Introduction to Psychology

Motivation and Control of Action

Prof. Jan Lauwereyns

jan@sls.kyushu-u.ac.jp

Homeostasis

Definition – ‘Maintenance of the body’s internal environment within a narrow physiological range’

Internal environment – refers to body temperature and blood compositions

HypothalamusPrimarily involved in maintaining body temperature, fluid and energy homeostasis

Thirst• Water regulation is critical: 70% of body is water

– concentration of chemicals determines rate of reactions

– blood volume must be enough to maintain blood pressure and circulation

• Strategies for regulation– too much: excess water excreted through

urination – too little: vasopressin, anti-diuritic hormone,

constricts blood vessels to increase blood pressure and enables kidneys to reabsorb water and secrete concentrated urine

Energy Balance

Why is it important?Brain needs constant glucose supply

A few minutes glucose deprivation leads to loss of consciousness and death

Hunger

Biological needs

The drive reduction hypothesis

Think: Inclusive fitness (Darwinian processes)

Think: energy, reproduction

Approach

Avoid

Biological needs

Several hours have passed since last meal

Increased drive (hunger)

Increased exploratory activity

Find food, eat it

Drive is reduced (reinforcement)

The drive reduction hypothesis

Biological needs

Several hours have passed since last meal

Find food, eat it

Drive is reduced (reinforcement)

The drive reduction hypothesis

Increased drive (hunger)

Increased exploratory activity

Biological needs

Several hours have passed since last meal

Find food, eat it

Drive is reduced (reinforcement)

The drive reduction hypothesis

Increased drive (hunger)

Increased exploratory activity

Wanting

Liking

When do you start (wanting) a meal?

- Cultural and social factors (habit, copy)

- Physiological factors (hunger)

Eating: Physiological factors

• Fuel for cells:– Glucose (brain)– Fatty acids (rest of the body)

• Glucose in a meal some used for fuel some

converted into glycogen

• The glucostatic hypothesis of hunger

Neurons in the hypothalamus

• Lateral hypothalamus: – Neurons signal hunger (“glucostats”)– When damaged, no hunger, won’t eat, will

starve

Glucose, Insulin and Glucagon• Glucose

– much of digested food enters bloodstream as glucose, primary energy source for cells in body and brain

– remains constant because liver converts stored nutrients to glucose

• Amount of glucose actually available to cells depends on two hormones from pancreas – insulin helps glucose enter cells, decreasing

amount in bloodstream – glucagon stimulates liver to convert glycogen to

glucose, increasing amount in bloodstream

Neurons in the hypothalamus

• Lateral hypothalamus: – Neurons signal hunger (“glucostats”)– When damaged, no hunger, won’t eat, will

starve

• Ventromedial hypothalamus:– Neurons signal satiation– When damaged, never enough, will keep

eating, grow very obese

After a meal insulin levels rise and glucose enters cells, appetite decreases – as glucose levels fall, the pancreas

releases glucagon and less insulin– less glucose for immediate fuel, blood

levels rise and hunger returns

Untreated diabetics eat much but lose weight. Because of their low insulin levels, the glucose in their blood cannot enter the cells, either to be stored or to be used. Consequently, glucose is excreted in their urine, leaving the cells to starve.

• When do we eat more than we need?– when we are with other people– in the evening– on weekends– if food is low-fat– when it tastes good– alcoholic beverages add calories

• Disorders– Anorexia nervosa, bulimia– Hormonal conditions (e.g., leptin)