๐ฏ Objectives
To familiarize the students with the:
- Brain and motivational states ๐ง ๐ญ
- Homeostasis โ๏ธ, include temperature regulation ๐ก๏ธ, Cellular and brain controls of Thirst ๐ง, Reward systems and addictions ๐, Fear ๐จ, aggression ๐ก, attachment โค๏ธ
- Hunger ๐ฝ๏ธ, eating, satiation: brain+ NT control ๐ง ๐งช, Body weight set point (Theories) ๐, Eating Disorders Obesity ๐, Anorexia Nervosa ๐ซ
โ ๏ธ Eating Disorders
If we look around us disorders of eating ๐ฝ๏ธโ ๏ธ, whether it is obesity ๐ or anorexia nervosa ๐ซ, anorexia bulimia ๐คฎ seems to have overwhelmed especially our younger generation (mostly females ๐ฉ). To understand why feeding behaviors goes wrong โ, there must be some mechanism which ensures that weight remain stable โ๏ธ and when that mechanism breaks down โ ๏ธ the eating disorders are seen ๐ฝ๏ธโ.
๐ Obesity
Obesity is a major problem of the fast-food advanced world ๐๐. In the US ๐บ๐ธ 34 million people are overweight โ๏ธโฌ๏ธ and 12.5 million people are severely overweight ๐. It is now catching up and China ๐จ๐ณ where American fast food was introduced to Chinese culture (where the body and system was not used to the cooking or the food ๐๐ฅค) led to an emerging obese younger population ๐ฆ๐. Chinese children are actually being sent to camps to reduce weight! ๐๏ธโฌ๏ธ
๐งฌ Genetic and Environmental Factors
Obesity is also genetically linked ๐งฌ but this does not explain why or how it has become a disorder of epidemic nature ๐โ ๏ธ, with more than double the number of obese people in the world in the 20th century ๐โฌ๏ธ.
The reason may be many:
a) During evolutionary development as hunters man needed to store fats ๐น๐ง, plus man walked many miles ๐ถโฌ๏ธ, had a lot of physical work which did not fat accumulate โก. As life became more and more sedentary ๐ช these stored fats became unhealthy โ ๏ธ.
Similarly changes in style of cooking ๐งโ๐ณ, storing food ๐ฅซ (now you get frozen foods โ๏ธ๐) earlier women used to spend all day grinding corn or wheat for one meal โฐ. Changes in life styles also made a huge difference ๐โthe older generation ate healthy foods ๐ฅ and had a healthy life style ๐ช; the younger generation prefers to eat fried and fast food ๐ and very little exercise! ๐ซโก
These are actual findings of a survey that a Behavioral Sciences class I taught carried out ๐: to compare four generations (their grandparents ๐ด๐ต, parents ๐จ๐ฉ, themselves ๐ฆ๐ง and their younger brother and sisters ๐ถ).
๐ Eating Disorders: Could Be Acquired, Learnt, Biological, Metabolic, Acculturated
๐ Acquired
Children are taught to eat what was given to them and to finish their food ๐ถ๐ฝ๏ธโ . Further they learn to associate eating with reward ๐ (parents promise candy ๐ฌ for good behaviors!). Nutrition is not the focus at the growing age ๐ซ๐ฅ.
As people grow older ๐จ, they continue to eat the same kinds of foods that as children/teenagers/young adults ๐๐, even though there is reduced nutritional requirement โฌ๏ธ๐ฅ (and still eat as much! ๐ฝ๏ธโฌ๏ธ) Then they tend to store fat ๐ง๐. Why don't people stop (check out animals ๐พ, they do stop! ๐). Because in humans the inhibitory signals are over ridden โ๐ก, and we continue to eat as the food looks good or tastes good ๐๏ธ๐.
๐ง Psychological Variables
The Psychological variables which lead to overeating have been identified as ๐:
- Field dependence ๐
- Reduced impulse control โ ๏ธ๐ฏ
- Eats food too fast (too much) ๐ฝ๏ธโก
- Maladaptive controls ๐๏ธโ
- Depression ๐
- Tension ๐ฐ
๐งฌ Innate: Obesity as a Metabolic Disorder
Innate: obesity is a metabolic disorder ๐ฅโ ๏ธ. It has been reported by researchers that the reason why it is difficult for fat people to lose weight is because of metabolic factors โ๏ธ๐ฅ. There is basal metabolic rate difference (some have a higher metabolism rate than others โก๐).
This is supported by the findings that the food intake of normal and obese people has not been shown to be significantly different (Rodin et al 1989 ๐จโ๐ฌ๐). However, there may difference in energy expenditure rates โก๐ and metabolic states ๐ฅโ๏ธ.
โก Resting Metabolic State
Resting Metabolic State: diet resistant ๐ซโ๏ธ difficulty in losing weight โฌ๏ธ, even after decreased caloric intake ๐ฝ๏ธโฌ๏ธ. Those who diet and binge ๐ are setting their bodies at a different metabolic rate โก๐. The metabolic rate slows down with each diet โฌ๏ธโฌ๏ธ--- making it difficult to lose weight after every diet โ ๏ธ.
However, there are other factors such as underreporting, underrating eating ๐โฌ๏ธ: "I don't eat a thing, but I keep gaining weight ๐ฝ๏ธ๐ซโ๏ธโฌ๏ธ is something familiar we hear from people who have gained weight ๐ญ.
โ๏ธ Energy Balance Formula
The simple formula is that if food and fat input = energy expenditure output: balance and weight is maintained at a constant โ๏ธโ
Interestingly, 70-80% of a person's energy expenditure is through resting metabolism ๐ฅ๐ (Thermogenesis, fidgeting ๐คธ and maintenance of posture/muscle tone ๐ช: Non exercise thermogenesis โก)
Metabolism and energy needed to digest and assimilate food ๐ฝ๏ธ๐ฅ: exercise does not reduce weight โก๐ซโฌ๏ธ but only facilitates aerobics ๐, and toning of body ๐ช.
๐ซ Fasting and Diet-Binge Cycle
Fasting sends the body into the diet induced thermogenesis ๐ฅโฌ๏ธ
Diet Binge- Sporadic Dieting ๐ affects body's metabolism by setting it into a starvation mode ๐ซ๐ฝ๏ธ. The starvation mode means "we need to save what we have on the body" ๐พ therefore signals and mechanisms to store food, store fat come into operation ๐งโฌ๏ธ. Once the alteration in metabolic efficiency of the body takes place โก๐, it starts storing fats ๐ง๐. Therefore, diet binges do not work โ, if anything they slow down the metabolism โฌ๏ธ๐ฅ.
๐ฅ Individual Differences: Brown Adipose Tissue
Individual Differences: Why do some people put on weight more easily than others? ๐คโ๏ธ
Research has shown that there are special brown adipose tissues ๐ค which may carry the clue ๐. These convert calories directly into heat ๐ฅ. These are important in animals which hibernate ๐ปโ๏ธ. These animals need this to wake up in spring ๐ธ. This is known as the Non shivering thermogenesis ๐ฅ๐ซ๐ฅถ.
These cells rich in mitochondria โก (explains why they are high metabolic rate cells! ๐ฅโฌ๏ธ) The mitochondria give these cells the brown color ๐ค which is why they are known as brown adipose cells ๐ค๐งฌ. The ฮฒ adrenergic receptors control the metabolism of these cells ๐๏ธ.
๐งช Norepinephrine and Thermogenesis
Increased Norepinephrine levels ๐งชโฌ๏ธ lead to increased non shivering thermogenesis leading to heat production ๐ฅโฌ๏ธ. This mechanism is controlled by the medial hypothalamus ๐ง ๐ฅ.
Defect in brown adipose tissue metabolism leads to defects in the breakdown of fat โ ๏ธ. It has been reported that in normal rats ๐ the increases in metabolism of brown adipose tissue rises by 200% ๐ occurs after a meal ๐ฝ๏ธ, whereas in obese rats this does not happen โ. This indicates that deficient meal induced thermogenesis may be involved in eating disorders โ ๏ธ๐.
If each meal increases metabolism ๐ฝ๏ธโก๏ธ๐ฅโฌ๏ธ, then increase in number of meals would burn more through this process ๐ฝ๏ธ๐ฝ๏ธ๐ฝ๏ธโก๏ธ๐ฅโฌ๏ธ. This has been suggested and been used as a mechanism for weight reduction โฌ๏ธโ๏ธ.
๐ฅ Extreme Treatments for Obesity
In extreme cases the relevant therapy for treatment of obesity has been โ ๏ธ๐ฅ:
- a) Jaw wiring ๐ง: to stop the patient from eating ๐ซ๐ฝ๏ธ, or
- Intestinal surgery ๐ฉบ, which reduces the length of the intestines ๐ซโ๏ธ, or
- Reducing the stomach size by stapling the stomach (gastroplasty) ๐ซ๐
Reducing the length of INTESTINES lead to reduced gastric activity ๐ซโฌ๏ธ, but this can cause a great deal of discomfort! ๐ฃโ ๏ธ
๐ซ Anorexia Nervosa
Anorexia Nervosa: We have been talking so far of people who overeat ๐ฝ๏ธโฌ๏ธ, but there are some people who under eat to the point of starvation ๐ซ๐ฝ๏ธ๐. This is especially true of young women ๐ฉ who see models ๐ธ and film artists ๐ฌ who have become thin to be fashionable ๐. This disorder is called Anorexia nervosa ๐ซ๐ฝ๏ธ.
In another form of this disorder young women eat very little and then binge and throw up forcibly ๐คฎ. This disorder is known as Anorexia/bulimia ๐๐คฎ.
๐ณ Characteristics of Anorexia
Their focus is on food-but in a different way ๐ฝ๏ธ๐ฏ. They like to cook ๐งโ๐ณ, they like to feed people ๐จโ๐ณโก๏ธ๐ฅ, they like to talk food ๐ฌ๐, collect recipes ๐๐ฒโbut they do not eat ๐ซ๐ฝ๏ธ.
๐งฌ Biological Factors in Anorexia
Anorexia: Is it hereditary ๐งฌ or enlarged sulci in the brain ๐ง ๐ (return to normal after recovery โ ), enlarged ventricles ๐ง ๐ต (permanent damage โ ๏ธ), defect in Dopaminergic, noradrenergic, and brain opioids levels ๐งช- these may the biochemical/structural defects which lead to Anorexia? ๐ค
Psychotherapy is not effective โ๐๏ธ but the anorexic drug Fenfluramine ๐ is successful in treating anorexics โ .
๐ Self-Starvation and Cultural Norms
Self-starvation ๐ซ๐ฝ๏ธ- This has become part of the modern cultural norms? ๐๐บ There have been many famous cases. One such case is that of a famous American popular singer of the 70's, Karen Carpenter ๐ค who died of Anorexia ๐. A bright talented young woman who kept starving herself because she thought she was fat ๐ซ๐ฝ๏ธ๐.
More recently cat walk models ๐ have been required to go through a weighing process in various shows around the world ๐โ๏ธ to ensure that they are not below required levels of Body weight and Mass ๐โ ๏ธ.
Thus, we have seen that feeding though important for survival ๐ก๏ธ can be strongly controlled by social and other factors in humans ๐ง ๐.
๐ง Thirst: Fluid Intake
Have you ever thought why do you drink fluids/water ๐ง, you might answer you do so because you get thirsty ๐ค, but then ask yourself where do you feel thirst? โ In our mouth ๐ you would reply, because you feel dryness in your mouth ๐ถ. Then the question is what would cause this dryness? ๐ค Dry Salivary glands ๐งโฌ๏ธ, you would answer obviously. The salivary glands dry out because of lowered water level in blood ๐ฉธ๐งโฌ๏ธ leading to dryness leading to thirst which would lead to drinking ๐ง๐ฅค.
๐ฏ Thirst as Motivated Behavior
Thirst is motivated behavior ๐ญ๐งโit is purposive ๐ฏ- animals would continue to seek water when thirsty ๐พ๐ง and only stop when they have taken water โ . It is periodic โฐ as it appears several times (when the animal eats ๐ฝ๏ธ). This is almost constant seeking of water ๐ง๐ as water cannot be stored like fats on our body ๐งโ- there is greater depletion of fluids ๐งโฌ๏ธ.
๐งช Testing Thirst Mechanisms
Let's think like a researcher ๐จโ๐ฌ:
1) What if water is injected directly into mouth? ๐ง๐๐ It leads to reduced drinking โฌ๏ธ๐ง.
2) What if we remove the salivary glands? ๐ซ๐ง This leads to dryness of mouth ๐ถ, but no increase in drinking ๐งโฌ๏ธโ. So, what is drinking or fluid intake controlled by ๐ค๐๏ธ.
๐ง Water Balance in the Body
For survival ๐ก๏ธ, every living organism needs water ๐ง because each cell in the body and all processes need fluids for maintaining and cleaning the system ๐งฌ. One of the most important motivated behaviors is thirst ๐ญ๐ง.
For average human adult daily water intake and output equals about 2500 milliliters ๐ง๐. Water is lost through:
- The lungs (vapor) ๐ซ๐จ
- Through skin (perspiration) ๐ฆ
- Through kidneys (urination) ๐ฝ
And we input it through:
- Drinking ๐ง๐ฅค
- Eating foods with high water content ๐๐ (think of melons, or oranges, even meat is 70% water ๐ฅฉ๐ง)
The human body is 50-60% water ๐ง๐จ.
๐ฌ Two Mechanisms of Fluid Regulation
Sources/mechanism to measure fluid level: It is interesting to note that there are two different mechanisms by which fluid is regulated ๐๏ธ๐ง: the intracellular ๐งฌ and the extracellular ๐.
Intracellular monitors the vascular (blood) ๐ฉธ and nonvascular (Tissue) ๐งฌ fluid components. There are saline levels of the body fluids in addition to the level of water which is needed to be maintained ๐ง๐ง therefore constant monitoring of:
- 1) Fluid level ๐ง๐
- 2) 9% level saline in blood and CSF ๐ง๐
๐ง Osmotic Balance
If you recall the sodium levels of ions is high on the extracellular membrane โฌ๏ธ and low in the intracellular membrane โฌ๏ธ. If sodium ions increase in the intracellular membrane ๐งโฌ๏ธ, fluid passes through the cell walls to dilute salt ๐งโก๏ธโ inside the same would happen if the sodium concentration increases in reverse ๐.
Immediately fluid forms one compartment move to equalize the fluid and osmotic balance on both sides of the membrane โ๏ธ๐ง. If fluid is lost form the intracellular membrane it is known as cellular dehydration ๐งฌ๐งโฌ๏ธ, and if it lost from extracellular compartment it is known as hypovolemia ๐๐งโฌ๏ธ. Both lead to thirst and drinking ๐ง๐ฅค.
๐ง Hypothalamic Mechanism of Fluid Regulation
Wayner and Carey (1973) ๐จโ๐ฌ have shown that two separate regions of the hypothalamic receptors are involved in detection or monitoring of fluid levels ๐ง ๐ก:
๐ง Cellular Dehydration and Osmoreceptors
For detection of changes in intracellular fluid level ๐งฌ๐ง, the lateral hypothalamus ๐ง ๐ฅ is involved, and for detection of changes in the extracellular fluid level ๐๐ง the anterior hypothalamus ๐ง ๐ฅ is more sensitive. Fluid levels in extracellular more important ๐. The fluid level is constantly monitored ๐กโฐ.
๐ ADH and Kidney Function
When the cellular dehydration takes place ๐งฌ๐งโฌ๏ธ the pituitary releases Antidiuretic Hormone (ADH) ๐ and the animal starts drinking ๐ง๐ฅค. The Kidney ๐ฅ and hormones produced by kidney become important:
Renin acts on Angiotensinogen ๐งช- which produces Angiotensin II ๐งช- which acts directly on thirst receptors in Hypothalamus ๐ง ๐ก.
The Anti diuretic hormone (ADH) ๐ released by Anterior Hypothalamus ๐ง ๐ฅ via posterior pituitary ๐ฅ. Increased release of ADH acts on kidneys to retain fluid/decrease urine volume ๐ฝโฌ๏ธ (excretion of water ๐ง) and the decreased ADH is a signal to retain fluid output from the body ๐พ๐ง (save body's water). The water intake help reduce the osmotic pressure and the water is then absorbed by the intracellular compartment ๐งโก๏ธ๐งฌ.
๐ก Osmoreceptors Location
The Osmoreceptors ๐ก are located around the Lateral Pre-Optic area of the hypothalamus ๐ง ๐ฅ, which can then send out signals through cellular mechanism and the neural systems ๐ก๐งฌ.
There are mechanoreceptors ๐๏ธ which monitor the hypovolemia (extracellular dehydration ๐๐งโฌ๏ธ) and these monitor the vascular walls for tonic rate of discharge ๐ฉธ๐. Some of these are located near the heart โค๏ธ and can monitor the changes in blood pressure ๐ซ๐ (sound familiar?) which results from hypovolemia โ ๏ธ.
๐ง Primary vs Secondary Drinking
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 ๐ก๏ธ๐งฌ.
Loss of fluid from either compartment lead to primary drinking ๐งโก๏ธ๐ฅค or this is to restore loss of fluid ๐. But there is drinking in the absence of water loss which is called secondary drinking ๐งโ. This is not in response to cellular dehydration but dryness of mouth ๐ถ or psychogenic ๐ง or other pathological reasons โ ๏ธ.
Drinking is therefore one of most important needs of the body's system ๐ก๏ธ๐ง and research is ongoing for the Neurochemicals ๐งช and hormones ๐ that are involved in this behavior ๐ฌ.
๐ References
- Carlson, N. R. (2005). Foundations of physiological psychology. Pearson Education New Zealand.
- Pinel, J. P. (2003). Biopsychology. (5th ed). Allyn & Bacon Singapore.
- Bloom, F., Nelson., & Lazerson. (2001), Behavioral Neuroscience: Brain, Mind and Behaviors. (3rd ed). Worth Publishers New York
- Bridgeman, B. (1988). The Biology of Behavior and Mind. John Wiley & Sons, New York
- Brown, T.S. & Wallace, P.S. (1980). Physiological Psychology. Academic Press, New York
- Mogensen, G. J. (1977). The Neurobiology of Behavior. Lawrence Erlbaum Associates