Brain and Motivational States:Resting metabolic state, Individual differences

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Neurological Basis of Behavior (PSY - 610)

Lesson40

Brain and Motivational States

Objectives:

To familiarize the students with the

Brain and motivational states

Homeostasis, include temperature regulation, Cellular and brain controls of Thirst, Reward

systems and addictions, Fear, aggression, attachment

Hunger, eating, satiation: brain+ NT control, Body weight set point (Theories), Eating Disorders

Obesity, Anorexia Nervosa.

If we look around us disorders of eating, whether it is obesity or anorexia nervosa, anorexia bulimia

seems to have overwhelmed especially our younger generation (mostly females). To understand why

feeding behaviors goes wrong, there must be some mechanism which ensures that weight remain stable

and when that mechanism breaks down the eating disorders are seen.

Obesity is a major problem of the fast food advanced world. In the US 34 million people are overweight

and 12.5 million people are severely overweight. It is now catching up and China where American fast

food was introduced to Chinese culture (where the body and system was not used to the cooking or the

food) led to an emerging obese younger population. Chinese children are actually being sent to camps to

reduce weight!

Obesity is also genetically linked but this does not explain why or how it has become a disorder of

epidemic nature, with more than double the number of obese people in the world in the 20th century. The

reason may be many a) during evolutionary development as hunters man needed to store fats, plus man

walked many miles, had a lot of physical work which did not fat accumulate. As life became more and

more sedentary this stored fats became unhealthy. Similarly changes in style of cooking, storing food

(now you get frozen foods) earlier women used to spend all day grinding corn or wheat for one meal.

Changes in life styles also made a huge difference--the older generation ate healthy foods and had a

healthy life style, the younger generation prefers to eat fried and fast food and very little exercise! These

are actual findings of a survey that a Behavioral Sciences class I taught carried out: to compare four

generations (their grandparents, parents, themselves and their younger brother and sisters).

Eating Disorders: could be acquired, learnt biological, metabolic, acculturated Acquired:

Children are taught to eat what was given to them and to finish their food. Further they learn to associate

eating with reward (parents promise candy for good behaviors!). Nutrition is not the focus at the

growing age. As people grow older they continue to eat the same kinds of food s that as children/

teenagers/ young adults, even though there is reduced nutritional requirement (and still eat as much!)

Then they tend to store fat. Why don't people stop (check out animals, they do stop!). Because in

humans the inhibitory signals are over ridden, and we continue to eat as the food looks good or tastes

good.

The Psychological variables which lead to overeating have been identified as: field dependence, reduced

impulse control, eats food too fast (too much), maladaptive controls, depression, tension etc.

Innate: obesity is a metabolic disorder. It has been reported by researchers that the reason why it is

difficult for fat people to loose weight is because of metabolic factors. There is basal metabolic rate

difference (some have a higher metabolism rate than others). This is supported by the findings that the

food intake of normals and obese people has not been shown to be significantly different (Rodin et al

1989,). However, there may difference in energy expenditure rates and metabolic states

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Resting metabolic state: diet resistant difficulty in losing weight, even after decreased caloric intake.

Those who diet and binge are setting their bodies at a different metabolic rate. The metabolic rate slows

down with each diet--- making it difficult to lose weight after every diet.

However, there are other factors such as underreporting, underrating eating: "I don't eat a thing, but I

keep gaining weight is something familiar we hear from people who have gained weight.

The simple formula is that if food and fat input= energy expenditure output: balance and weight is

maintained at a constant

Interestingly, 70-80% of a person's energy expenditure is through resting metabolism (Thermogenesis,

fidgeting and maintenance of posture/muscle tone: Non exercise thermo genesis)

Metabolism and energy needed to digest and assimilate food: exercise does not reduce weight but only

facilitates aerobics, and toning of body.

Fasting sends the body into the diet induced thermogenesis

Diet binge- Sporadic Dieting affects body's metabolism by setting it into a starvation mode. The

starvation mode means "we need to save what we have on the body" therefore signals and mechanisms

to store food, store fat come into operation. Once the alteration in metabolic efficiency of the body takes

place, it starts storing fats. Therefore diet binges do not work, if anything they slow down the

metabolism.

Individual differences: Why do some people put on weight more easily than others/ Research ahs

shown that there are special brown adipose tissues which may carry the clue. These convert calories

directly into heat. These are important in animals which hibernate. These animals need this to wake up

in spring. This is known as the Non shivering thermogenesis. These cells rich in mitochondria (explains

why they are high metabolic rate cells!) The mitochondria give these cells the brown color which is why

they are known as brown adipose cells. The B adrenergic receptors control the metabolism of these

cells. Increased Norepinephrine levels lead to increased non shivering thermogenesis leading to heat

production. This mechanism is controlled by the medial hypothalamus. Defect in brown adipose tissue

metabolism leads to defects in the breakdown of fat. It has been reported that in normal rats the

increases in metabolism of brown adipose tissue rises by 200% occurs after a meal, whereas in obese

rats this does not happen. This indicates that deficient meal induced thermogenesis may be involved in

eating disorders.

If each meal increases metabolism, then increase in number of meals would burn more through this

process. This has been suggested and been used as a mechanism for weight reduction.

In extreme cases the relevant therapy for treatment of obesity has been a) jaw wiring: to stop the patient

from eating, or intestinal surgery, which reduces the length of the intestines, or reducing the stomach

size by stapling the stomach (gastroplasty)

Reducing the length of INTESTINES lead to reduced gastric activity, but this can cause a great deal of

discomfort!

We have been talking so far of people who overeat, but there are some people who under eat to the point

of starvation. This is especially true of young women who see models and film artists who have become

thin to be fashionable. This disorder is called Anorexia nervosa. In another form of this disorder young

women eat very little and then binge and throw up forcibly. This disorder is known as Anorexia/

bulimia. Their focus is on food- but in a different way. They like to cook, they like to feed people, they

like to talk food, collect recipes--but they do not eat.

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Neurological Basis of Behavior (PSY - 610)

Anorexia: Is it hereditary or enlarged sulci in the brain (return to normal after recovery), enlarged

ventricles (permanent damage), defect in Dopaminergic, noradrenergic, and brain opioids levels- these

may the biochemical/structural defects which lead to Anorexia? Psychotherapy is not effective but the

anorexic drug Fenfluramine is successful in treating anorexics

Self starvation- This has become part of the modern cultural norms? There have been many famous

cases. One such case is that of a famous American popular singer of the 70's, Karen Carpenter who died

of Anorexia. A bright talented young woman who kept starving herself because she thought she was fat.

More recently cat walk models have been required to go through a weighing process in various shows

around the world to ensure that they are not below required levels of Body weight and Mass.

Thus we have seen that feeding though important for survival can be strongly controlled by social and

other factors in humans.

Thirst: fluid intake

Have you ever thought why do you drink fluids/water, you might answer you do so because you get

thirsty, but then ask yourself where do you feel thirst? In our mouth you would reply, because you feel

dryness in your mouth. Then the question is what would cause this dryness? Dry Salivary glands, you

would answer obviously. The salivary glands dry out because of lowered water level in blood leading to

dryness leading to thirst which would lead to drinking.

Thirst is motivated behavior--it is purposive- animals would continue to seek water when thirsty and

only stop when they have taken water. It is periodic as it appears several times (when the animal eats).

This is almost constant seeking of water as water cannot be stored like fats on our body- there is greater

depletion of fluids

Lets think like a researcher,

1) What if water is injected directly into mouth? It leads to reduced drinking.

2) What if we remove the salivary glands? This leads to dryness of mouth, but no increase in drinking.

So what is drinking or fluid intake controlled by.

For survival, every living organism needs water because each cell in the body and all processes need

fluids for maintaining and cleaning the system one of the most important motivated behaviors is thirst.

For average human adult daily water intake and output equals about 2500 milliliters. Water is lost

through the lungs (vapor), through skin (perspiration) through kidneys (urination) and we input it

through drinking, eating foods with high water content (think of melons, or oranges, even meat is 70%

water). The human body is 50-60% water Sources/mechanism to measure fluid level

It is interesting to note that there are two different mechanisms by which fluid is regulated: the

intracellular and the extracellular.

Intracellular monitors the vascular (blood) and nonvascular (Tissue) fluid components. There are saline

levels of the body fluids in addition to the level of water which is needed to be maintained therefore

constant monitoring of

1) Fluid level

2) 9 % level saline in blood and CSF.

If you recall the sodium levels of ions is high on the extracellular membrane and low in the intracellular

membrane. If sodium ions increase in the intracellular membrane, fluid passes through the cell walls to

dilute salt inside the same would happen if the sodium concentration increases in reverse. Immediately

fluid forms one compartment move to equalize the fluid and osmotic balance on both sides of the

membrane. If fluid is lost form the intracellular membrane it is known as cellular dehydration, and if it

lost from extracellular compartment it is known as hypovolemia. Both lead to thirst and drinking

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Neurological Basis of Behavior (PSY - 610)

Hypothalamic mechanism of fluid works regulation and drinking. Wayner and Carey (1973) have

shown that two separate regions of the hypothalamic receptors are involved in detection or monitoring

of fluid levels.

Cellular dehydration and Osmoreceptors:

For detection of changes in intracellular fluid level, the lateral hypothalamus is involved, and for

detection of changes in the extracellular fluid level the anterior hypothalamus is more sensitive. Fluid

levels in extracellular more important. The fluid level is constantly monitored

When the cellular dehydration takes place the pituitary releases Antidieuretic Hormone and the animal

starts drinking. The Kidney and hormones produced by kidney become important Renin acts on

Angiotensinogen- which produces Angiotensin II- which acts directly on thirst receptors in

Hypothalamus. The Anti diuretic hormone (ADH) released by Anterior Hypothalamus via posterior

pituitary. Increased release of ADH acts on kidneys to retain fluid/decrease urine volume (excretion of

water) and the decreased ADH is a signal to retain fluid output from the body (save body's water). The

water intake help reduce the osmotic pressure and the water is then absorbed by the intracellular

compartment

The Osmoreceptors are located around the Lateral Pre Optic area of the hypothalamus, which can then

send out signals through cellular mechanism and the neural systems.

There are mechanoreceptors which monitor the hypovolemia (extracellular dehydration) and these

monitor the vascular walls for tonic rate of discharge. Some of these are located near the heart and can

monitor the changes in blood pressure (sound familiar?) which results from hypovolemia

There are two mechanisms of thirst and both these are important for maintaining the fluid levels of the

body and ensuring survival and working of the cells.

Loss of fluid from either compartment lead to primary drinking or this is to restore loss of fluid. But

there is drinking in the absence of water loss which is called secondary drinking. This is not in response

to cellular dehydration but dryness of mouth or psychogenic or other pathological reasons

Drinking is therefore one of most important needs of the body's system and research is ongoing for the

NeuroChemicals and hormones that are involved in this behavior.

References:

1. Carlson N.R. (2005) Foundations of Physiological Psychology Allyn and Bacon, Boston

2. Pinel, John P.J. (2003) Biopsychology (5th edition) Allyn and Bacon Singapore

3. Bloom F, Nelson and Lazerson (2001), Behavioral Neuroscience: Brain, Mind and Behaviors (3rd

edition) Worth Publishers New York

4. Bridgeman, B (1988) The Biology of Behaviour and Mind. John Wiley and Sons New York

5. Brown,T.S. and Wallace.(1980) P.M Physiological Psychology

Academic Press New York

6. Mogensen, G.J. (1977) The Neurobiology of Behavior. LawrenceErlbaum Associates

Note: References 5, 6 more closely followed in addition to the references cited in text.

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