Mechanisms of Motivation

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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

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Drives as States of the Brain

• The hub of many central drive systems lies in the
  hypothalamus

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Hunger Drive

• Two areas of the hypothalamus, the lateral and
  ventromedial areas, play a central role in the
  hunger drive

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Lateral Area

• Electrical lesions to tract of axons connecting
  brainstem, hypothalamus and basal ganglia cause a
  loss of all goal-directed behavior
• Stimulation causes drives in response to
  available incentives

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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

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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

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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

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Effects of Culture and Habits on Body Weight

• Settling point - cluster of genetic and
  environmental factors that cause a persons
  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

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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