Transcript Mechanisms of Motivation

Mechanisms of Motivation
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Motivation and Incentives
 Motivation - factors within and outside an
organism that cause it to behave a certain
way at a certain time
 Motivational state or drive - an internal
condition, which can change over time, that
orients an individual to a specific set of goals
(e.g., hunger, thirst, sex, curiosity)
 Incentives - goals or reinforcers in the
external environment (e.g., good grades,
food, a mate)
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Drives as Tissue Needs
 Homeostasis - the constancy of internal
conditions that the body must actively
maintain
 Drives may be an upset in homeostasis,
inducing behavior to correct the imbalance
 Animals do behave in accordance with their
tissue needs (e.g., increasing or decreasing
caloric intake, drive for salt)
 However, homeostasis cannot explain all
drives
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Types of Drives
Regulatory drives - helps preserve
homeostasis (e.g., hunger, thirst,
oxygen)
Nonregulatory drives - serve other
purposes (e.g., sex, achievement)
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Drives as
States of the Brain
Central state theory of drives different drives correspond to neural
activity in different sets of neurons in
the brain
Central drive system - set of neurons
in which activity constitutes a drive
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Drives as
States of the Brain
Techniques
for studying
central drive
systems
include
lesions and
stimulation
Connecting Socket
Electrode
Brain
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Drives as
States of the Brain
Cerebral cortex
 The hub of
many central
drive systems
lies in the
hypothalamus
Hypotahlamus
Portion of
limbic system
Pituitary
gland
Brainstem
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Hunger Drive
 Two areas of the
hypothalamus,
the lateral and
ventromedial
areas, play a
central role in
the hunger drive
Hypothalamus
Hypothalamus
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Lateral Area
 Electrical lesions to
tract of axons
connecting
brainstem,
Hypothalamus
hypothalamus and
basal ganglia cause
a loss of all goaldirected behavior
 Stimulation causes
drives in response to
available incentives
Hypothalamus
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Lateral Area
 However,
chemical lesions
to specific cell
bodies reduce
hunger drive, but
do not abolish it most other drives
appear normal
Hypothalamus
Hypothalamus
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Ventromedial Area
 Lesions alter
digestive and
metabolic
processes
 Food is converted
into fat rather than
energy molecules,
causing animal to
eat much more
than normal and
gain weight
Hypothalamus
Hypothalamus
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Hunger Drive
 Other stimuli that act on the brain to
increase or decrease hunger include
satiety signals from the stomach
signals indicating the amount of food
molecules in the blood
leptin, a hormone indicating the amount of
fat in the body
the appetizer effect
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Research on Weight
Regulation and Dieting
 No consistent personality trait differences
found between obese and non-obese people
(e.g., willpower, anxiety)
 Dieters and obese are more likely to eat in
response to stress than non-dieters
 Family environment of little importance in
determining body weight - genetics plays a
large role
 Number of fat-storage cells is a major
determinant of body weight
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Research on Weight
Regulation and Dieting
 Fat cells are determined by genetics and food intake
 They increase with weight gain, but merely shrink
with weight loss - may stimulate hunger
 Weight loss causes a decline in basal metabolism
Fat cells
Normal
diet
High-fat
diet
Return to
normal diet
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Effects of Culture and
Habits on Body Weight
 Settling point - cluster of genetic and
environmental factors that cause a person’s
weight to settle within a given range
 Weight can be affected by factors like diet,
exercise, and daily habits (e.g., stairs instead
of elevator)
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Sex Drive
 Increased production
of testosterone and
estrogen at puberty
is responsible for
physical
differentiation
 Increased secretion
of DHEA, primary
adrenal sex hormone,
is responsible for
sexual feelings
First sexual
attraction in
both sexes
Final maturation
of testes in males
Final maturation
of ovaries in females
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Male Sex Drive
 Testosterone
maintains sex drive
in adult males
castration decreases
drive
testosterone
injections or
implantation to
medial preoptic area
restores drive
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Female Sex Drive
 Estrous cycle controls
drive in nonhuman
mammals
 removal of ovaries
abolishes drive, while
hormone injections
restore it
 Also, lesions to
ventromedial area
abolish drive, while
injection or
implantation restores
drive
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Female Sex Drive
Female monkeys and apes depend less
on hormones for sexual behavior
Human female sex drive may not be
consistently affected by hormone
cycle at all
ovarian hormones play small role
adrenal hormones like DHEA and
testosterone play larger role
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Early Effects of Testosterone
 Presence of testosterone during critical
period will cause rudimentary genitals of
fetus to develop into male structures
 Testosterone acts in brain to promote
development of neural systems for male sex
drive and inhibit systems for female drive
 Absence causes development of female
structures
 Stressful events experienced by pregnant
rats reduce level of prenatal testosterone
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Human Sexual Orientation
 Orientation is an early-emerging, ingrained
aspect of the self that probably does not
change
 No consistent relationship between
orientation and childhood experiences (e.g.,
parenting, abuse, sexual experience)
 Controversial findings suggest a possible
relationship among prenatal stress,
androgens, and the development of brain
systems that play a role in sexual attraction
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Reward Pathways in the
Brain
Medial forebrain bundle runs from the
midbrain through the lateral area of the
hypothalamus into the nucleus
accumbens in the basal ganglia
neurons in this tract secrete dopamine
animals will self-stimulate this pathway
euphoria-producing drugs affect the level of
dopamine in this tract
evolved to promote survival and
reproduction
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