Motivation

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Motivation
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Coordination of the Systems

• Systems are complementary.
• Both are active to some extent at the same time
  not alternating.
• What happens during anger?
• Sympathetic arousal increases blood pressure.
• Medulla detects that arousal and activates the
  parasympathetic to keep blood pressure within
  normal limits.
• Hypertension occurs with deficient feedback.

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Diffuse Modulatory Systems

• A small set of diffuse modulatory neurons arise
  from the brain stem.
• Each neuron has an axon that can influence more
  than 100,000 postsynaptic neurons spread widely
  across the brain.
• Their synapses release neurotransmitter into the
  extracellular fluid, not into a confined synaptic
  cleft.

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Origins of Diffuse Neurons

• Origins vary depending on the neurotransmitter
  involved
• NE system locus coeruleus (waking, arousal,
  attention, memory, anxiety, pain, mood).
• 5-HT serotonin system raphe nuclei
  (wakefulness, mood, emotional behavior).
• DA system substantia nigra ventral tegmentum
  (reward).
• ACh system basal forebrain (unknown)

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Effects of Drugs

• Many abused drugs act directly on the modulatory
  systems.
• Hallucinogens such as LSD agonist for
  serotonin, decreasing activity of raphe nuclei.
• Stimulants (cocaine, amphetamine) affect DA and
  NE systems, causing increased alertness,
  self-confidence, euphoria.
• Mimic effects of sympathetic ANS activation.

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Drug Effects (Cont.)

• Stimulants block catecholamine reuptake and
  stimulate release of DA (dopamine), intensifying
  effects of DA and NE.
• This causes the stimulant effect.
• Because cocaine and amphetamine affect the reward
  systems, drug-seeking behaviors are reinforced
  leading to addiction or psychological dependence.

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What is Motivation?

• That which gives energy and direction to
  behavior.
• The driving force for behavior.
• Motivation is necessary for behavior but does not
  guarantee it.
• How we choose among competing goals is not well
  understood.
• Survival-related behavior is best understood.

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Motivated Behavior

• Hypothalamic regulation has three components
• Stimulation of the pituitary to release hormones
  into the bloodstream.
• Neural signals to the sympathetic and
  parasympathetic ANS.
• Somatic-motor response (behavior) to remedy the
  deficiency.
• The psychological experience is drive

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Maintaining an Energy Balance

• Eating food produces glycogens and triglycerides
  (stored as fat) which are broken down to provide
  energy for cell metabolism.
• Glucose is used by neurons, but not fatty acids
  and ketones (used by all other cells).
• Without adequate glucose, a person will lose
  consciousness and quickly die.
• Storage of glucose keeps this from happening.

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Setpoint Hypothesis of Eating

• Adiposity (fat storage) may be a regulator of
  eating behavior.
• The brain directs metabolic processes to maintain
  its fat store.
• Insulin signals the state of fat stores to the
  brain.
• Adiposity affects insulin secretion.
• Lean people are more sensitive to insulin so more
  carbohydrate is used and does not become fat.

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Appetite Control

• Starvation intake of energy consistently fails
  to meet the bodys needs.
• Adiposity (fat) intake consistently exceeds
  need
• Motivation to eat arises from a complex interplay
  of physiological mechanisms.
• Leptin levels act on the brain via peptides to
  inhibit or stimulate eating behavior and adjust
  metabolic activity.

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Short-Term Regulation

• The leptin-governed drive to eat is inhibited by
  satiety signals that occur during eating.
• Gastric distension how full the stomach feels
  is signaled by mechanosensory receptors.
• Intestines release CCK in response to
  stimulation, which inhibits appetite and releases
  insulin.
• Insulin acts like leptin to regulate feeding.

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Satiety Factors

• Stretch receptors signal fullness to prevent
  overfilling of the stomach.
• Digestive hormones secreted in the gut signal
  satiety.
• Manipulation of these hormones can change eating
  behaviors and weight in mice.

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Psychological Factors

• Learned associations with time and place.
• Socialization and rituals associated with food
  (e.g., eating at a party).
• People eat more when in social situations.
• Preferences and taste

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Dopamine Stimulates Cravings

• Originally, eating was thought to result in
  pleasure (release of dopamine in pleasure centers
  of brain).
• However, dopamine-depleted rats behave as if
  eating is pleasurable but show decreased
  motivation to seek food.
• Stimulation of dopamine pathways in hypothalamus
  appears to produce cravings, not pleasure.

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Serotonin Links Food to Mood

• Serotonin levels increase as the result of
  eating, resulting in mood elevation.
• Derived from tryptophan which comes from
  carbohydrates.
• Drugs that elevate serotonin are appetite
  suppressants.
• Abnormalities in serotonin may contribute to
  eating disorders accompanied by depression.

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Eating Disorders

• Anorexia Nervosa deliberate starvation due to
  psychological factors.
• Insufficient body weight
• Distorted body image, food obsession
• Anorexics have normal appetite
• Bulimia Nervosa food binging followed by
  purging with laxatives or vomiting.
• Normal body weight, typically

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Obesity

• Based on height and weight, a body mass index
  above 30 (above 25 is overweight).
• http//www.caloriecontrol.org/bmi.html
• Causes
• Different metabolic rate
• Larger adipocytes
• More vulnerable to food cues, finicky
• Recidivism after dieting 90 in all forms of
  treatment.

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Thirst

• Two physiological signals stimulate drinking
  behavior
• Decrease in blood volume
• Increase in the concentration of dissolved
  substances in the blood.
• Vasopressin acts on the kidneys to increase water
  retention and inhibit urine production.
• Lack of vasopressin results in diabetes insipidus.

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Temperature Regulation

• Two controls
• Sensors from skin
• Blood temperature (at hypothalamus)
• Heat-gain mechanisms increase blood temperature
  (goose bumps).
• Heat-loss mechanisms decrease it (shunt blood to
  skin, perspiration).

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Purpose of Fever

• Occurs when immune response causes heat-gain
  mechanisms to increase body temperature.
• Elevated temperature
• Activates antibody-producing cells
• Increases the rate at which white blood cells
  move to sites of infection.
• Directly affect some viruses but not all.