Motivation and the Regulation of Internal States Motivation and Homeostasis Learning about Hunger

1. Motivation and the Regulation of Internal States Motivation and Homeostasis Learning about Hunger

2. Motivation and Homeostasis • Motivation: • means “to set in motion,” • refers to the set of factors that initiate, sustain, and direct behaviors. • Is an inferred state: hypothetical • Instinct: • complex behavior that is automatic and unlearned • occurs in all the members of a species. • Examples: migration and maternal behavior • Do humans have instincts?

3. Theories of motivation • Drive theory: • McDougall, 1924 • Theory that states the body maintains a condition of homeostasis, in which any particular system is in balance or equilibrium. • Any departure from homeostasis, such as depletion or nutrients or a drop in temperature, produces an aroused condition or drive, • This drive impels the individual to engage in appropriate action such as eating, drinking, or seeking warmth. • Incentive theory: • Bolles, 1967 • recognizes alternative sources of drive beside internal • Notes that people and animals motivated by external stimuli, not just internal needs.

4. Theories of Motivation • Arousal theory: • Fiske and Maddi (1961); • Yerkes/Dodson 1967 • people and animals behave in ways that keep them at their preferred level of arousal. • Optimal arousal and optimal performance interact

5. Control systems and Homeostasis • Control system: • System which sustains a (life) function • Has a variety of loops and functions • Uses a set point to determine optimal performance. • Negative feedback loop: • Set point: point of equilibrium for the system • Furnace and thermostat are a control system and set point • Furnace is the control system • The thermostat is set at a set point; furnace maintains house at that set point

6. Why is this so important? • Must be SOME kind of central (brain) control of regulatory behavior • Hunger • Thirst • Fear/Aggression • Sex • Some of those must be learned • E.g., favorite kind of food • Fear of clowns • When to have sex • WHAT exactly controls our starting and stopping of these behaviors? • Multiple factors • Very complex!!!!

7. temperature • Preoptic area of the hypothalamus: • The “thermostat” of the hypothalamus, • which contains separate warmth-sensitive and cold-sensitive cells. • Some of these neurons respond directly to the temperature of the blood flowing through the area. • Other neurons receive input from temperature receptors in other parts of the body, including the skin.

9. How do you know you are thirsty? • Local thirst: • Thirst is sensation arising from dry mouth • Local “sign” or cue • Data suggest dry mouth not a sufficient “cause” to induce drinking • Intracellular vs. extracellular thirst • Intracellular: losing water from cells • Extracellular: losing water volume outside of cells • Knew that volume loss = thirst, but what about intracellular hydration?

10. How do you know you are thirsty? • Gillman (1937): classic experiment on cell dehydration • Injected dogs with NaCl or Urea into bloodstream • NaCl does not penetrate cells; Urea does penetrate cells • Premise: if injected concentration of NaCl in bloodstream higher than in cells, would pull water out of cells and make you thirsty • Urea should not produce this effect • Dogs drank only with NaCl • Showed that dehyrdating cells was what was important

11. Two kinds of thirst • Osmotic thirst: • occurs when the fluid content decreases inside the cells. • blood becomes more concentrated than usual • usually because the individual has not taken in enough water to compensate for food intake. • As a result, water is drawn from the cells into the bloodstream by osmotic pressure. • Hypovolemic thirst • occurs when the blood volume drops due to a loss of extracellular water. • This can be due to sweating, vomiting, and diarrhea • Also to severe bleeding! • Double-depletion hypothesis: • Takes both osmotic and hypovolemic effects to make you drink • Suggests multiple inputs and multiple outputs

12. Signaling the brain • NST (nucleus of the solitary tract) of medulla • Receives signals of reduced blood volume in the heart • This occurs with volemia • is signaled by the vagus to the in the medulla. • OVLT: organumvasculosum lamina terminalas • Area of hypothalamus bordering third ventricle • Detects reduced water content of cells that contributes to osmotic thirst • communicates the water deficit to the median preoptic nucleus of the hypothalamus, • This results in initiation of drinking. • median preoptic area of the hypothalamus • Receives signals from NST • Initiates drinking.

14. Hormonal changes and thirst • Lowered blood volume is also detected by receptors in the kidneys, which trigger release of the hormone renin. • Renin increases production of the hormone angiotensin II. • Angiotensin II circulating in the blood stream informs the brain of the drop in blood volume. • It stimulates the SFO (subfornical organ), • a structure bordering the third ventricle • one of the areas that is unprotected by the blood-brain barrier.

15. Satiating thirst • Voluntary dehydration: • We stop drinking before water deficit is made up • Why? If we didn’t, we would literally drown our cells • Two mechanisms to control satiation • Learning: unlikely, would be dead before learned! • Underlying physiological mechanism • Inhibition of drinking • Sequence of drinking: drink-stomach-absorbed in intestines-to bloodstream-to cells • Mouth factors important cues • Stomach factors: fullness • Intestines: again, sensation of fullness • Cells: signal as get water, not when full

16. Hunger:choosing what to eat • The simplest form of dietary selection involves: • distinguishing between foods that are safe and nutritious and those that are either useless or dangerous. • Choosing appropriate food for setting • Most likely use taste to do this. • In humans, all taste experience is a result of just five taste sensations: • sour, • sweet, • bitter, • salty, • and the more recently discovered umami. • Umami is often described as “meaty” or “savory.”

17. Satiating thirst • Voluntary dehydration: • We stop drinking before water deficit is made up • Why? If we didn’t, we would literally drown our cells • Two mechanisms to control satiation • Learning: unlikely, would be dead before learned! • Underlying physiological mechanism • Inhibition of drinking • Sequence of drinking: drink-stomach-absorbed in intestines-to bloodstream-to cells • Mouth factors important cues • Stomach factors: fullness • Intestines: again, sensation of fullness • Cells: signal as get water, not when full

18. Hunger:choosing what to eat • The simplest form of dietary selection involves: • distinguishing between foods that are safe and nutritious and those that are either useless or dangerous. • Choosing appropriate food for setting • Most likely use taste to do this. • In humans, all taste experience is a result of just five taste sensations: • sour, • sweet, • bitter, • salty, • and the more recently discovered umami. • Umami is often described as “meaty” or “savory.”

19. Hunger: taste IS important • Taste receptors are located on taste buds • Taste buds found on surface of tongue • Contained in papillae • Papillae are small bumps on the tongue and elsewhere in the mouth. • Taste neurons travel through the thalamus to the insula, the primary gustatory (taste) area in the frontal lobes.

21. Hunger: A Complex Drive • Sensory-specific satiety: • the more a particular food an individual eats, the less appealing the food becomes. • Can still eat other “tastes” • Think of eating dessert after a large meal! • Sensory-specific satiety is the brain’s way of encouraging you to vary your food choices, which is necessary for a balanced diet. • Sensory-specific satiety takes place in the NST (nucleus of the solitary tract) in the medulla.

22. Obesity: reset setpoint • basalmetabolism: • the energy required to fuel the brain and other organs and to maintain body temperature • Appear to be differences in basal metabolism in obese vs. normal weight individuals • In the average sedentary adult, about 75% of daily energy expenditure goes into resting or basal metabolism • The remainder is spent about equally in physical activity and in digesting food. • In normal weight individuals- this is much lower