MOTIVATION

were identified as instincts Eventually, almost any imaginable behavior could

be termed an instinct However, labeling a particular action "instinctive" did

not really explain much about it except to imply that it might be inherited To

say that a man fought because he had a pugnacious instinct did not provide

much more than a description of the behavior It did not explain the behavior

In addition, anthropologists noted that some instincts were not found in

all cultures Pugnacity, for example, was not typical of all primitive societies;

in some societies, people had no need to fight

During the 1920s, instinct theory was replaced by the concept of drives A

drive is an aroused state that results from some biological need, such as a need

for food, water, sex, or avoidance of pain This aroused condition motivates the

organism to remedy the need For example, lack of food produces certain

chemical changes in the blood that in turn create a drive state The organism

attempts to reduce the drive by doing something (in this case, finding food) to

satisfy the need This is a drive-reduction theory of motivation.

Sometimes the terms "need" and "drive" are used interchangeably, but

more often "need" refers to the physiological state of tissue deprivation and

"drive" refers to the psychological consequences of a need Need and drive are

parallel but not identical Drive does not necessarily become stronger as need

becomes stronger A starved organism may be so weakened by its need for

food that drive (the motivation to find food) is weakened

HOMEOSTASIS AND DRIVE THEORY Basic to the drive concept is the

prin-ciple of homeostasis-the body's tendency to maintain a constant internal

envi-ronment The healthy individual maintains a body temperature within the

range of a few degrees Slight deviations from normal temperature activate

mechanisms that restore the normal condition Exposure to cold constricts

blood vessels on the body's surface to retain the warmth of the blood, and

shivering produces heat In warm weather, peripheral blood vessels dilate to

permit heat to escape, and perspiration has a cooling effect

Numerous biological states must be maintained within fairly narrow limits,

restore balance

State

monitor

Figure 10-I

Motivational Control System

The state monitor continuously measures the internal condition of the organism Whenever the comparator notes a difference between the state monitor and some optimal level, it emits an error signal The error signal acti- vates cognitive processes that select behaviors designed to restore the balance between the state monitor and the optimal state These behaviors link the organism to its environ- ment, producing feedback to the system that restores the imbalance between the optimal state and the current state The system is organized to maintain the state monitor at a level nearly equal to the optimal level at all times.

The response patterns animals display

in the care of their young provide a clear

example of the type of behavior that has

been called "instinctive." Building

nests, removing the amniotic sac so the

newborn can breathe, feeding the

young, and retrieving them when they

stray from the nest are all complex

be-havior patterns that animals exhibit

without the opportunity to learn A

squirrel performs maternal duties in the

same manner as all other mothers of its

species, whether it is caring for the first

litter or the fifth

Interest in instinctive behavior,

which declined during the early part of

this century, has been revived by a

group of European psychologists and

zoologists who call themselves

ethol-ogists These scientists study animals in

their natural environment rather than in

the laboratory, where the artificial

sur-roundings often prevent behavior

pat-terns from appearing in natural form

(Lorenz, 1981)

Ethologists prefer the term

species-specific behavior to the more controversial

term "instinct." They study behavior

that is specific to a certain species and

that appears in the same form in all

members of the species

Imprinting-a concept introduced

by ethologists-refers to a type of early

learning that forms the basis for the

young animal's attachment to its

par-ents A newly hatched duckling that has

been incubated artificially without the

presence of a mother duck will follow a

CHAPTER 10/BASIC DRIVES AND MOTIVES

CRITICAL DISCUSSION

human being, a wooden decoy, or most any other moving object that it firstsees after birth Following a woodendecoy for as little as 10 minutes isenough to "imprint" the duckling onthe decoy; the duckling will remain at-tached to this object, follow it even un-der adverse circumstances, and prefer it

al-to a live duck Imprinting occurs mostreadily 14 hours after hatching but canhappen any time during the first twodays of life After this point, imprinting

is difficult, probably because the ling has acquired a fear of strangeobjects

duck-Imprinting has been found in anumber of species-including dogs,sheep, and guinea pigs-but it is mostclearly developed in birds that are able

to walk or swim immediately after birth

An innate mechanism ensures that theyoung will follow and remain close totheir mothers (normally the first movingobject they see) rather than wander offinto a perilous world

Studies of mallard ducks haveidentified the stimuli that are importantfor imprinting in birds and indicate thatthe phenomenon begins even beforebirth Ducklings begin to make sounds

in their eggs a week before they breakthrough the shells Mallard mothers re-spond to these sounds with cluckingsignals, which increase in frequencyabout the time the ducklings hatch

Auditory stimuli before and after ing, together with tactile stimulation inthe nest after birth, thoroughly imprint

hatch-Imprinting in ducklings

The newly hatched duckling follows the

model duck around a circular track The duckling soon becomes imprinted on the model and will follow it in preference to

a live duck of its own species The more effort the duckling has to exert to follow the model (such as climbing a hurdle) the stron- ger the imprinting ( After Hess, 1958)

the ducklings on the female mallard inthe nest An unhatched duckling thathears a recording of a human voice say-ing "Come, come, come" instead of itsmother's voice will imprint on a decoythat utters "Come, come, come" as eas-ily as it will imprint on a decoy that

including the concentration of blood sugar, the levels of oxygen and carbondioxide in the blood, and water balance in the cells Various body mechanismsoperate to keep these conditions stable Sensors in the body detect changesfrom the optimal level and activate mechanisms that correct the imbalance Theprinciple is the same as a heater thermostat, which turns the heat on when thetemperature falls below a certain level and off when the temperature rises.Hunger and thirst can be viewed as homeostatic mechanisms because theyinitiate behavior that restores the balance of certain substances in the blood.Within the framework of homeostasis, a need is any physiological departure

THEORETICAL APPROACHES TO MOTIVATION

Ethology and Species-Specific Behavior

utters normal mallard clucks Ducklings

that have been exposed to a mallard

fe-male's call prior to hatching are more

likely to imprint on decoys that utter

mallard clucks (Hess, 1972)

Ethologists have also developed the

concept of a releaser-a particular

envi-ronmental stimulus that sets off a

species-specific behavior In some

young seagulls, a red or yellow spot on

the mother's beak "releases" a pecking

response, which causes the mother to

regurgitate the food that the infant will

Austrian ethologist Konrad Lorenz

demon-strates how young ducklings follow him

in-stead of their mother because he was the first

moving object they saw after they were

hatched.

eat Varying the color and shape of thespot on cardboard models and observ-ing whether the young gull pecks at the

"beak" make it possible to determinethe characteristics of the releaser towhich the bird responds

Owl-like figures initiate mobbingbehavior (a kind of feigned attack) bybirds for which the owl is a natural en-emy The swollen abdomen of the fe-male stickleback fish initiates courtshipbehavior by the male The bowing andcooing behavior of the male ring dovereleases the entire sequence of re-productive behavior in the female (nest-building, laying and incubating theeggs) and is responsible for the hor-monal changes that accompany theseactivities (Lehrman, 1964)

The higher an animal is on the lutionary scale, the fewer species-specific behaviors it exhibits and themore learning determines the actions ittakes to satisfy its needs But even hu-mans have some built-in behavior pat-terns, including the rooting reflex of thehuman infant Touching a nipple to thecheek of a newborn elicits head turningand simultaneous mouth opening If themouth contacts the nipple, it closes onthe nipple and begins to suck This be-havior pattern is automatic and can oc-cur even when the infant is sleeping Atabout six months, the rooting reflex issuperseded by voluntary behavior; thetypical 6-month-old sees the nipple,reaches for it, and tries to bring it to his

evo-or her mouth

from the optimal state; its psychological counterpart is drive When the iological imbalance is restored, drive is reduced and the motivated activityceases Many physiological imbalances are corrected automatically The pan-creas releases sugar stored in the liver to maintain the proper balance of sugar

phys-in the blood But when automatic mechanisms can no longer maphys-intaphys-in a anced state, the organism becomes aroused (drive is activated) and is motivated

bal-to resbal-tore the balance A person who experiences the sympbal-toms of low sugar level seeks food Figure 10-1 (see page 285) schematically represents thetype of control system that regulates such homeostatic mechanisms

blood-288 CHAPTER 10! BASIC DRIVES AND MOTIVES

Psychologists have broadened the principle of homeostasis to includepsychological as well as physiological imbalances Any psychological imbal-ance will also motivate behavior designed to restore equilibrium Thus, ananxious or fearful person will be motivated to do something to reduce thetension

Incentives

During the 1950s, psychologists began to question the drive-reduction theory of

motivation as an explanation of all types of behavior It became apparent that

the organism was not pushed into activity solely by internal drives; external stimuli, called incentives, also played an important part in arousing behavior.

Motivation could be better understood as an interaction between stimuli in theenvironment and a particular physiological state of the organism

Delicious-looking pastries in a bakery window may arouse the hungerdrive of a person who is not hungry In this case, the incentive (fresh pastries)activates rather than reduces hunger A satiated animal will eat again if it seesanother animal eating In these instances, the motivation is not an internaldrive but an external stimulus

Furthermore, some evidence contradicted the homeostatic concept of drive

as the organism's attempt to reduce tension and return to a quiescent state.Human beings often seek tension-arousing experiences, such as roller-coasterrides, car racing, white-water canoeing, or horror movies These activitiesincrease tension rather than reduce it

More recent approaches to a theory of motivation have focused on the role

of incentives-motivating objects or conditions in the environment The

or-ganism approaches positive incentives and avoids negative incentives To a thirsty

animal, a positive incentive would be water; to a sexually aroused animal,

a mate An object or situation that has caused pain would be a negativeincentive An incentive arouses the organism and directs behavior toward oraway from it

The dual function of incentives can be demonstrated experimentally Ahungry rat will run through a maze to a goal box that it knows contains food;the positive incentive directs behavior If it is given a small pellet of food at thestart of the maze, the rat runs toward the goal box even faster; the incentivealso arouses behavior As in drive theory, arousal is an important aspect ofmotivation; here, however, arousal is evoked by an external incentive ratherthan by conditions of deprivation

Now that we have considered various concepts of motivation, we willexamine some specific motivational systems All the concepts mentioned hereare useful in explaining some aspects of behavior Even instinct theory is beingrevitalized in the study of certain behavior patterns-although from a differentviewpoint than at the beginning of this century

HUNGER

Eating is influenced by social customs Scene

is the Great Hall of the People, Peking, on

May Day eve.

Because it has been the subject of intensive research, hunger will be the firsttopic considered Hunger can be a powerful motivator; people who have sub-sisted on semistarvation diets report that much of their thinking and dreamingconcerns food and eating The body needs an adequate supply of nutrients to

HUNGER 289

function efficiently Depletion of these nutrients activates homeostatic

mech-anisms to release food stored in the body; for example, the liver releases stored

sugar into the bloodstream Replenishment from body stores enables a person

to continue to function even after missing several meals When the body stores

are diminished to a certain point, however, the automatic homeostatic

mech-anisms are no longer adequate and the entire organism becomes mobilized to

seek food

What internal signals tell the brain that the body's supply of nutrients is

low and it must find food? The feelings most people describe as hunger-an

empty or aching sensation in the stomach sometimes accompanied by a feeling

of weakness-give us some clues, but there are other signals

External stimuli can influence feelings of hunger and eating behavior

After a full meal, you may still want to eat a delicious dessert In this case, your

cue for hunger is not internal The odor or sight of food can arouse hunger even

when there is no physiological need

Habits and social customs also influence eating behavior You are

accus-tomed to eating at certain times of the day and may suddenly feel hungry when

you notice that it is noon You may consume more when you have dinner with

friends who eat voraciously than you do when you dine alone

Eating behavior is influenced by a number of physiological,

environ-mental, and social variables Here, we will examine the physiological

mech-anisms that regulate food intake; we will consider the environmental and social

factors that influence eating behavior when we discuss obesity in the next

section

Regulatory centers in the hypothalamus

Regulation of food intake is so crucial to the survival of the organism that

nature has provided several homeostatic controls If one or more sensory

signals associated with eating is eliminated (smell, taste, or sensory

informa-tion from the stomach), the organism is still able to regulate food intake The

control systems that regulate eating behavior are located in a region of the brain

Hunger can be aroused by external influences.

CHAPTER 10 / BASIC DRIVES AND MOTIVES

called the hypothalamus-a small collection of cell nuclei at the base of the brain

(see Figure 2-7) that is directly linked with other parts of the brain and with thepituitary gland The hypothalamus also contains more blood vessels than anyother area of the brain, so that it is readily influenced by the chemical state ofthe blood

The development of precise instruments for exploring the brain has abled researchers to specify two areas of the hypothalamus that influence food

en-intake The lateral hypothalamus (LH) initiates eating (it is a "start" or "feeding center"); the ventromedial hypothalamus (VMH) inhibits eating (it is a "stop" or

"satiety center") One way to study the function of a specific brain area is tostimulate the spot with a weak electric current Stimulation of the LH causes

a satiated animal to eat Stimulation of the VMH inhibits eating; a weak currentslows the animal's feeding behavior, and a stronger current will stop it entirely.Another way to study the function of a brain area is to destroy cells andnerve fibers in the region and observe the animal's behavior when the area nolonger exerts control When tissue in the LH is destroyed, the animal refuses

100

9013 -J00 "''\ to eat or drink and will die unless it is fed and watered artificially Damage to

D^GR

tcaPacir

tissue in the VMH produces overeating and obesity in every speciesonn '.' investigated-from rat and chicken to monkey and human (see Figure 10-2)

Peo le with tumors or in uries in thep j reg on oi f th he ypoth la amus may overeatFigure 10-2

Hypothalamic Overeating (a condition called hyperphagia) and become obese.

Lesions in the ventromedial hypothalamus Studies of this type demonstrate that the VMH area (satiety center) and the

(VMH) caused this rat to overeat and gain LH area (feeding center) act in opposite ways to regulate food intake

More-more than three times its normal weight over, two kinds of control systems appear to be integrated in the

hypo-thalamus One short-term control system is responsive to the immediate tive needs of the organism and tells the brain when to start and stop a meal

nutri-A second, long-term control system maintains a stable body weight over anextended time period regardless of how much the organism may eat in any onemeal

Short-term control of food intake

Investigators have identified three variables that influence hypothalamic trol of immediate appetite: blood-sugar level, stomach fullness, and body tem-perature A low sugar or glucose level in the blood makes the organism feelweak and hungry Injections of insulin (which lower the blood-sugar level)increase food intake; injections of glucose (which raise the blood-sugar level)inhibit eating

con-Studies indicate that the hypothalamus contains "glucoreceptors"-cellssensitive to the rate at which glucose passes through them Glucoreceptors inthe VMH and the LH respond differently to the glucose level in the blood.Microelectrodes have been implanted in the hypothalamus of dogs and cats torecord neural activity in the VMH and LH before and after injections of glucose

or insulin After glucose injections, cells in the VMH (satiety center) becamemore active, whereas cells in the LH (feeding center) decreased in activity Thereverse results occurred after insulin injections Cells monitored in other parts

of the brain showed no changes (Anand, Sharma, and Dua, 1964; Oomura,1975)

But digestion is a slow process The organism stops eating long before thefood it has consumed can be transformed into enough blood sugar to make up

a deficit in the bloodstream A more immediate signal-a full stomach-lets thebrain know that the food is on its way If food is injected directly into the

HUNGER 291

stomach of a hungry animal (without passing through the mouth and throat),

it eats much less than it would otherwise If food is removed from a satiatedanimal's stomach (via a tube), the animal will eat enough to compensate forthe food loss Experiments suggest that cells in the VMH respond to thedistension of the stomach and inhibit further eating (Deutsch, Young, andKalogeris, 1978)

An empty stomach produces the periodic contractions of muscles in thestomach wall that we identify as "hunger pangs." This increased movement ofthe stomach wall activates cells in the LH Therefore, an empty stomach signalsthe LH to initiate eating; a full stomach signals the VMH to stop eating

A third short-term control mechanism of food intake is body temperature.Most animals and humans eat less in a warm environment than they do in acold environment Cooling the brain has a similar effect on food intake Thenature of these "thermoreceptors" in the brain is not clear, but evidence showsthat the LH responds to decreased brain temperature and the VMH responds

to increased brain temperature

Thus, the LH responds to low blood-sugar level, increased motility of thestomach walls, and lowered brain temperature by initiating eating; conversely,the VMH responds to high blood-sugar level, stomach distension, and in-creased brain temperature by stopping eating But these short-term mech-anisms are subject to a long-term mechanism that attempts to stabilize bodyweight over time

Long-term control of food intake

Most wild animals maintain about the same level of weight throughout theirlifetimes, even though food may be plentiful one week and scarce the next It

is more difficult for human beings to maintain a constant weight because theireating behavior is strongly influenced by emotional and social factors Even so,most people remain at approximately the same weight level from year to year

In addition to its short-term controls of food intake, the hypothalamus appears

to regulate a delicate system that ensures that the organism's weight remainsstable over time

We noted that a rat with damage to the VMH overeats and becomes obese.Originally, this increase in appetite was attributed to the destruction of part ofthe short-term control system But once the rat reaches a certain level of obesity(usually two or three times its normal weight), it no longer overeats It reducesits food intake to slightly more than a normal level and maintains its new obeseweight If the animal's diet is restricted, it will decrease to its original normalweight; if it is allowed to eat freely again, it will overeat until it returns to itsobese state It appears that damage to the VMH disturbs the animal's long-termweight control system so that weight is regulated at a higher level

If obese rats are force-fed until they become "super obese," they reducetheir food intake until their weight returns to its "normal obese" level (seeFigure 10-3) Some correlate of body weight must act on the VMH to influencefood intake Autopsies of animals with VMH lesions indicate that theinfluential factor may be the amount of free fatty acids in the bloodstream

In contrast, rats with lesions in the LH refuse all food and water for sometime after the operation and will die unless they are artificially fed After severalweeks, most of these rats will resume eating and drinking on their own, butthey stabilize at a lower weight level, just as VMH-damaged rats stabilize at anobese level (Mitchel and Keesey, 1974) Again, this behavior indicates im-

Figure 10-3

Effects of Forced Feeding and Starvation

on Body Weight of Rat with VMH Lesions

Following VMH lesioning , the rat overeats

and gains weight until it stabilizes at a new,

obese level Forced feeding or starvation

al-ters the weight level only temporarily; the rat

returns to its stabilized level (After Hoebel

Body Weight and

the Lateral Hypothalamus

Prior to LH lesioning , one group of rats was

starved while the other group was allowed to

feed freely Following surgery, the starved

animals increased their food intake and

gained weight and the freely fed group lost

weight Both groups stabilized at the same

weight level ( After Powley and Keesey, 1970)

CHAPTER 10/BASIC DRIVES AND MOTIVES

pairment of a long-term weight control system rather than simple decreasedappetite Rats that are starved prior to LH lesioning do not refuse to eat afterthe operation In fact, many of them overeat, but only until their weight reaches

a new level-lower than their normal weight but higher than their starved,preoperational weight (see Figure 10-4)

These findings indicate that the VMH and the LH have reciprocal effects

on the "set point" for body weight Damage to the VMH raises the set point;

damage to the LH lowers it If both areas are lesioned carefully so that an

equivalent amount of tissue is destroyed in each area, the animals do notovereat or undereat but maintain their presurgery weight levels (Keesey andPowley, 1975)

Although the hypothalamus plays a crucial role in the control of eatingbehavior, other brain regions are also involved, including the limbic sytem andcertain nuclei in the brain stem where sensory neurons carrying informationabout taste and smell converge Thus, the hypothalamus may be more accu-rately described as a critical link between the higher and lower brain areas that

regulate eating behavior rather than as the area containing feeding and satiety

OBESITY

Obesity is a major health problem Each year, people spend millions of dollars

on special diets, drugs, and other treatments to lose weight Most people are

not very successful in losing weight; those who succeed in shedding pounds

almost invariably regain them These problems have stimulated much research

on the origin and control of obesity

A popular view is that obesity stems from unresolved emotional problems

Fat people were starved for love as children and food symbolizes "mother's

love"; or overeating is a substitute for other satisfactions lacking in the

individ-ual's life Although such explanations may be appropriate in some cases, the

backgrounds of most overweight people are no more psychologically disturbed

than those of normal-weight individuals Fat people are often unhappy, but

their distress is primarily a result rather than a cause of their obesity In

a society where thinness is equated with beauty, overweight people tend to

be embarrassed by their appearance and ashamed of their supposed lack of

control

Thus far, research has failed to isolate a personality type that characterizes

obese people Rather than focusing on the individual's personality or emotional

background, current studies of obesity are considering the situational factors

that lead to overeating What cues prompt a person to eat? How do obese

people differ in their responses to these cues?

Factors that influence eating

RESPONSIVENESS TO FOOD CUES The sight, aroma, and taste of food affect

how much we eat and when we eat Research suggests that obese individuals

may be more responsive to these food cues than people of normal weight One

study examined the effects of taste on the eating behavior of underweight and

overweight subjects The subjects were allowed to eat as much vanilla ice cream

as they wanted and then were asked to rate its quality Some subjects were

given a creamy, expensive vanilla ice cream; the others, a cheap vanilla ice

cream with quinine added to make it slightly bitter Figure 10-5 plots the

subjects' ratings against the amount of ice cream eaten Overweight subjects

ate much more ice cream when they rated it "excellent" than they did when

they rated it "bad." The ice-cream consumption of underweight subjects was

less affected by taste; in fact, they ate somewhat more than the overweight

subjects when the ice cream was rated "bad." Taste therefore appears to be

particularly important to overweight subjects

Obese individuals also seem to be highly responsive to the sight of food

When bright lights are focused on a dish of cashew nuts, overweight

individ-uals eat twice as many nuts as they do when the lights are dimmed People of

normal weight eat about the same number of nuts regardless of how well they

can see them (Ross, 1974) Even listening to a mouth-watering description of

food prompts overweight individuals to eat much more than normal-weight

individuals under the same conditions (Rodin, 1981)

Evidence from these and other studies indicates that the eating behavior

of obese individuals is highly responsive to stimuli associated with food But

is this greater responsivity a consequence rather than a cause of being

over-weight? The question does not have a simple answer There is substantial

good

Evaluation of ice cream

Figure 10-5

Taste and Obesity

The effects of food quality on the amount

eaten by overweight and underweight jects The subjects rated the quality of ice cream and could eat as much as they desired (After Nisbett , 1968b)

sub-294 CHAPTER 10 / BASIC DRIVES AND MOTIVES

evidence, however, suggesting that responsivity plays a role in obesity; someindividuals appear to be unusually sensitive to external cues that elicit eating(Rodin, 1981) Increased responsivity may also be influenced by an inheritedcomponent that can be identified at birth In one study, infants who had two

overweight parents showed a greater preference for sugar solutions and were

generally more responsive to food cues than infants who had two weight parents Such findings suggest that the offspring of overweight parents

normal-are more likely to become obese than the offspring of normal-weight pnormal-arents

(Milstein, 1980)

EMOTIONAL AROUSAL Overweight individuals often report that they tend

to eat more when they are tense or anxious, and experiments suggest that this

is true Obese subjects eat more in a high-anxiety situation than in a anxiety situation; normal-weight subjects eat more in the low-anxiety situation(McKenna, 1972)

low-Any kind of emotional arousal seems to increase food intake in some obese

people In one study, overweight and normal-weight subjects saw four filmsduring four different sessions Three of the films aroused various emotions:one was distressing; one, amusing; one, sexually arousing The fourth film was

a boring travelogue After viewing the films, the subjects were asked to tasteand evaluate different kinds of crackers The obese subjects ate significantlymore crackers after viewing any of the arousing films than they did after seeingthe travelogue Normal-weight individuals ate the same amount of crackersregardless of which film they had seen (White, 1977)

CONSCIOUS RESTRAINT OF EATING The studies we have examined suggestthat obese people tend to be more responsive than normal-weight individuals

to the taste and sight of food and other sensations aroused by food They arealso more apt to eat when emotionally aroused But one variable we have not

considered is that overweight individuals are more likely to be dieting than thin

or normal-weight individuals, and some of their responsiveness to externalcues may stem from this fact People who are hungry all the time might beexpected to pay more attention to food

To better understand the effects of dieting, a questionnaire was developedthat asked about diet and weight history (for example, "How often are youdieting?"; "What is the maximum amount of weight that you have ever lost in

a month?") as well as concern with food and eating (for example, "Do you eatsensibly before others, yet make up for it when alone?"; "Do you have feelings

of guilt after overeating?")

The results of the questionnaire showed that almost everyone-whetherthin, plump, or fat-could be classified into one of two categories: people whoconsciously restrained their eating and people who did not In addition, nomatter what their actual weight, "restrained eaters" behaved more like obeseindividuals than "unrestrained eaters." For example, when normal-weightsubjects were placed in an anxiety-producing situation, those categorized asrestrained tended to increase their food intake (like the obese) whereas theunrestrained eaters tended to eat less (Herman and Polivy, 1980)

The control of the dieter is tenuous, however, and is vulnerable to externalinfluences, as anyone who has repeatedly broken a diet knows Dieting mayactually increase the chances of overeating In one study, restrained and un-restrained eaters (both of normal weight) were required to drink two milk-shakes, one milkshake, or none; they then sampled several flavors of ice creamand were encouraged to eat as much of the ice cream as they wanted The moremilkshakes the unrestrained eaters were required to drink, the less ice cream

they consumed later In contrast, the restrained eaters ate more ice cream after

they had been preloaded with two milkshakes than they did after drinking one

milkshake or none Apparently, once the restrained eaters had overeaten

through preloading, their control broke down completely (Herman and Mack,

1975)

A similar experiment with thin, normal, and obese subjects revealed that

dieting was a more critical factor in predicting eating behavior than weight The

three weight groups did not differ significantly in the amount of ice cream they

ate after being preloaded with two milkshakes or none But when the data were

analyzed for restrained versus unrestrained eaters regardless of weight, the

differences were highly significant (see Figure 10-6) Nondieters (unrestrained

subjects) ate much less after two milkshakes than after none, whereas dieters

(restrained subjects) ate more

In these experiments, the forced loading of milkshakes makes the subjects

lose control of their eating behavior Once restrained eaters lose control, they

eat much more than unrestrained eaters do Restrained eaters are continuously

trying to inhibit their food intake; when they lose control (when their attempts

to inhibit eating fail), motivation collapses and they begin overeating Loss of

inhibition is a key factor in influencing obesity, as illustrated by an experiment

involving alcohol, which is well-known for its inhibition-releasing effects The

study indicated that alcohol increased food intake among restrained eaters but

not among unrestrained eaters (Polivy and Herman, 1976) Anxiety and

de-pression also tend to weaken self-control And research indicates that

re-strained eaters eat more when they are anxious or depressed, whereas

un-restrained eaters eat less (Herman and Polivy, 1980)

Exercise and eating

The body's level of energy expenditure is critical to weight control Energy

expenditure depends on two factors: (1) general activity level and exercise; and

(2) the basal metabolic rate, or the energy required to maintain minimal body

functions Of the two, basal metabolism accounts for about two thirds of a

normal-weight person's energy expenditure For the overweight individual,

however, energy expenditure is inhibited because the metabolic rate is lower

in fat tissue than in lean tisssue Thus, the individual's basal metabolic rate

decreases as lean tissue is replaced by fat Metabolic rate also decreases during

periods of food deprivation; consequently, when an individual starts to diet,

the basal metabolic rate decreases Both of these factors work against the efforts

of an overweight person to reduce

Physical activity accounts for only about one third of a normal individual's

energy expenditure, but it plays a more critical role in the amount of energy

expended by an overweight person Exercise, of course, burns off calories; the

more an individual exercises, the more calories are burned off But exercise also

indirectly affects basal metabolism If a person is sedentary, the metabolic

mechanism fails to operate properly and produces a lower basal metabolic rate

(Garrow, 1978) Lack of exercise sets up a vicious cycle: obesity makes physical

exercise more difficult and less enjoyable, and inactivity results in fewer

cal-ories being burned off (directly through exercise and indirectly through a

reduced basal metabolic rate) Thus, exercise is critical in weight loss-not only

because it burns calories but also because it helps to regulate normal metabolic

functioning (Thompson and others, 1982)

Our discussion indicates that obesity results from the interplay of genetic,

metabolic, psychological, and environmental events The importance of each of

295

-145E130

Figure 10-6

Restrained and Unrestrained Eaters

Subjects concerned with dieting consumed more ice cream after previously over- indulging in milkshakes than subjects uncon- cerned about controlling their food intake, regardless of body weight (After Hibscher and Herman, 1977)

296 CHAPTER 10/ BASIC DRIVES AND MOTIVES

these factors varies from individual to individual Despite the complexity of theproblem, weight control is possible in most cases To diet successfully, over-weight individuals must recognize that they tend to be unusually responsive

to environmental cues that elicit eating and that anxiety or emotionally vocative situations tend to cause them to overeat Being aware of these factorsand guarding against their influence are important steps in gaining control ofone's weight Further, the role of exercise in weight control is more significantthan folklore would suggest Exercise burns calories and, equally important,ensures proper functioning of the metabolic process

pro-Behavior modification and weight control

To successfully control weight, the individual must become aware of the factorsthat lead to overeating and must try to establish a new set of eating and exercisehabits A study comparing methods for treating obesity illustrates this conclu-sion For six months, obese individuals followed one of three treatment regi-mens: (1) behavior modification of eating and exercise habits, (2) drug therapyusing an appetite suppressant (fenfluramine) and (3) a combination of behaviormodification and drug therapy Subjects in all three treatment groups weregiven information on exercise and extensive nutritional counseling, including

a 1,000-1,200 calorie diet There were two control groups One control groupconsisted of subjects waiting to take part in the study, who received no treat-ment of any kind The other control group consisted of subjects who saw aphysician for traditional office treatment of weight problems, which involvedthe use of fenfluramine, a reducing diet, information on diet, advice, andencouragement

Behavior modification, received by two of the three treatment groups,involved a program like the one described in Chapter 16 (see page 505) The

OBESITY 297

CRITICAL DISCUSSION

Are Some People Programmed to Be Fat?

Obesity runs in families; fat parents

tend to have fat children Except for a

few cases that are clearly the result of

hormonal disorders, no biological cause

has been determined that predisposes

people to obesity However, the eating

patterns of obese individuals and rats

with VMH lesions are remarkably

simi-lar Both eat more at a given meal and

eat more rapidly than normal

organ-isms, and both are highly responsive to

food tastes These similarities have led

to the speculation that the

hypo-thalamus of obese individuals sets a

higher than normal baseline for fat

tissue-that these individuals are

"bio-logically programmed to be fat"

(Nis-bett, 1972)

Body fat is stored in special fat cells

called adipocytes Obese individuals

dif-fer from non-obese individuals both in

the size and in the number of these fat

cells In one sample, obese subjects

were found to have three times as many

fat cells as normal subjects (Knittle and

Hirsch, 1968) This is an important

finding because the number of fat cells

in an individual is set at an early age and

remains relatively fixed throughout life

Overeating increases the size of a

per-son's fat cells but not the number;

star-vation decreases the size of a person's

fat cells but not the number After

weight loss, formerly obese individuals

have the same number of fat cells,

which will be filled up again if they start

overeating Individuals who have a

large number of fat cells have a higher

baseline of body fat than individuals who

have fewer fat cells

Heredity and early nutrition both

probably play roles in determining an

individual's number of fat cells, but the

causal relationship is not clear Some

re-searchers believe that a person's fat-cell

count is genetically fixed at birth Others

think that the number of fat cells is termined by nutrition during the earlymonths of life; overfeeding an infantmay stimulate the development of fatcells In any event, evidence indicatesthat the individual's baseline of body fat

de-is fairly well establde-ished by 2 years ofage (Knittle, 1975) The hypothalamiccenters maintain this baseline by regu-lating food intake to maintain fat stores

at a certain set point or level

We have seen that rats with damage

to the VMH (satiety center) regulatetheir weight at a new, higher level andthat rats with lesions in the LH (feedingcenter) regulate their weight at a new,lower level It is possible, then, that theset points for obese and non-obese indi-viduals of the same height and bonestructure are different If this is true,obesity for some individuals is their

"normal" weight, which their thalamus tries to maintain Attempts atweight reduction by such individualswould hold them below their biologi-cally determined set point in a state ofchronic deprivation; they would feelhungry all the time-just like a thin per-son on a starvation diet would feel

hypo-Stunkard (1982) has theorized thatappetite-suppressant drugs like fen-fluramine act primarily to lower the setpoint and only secondarily to suppressappetite His theory explains thefindings on drug therapy for obesity dis-cussed in the text-namely, the rapidregaining of body weight following thewithdrawal of fenfluramine in contrast

to the relative stability of weight lossachieved with behavior modification

The drug lowered the set point of tients, thereby facilitating weight loss;

pa-discontinuation of the drug caused theset point to return to its pretreatmentlevel The resulting biological pressure

to gain weight until the higher set point

is reached produced a greater weightgain in drug-therapy subjects than insubjects who lost weight without the aid

of drugs These ideas cast doubt onthe effectiveness of appetite-suppres-sant medication in the treatment ofobesity

The set-point theory is intriguing but

controversial For example, according tothe theory, increased sensitivity to foodcues is a consequence rather than acause of obesity Extremely overweightpeople have eaten so much that they are

at their set point But many less obeseindividuals remain below their set point

by dieting, and this deprivation creases their receptivity to stimuli asso-ciated with food Thus, proponents ofthis theory argue that the longer obeseindividuals diet (the more weight theylose), the more sensitive they are to foodcues But experiments do not seem toconfirm this prediction Sensitivity tostimuli associated with food appears toremain relatively constant regardless ofthe amount of weight loss a person ex-periences (Rodin, 1981)

in-The set-point concept has ated considerable interest and research,but there are too many contrary findingsfor it to serve as a general theory of obe-sity However, it may account for cer-tain types of problems-particularly theindividual who was moderately over-weight as a child and remains mod-erately overweight throughout life Ahigher than normal set point may be onereason for overconsumption, but thereare undoubtedly others Most over-weight people, unlike the VMH-damaged rats, do not suddenly becomeobese Their fat accumulates over a pe-riod of months or years-a kind of

gener-"creeping obesity" that results fromgradually consuming more calories thanthe body expends in energy

Table 10-1

Weight Loss Following

Different Treatments

Weight loss in pounds at the end of six

months of treatment and at a follow-up one

year later Subjects in the two control groups

were not available for the one-year followup.

(After Craighead, Stunkard , and O' Brien,

1981)

CHAPTER 10! BASIC DRIVES AND MOTIVES

WEIGHT LOSS AFTER TREATMENT

WEIGHT LOSS AFTER ONE YEAR

Physician office visits 13.2

subjects were taught to keep a daily record of their eating habits, to becomeaware of situations that prompted them to overeat, to change the stimulusconditions associated with their overeating, to reward themselves for appropri-ate eating behavior, and to develop a suitable exercise regimen

Table 10-1 presents the results of the study As might be expected, thesubjects in all three treatment groups lost more weight than the subjects in thetwo control groups At the end of treatment, the group combining behaviormodification with drug therapy lost the most weight (33.7 pounds) The drug-therapy-only group did almost as well (31.9 pounds), but the behavior-modification-only group lost significantly less (24 pounds) However, duringthe year after treatment was discontinued, a striking reversal developed Thebehavior-modification-only group regained far less weight than the other twogroups; these subjects maintained an average weight loss of 19.8 pounds by theend of year, whereas the weight losses for the drug-therapy-only group and thecombined treatment group were only 13.8 and 10.1 pounds, respectively.What caused this reversal? An increased sense of "self-efficacy" may havebeen a factor Subjects who received the behavior-modification-only treatmentcould attribute their weight loss to their own efforts, thereby strengthening

their resolve to continue controlling their weight after the treatment was over.

Subjects who received an appetite suppressant, on the other hand, probablyattributed their weight loss to the medication and did not develop a sense ofself-control; when the drug was withdrawn, releasing biological pressures toregain weight, their sense of self-efficacy was not strong enough to prevent

them from returning to their old eating habits The drug also decreased feelings

of hunger, and subjects in the drug-therapy-only group and the combinedtreatment group may not have been prepared to cope with the increase inhunger that occurred when the medication was stopped

This study demonstrates that short-term weight loss can be accomplished

in a variety of ways But the ability to keep weight off permanently depends

on establishing self-control over eating habits and therefore over the totalnumber of calories consumed

SEX

Sex, another powerful motivator, differs in many respects from hunger Unlikefood, sex is not vital to the survival of the organism, but it is essential to thesurvival of the species Eating reduces tissue deficits With sex, however, there

is no deficit; sexual behavior uses energy rather than restores it