1. Chapter 16
Motivation

2. Introduction
Types of behavior
Unconscious reflexes and Voluntary Movements
Motivation
Driving force on behavior
Analogy– ionic driving force dependent upon many factors
Probability and direction of behavior
Vary with the driving force needed to perform the behavior

3. The Hypothalamus, Homeostasis, And Motivated Behavior
Maintains the internal environment within a narrow physiological range
Role of Hypothalamus
Regulates homeostasis
Three components of neuronal response
Humoral response
Visceromotor response
Somatic motor response

4. The Hypothalamus, Homeostasis, And Motivated Behavior (Cont’d)
Example of motivated behaviors
Response when body is cold
Body shivers, blood shunted away from the body surface, urine production inhibited, body fat reserves - mobilized
Lateral hypothalamus
Initiates motivation to actively seek or generate warmth - Homeostasis

5. The Long-term Regulation of Feeding Behavior
Energy Balance
Prandial state - Anabolism: Energy storage as glycogen and triglycerides
Postabsorptive state - Catabolism: Breaking down complex macromolecules

6. The Long-term Regulation of Feeding Behavior

7. Hormonal and Hypothalamic Regulation of Body Fat and Feeding
Body Fat and Food Consumption
Lipostatic hypothesis
Parabiosis: e.g., Siamese twins
Leptin
Regulates body mass
Decreases appetite
Increases energy expenditure
Leptin depletion
Incites adaptive responses
to fight starvation

8. Hormonal and Hypothalamic Regulation of Body Fat and Feeding
The Hypothalamus and Feeding
Anorexia: lateral hypothalamic syndrome
Obesity: ventromedial hypothalamic syndrome
Both related to leptin signaling

9. Hormonal and Hypothalamic Regulation of Body Fat and Feeding
The Hypothalamus and Feeding
Hypothalamic nuclei important for the control of feeding

10. Hormonal and Hypothalamic Regulation of Body Fat and Feeding
Response to Elevated Leptin Levels
Activation of arcuate neurons that release αMSH and CART peptides
Anorectic peptides- diminish appetite
Activation of arcuate neurons that release αMSH and CART peptides (Cont’d)
Project to regions that orchestrate coordinated response of humoral, visceromotor, and somatic responses
Paraventricular nucleus (humoral response)
Intermediolateral gray matter of spinal cord
Lateral hypothalamus

11. Hormonal and Hypothalamic Regulation of Body Fat and Feeding
Response to Elevated Leptin Levels

12. Hormonal and Hypothalamic Regulation of Body Fat and Feeding
Response to Decreased Leptin Levels
Activation of arcuate neurons that release NPY and AgRP
Effects on energy balance: Opposite to the effects of αMSH and CART
Orexigenic peptides– increase appetite
NPY and AgRP inhibit secretion of TSH and ACTH
Activate parasympathetic division of ANS
Stimulate feeding behavior

13. Hormonal and Hypothalamic Regulation of Body Fat and Feeding
Response to Decreased Leptin Levels

14. Hormonal and Hypothalamic Regulation of Body Fat and Feeding
The Control of Feeding by Lateral Hypothalamic Peptides
LH neurons stimulating feeding behavior contain:
Melanin-concentrating hormone (MCH)
Orexin

15. Harry Harlow – in 1967 received the National Medal of Science for his work on general human and child psychology. His work examined motivation in monkeys.

21. The Short-Term Regulation of Feeding Behavior
Model for short-term regulation of feeding
3 phases: Cephalic; Gastric; Substrate

22. The Short-Term Regulation of Feeding Behavior
Model for short-term regulation of feeding
Cephalic: Hunger
Ghrelin released when stomach is empty
Activates NPY- and AgRP-containing neurons in arcuate nucleus

23. The Short-Term Regulation of Feeding Behavior
Model for short-term regulation of feeding
Gastric: Feeling full
Gastric distension signals brain via vagus
Works synergistically with CCK released in intestines in response to certain foods
Insulin also released by B cells of the pancreas - important in anabolism

24. The Short-Term Regulation of Feeding Behavior
Model for short-term regulation of feeding
Changes in blood insulin levels before, during, and after a meal
Highest during “substrate” phase

25. Why Do We Eat?
Reinforcement and Reward
Liking: Hedonic
Wanting: Drive reduction
Electrical self-stimulation: Experiments to identify sites of reinforcement
Effective sites for self-stimulation:
Trajectory of dopaminergic axons in the ventral tegmental area projecting to the forebrain
Drugs that block dopamine receptors: Reduce self-stimulation

26. Why Do We Eat?
Mesocorticolimbic dopamine system

27. Why Do We Eat?
The Role of Dopamine in Motivation
Old belief: Dopamine projection served hedonic reward
New understanding
Dopamine-depleted animals “like” food but “do not want” food
Lack motivation to seek food, but enjoy it when available
Stimulation of the dopamine axons
Craving for food without increasing the hedonic impact

28. Why Do We Eat?
Changes in hypothalamic serotonin levels
Low:Postabsorptive period
Rise: In anticipation of food
Spike: During meals
Mood elevation - Rise in blood tryptophan and brain serotonin

29. Why Do We Eat?
The Role of Dopamine in Motivation
Serotonin, Food, and Mood (Cont’d)
Drugs that elevate serotonin levels
Example: Dexfenfluramine (Redux)
Disorders: Anorexia nervosa; Bulimia nervosa both often accompanied by depression
Treatment
Antidepressant drugs—elevate brain serotonin levels
Example: Fluoxetine (“Prozac”)

30. Other Motivated Behaviors
Drinking: Pathway triggering osmotic thirst
Hypertonicity: Increased concentration of dissolved substances in blood (salt)

31. Other Motivated Behaviors
Drinking: Vasopressin - Antidiuretic hormone or ADH
Acts on kidneys to increase water retention
Inhibit urine production
Diabetes insipidus - loss of vasopressin