🎯 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 🍽️, Body weight set point (Theories) 📊, Obesity 🍔, Anorexia Nervosa 🚫, thirst 💧, bio-rhythms ⏰, Sleep and awakening 😴⏰
- Pathology related to sleep cycles ⚠️
- Sleep disorders and treatment 🩺
- Neurophysiology and biorhythms 🧬⏰, Sleep and awakening cycles 😴🌅, Dreams 💭, Sleep disorders 😴⚠️
⏰ Biological Rhythms
Biological Rhythms: All biological systems are running on some cycle or the other, at any given point in time ⏰🔄. When changes occur in the body or behavioral functioning on a regular basis i.e., rhythmic 🎵, these are called biological cycles and these follow a particular rhythm 📊.
These cycles could be:
- Short within a day (hunger 🍽️)
- Diurnal i.e., of day/night 🌞🌙
- Monthly (menstrual cycle 📅)
- Yearly (reproductive cycle in animals 🦌)
These biological rhythms/cycles have important influence on behaviors of animals 🐾.
📊 Characteristics of Biological Rhythms
1️⃣ Period
Period: This is defined as the time required for a rhythm to be complete ⏱️. This means when a cycle is called a period (from the beginning to the end) 🔄.
2️⃣ Frequency
Frequency: The reciprocal of a period 📈. For example, body temperature reaches a peak once a day 🌡️. The body temperature period would be 24 hours ⏰ and frequency would be once in 24 hours ➡️ 1/24.
There are cycles such as reproductive behavior in animals of 12-month period 📅 with a frequency of one (once a year mating season 🦌) per reproductive cycle.
3️⃣ Amplitude
Amplitude: The amount of change from the original starting point 📊 i.e., 98.4°F + 1°F or 98.4°F + 1.5°F 🌡️. How large is the change from the set point or the original point in the cycle? ⬆️⬇️
There are individual differences in amplitude 👥. One person may have a rise of 0.5°F the other a rise of 1°F degrees 🌡️📈.
4️⃣ Phase
Phase: The peak of the rise in temperature may also be different 🎯. One person may have a peak at 2 p.m. 🕑 another at 3 p.m. 🕒 and still another at 4 p.m. 🕓. Similarly, the drop in temperature may also differ from person to person (gender and metabolism) 👨👩.
The phase is complete with the peak (highest) ⬆️ and trough (lowest) ⬇️. The phase is always with reference to the time of the day 🕐, time of the month 📅, time of the year 📆, or some other external marker 🗓️.
The three people with different peaks would be out of phase with each other ⚡. Similarly, there are those who stay up all night and sleep during the day 🌙😴 and those who sleep at 10 every night and wake up at 5:00 every morning 🌅⏰. These two are totally opposite to each other and out of phase with each other 🔄.
🎛️ Biological Rhythms Control
The biological rhythms/clocks control the functioning of most behaviors that are biological ⏰🧬 including the thermostat 🌡️, female estrus cycles 🐾, the hunger and thirst 🍽️💧, and sleep cycles 😴 and these are entrained with the light/dark cycles 🌞🌙.
🔄 Circadian Rhythms
Circadian rhythms: These are biological rhythm cycles which follow a day cycle 🌍: circadian: Circa: circle 🔄, and dian from diem = of a day 🌅. The daily cycles are many such as temperature 🌡️ and most important (and obvious) of sleep/awakening 😴⏰, feeding 🍽️.
There are other rhythms and cycles, such as the estrous cycle 🐾 (in some animals it appears once a year or so 📅).
🧬 Biological Rhythms Throughout the Body
Studies have shown that there are rhythms for every biological response in the body measured 📊:
- Epidermal (skin temperature) response 🌡️
- Urine 💧
- Blood 🩸
- Whole body temperature 🌡️
- Physical rigor (energy to do work) ⚡
- Weight ⚖️
- Heart rate ❤️
- Blood pressure 🫀
- Respiratory peak flow 🫁
- Growth Hormone levels 📈
- Plasma ACTH (stress hormone levels) 😰
Studies have also shown that body's response to drugs (such as pain killers 💊) also differs with the time of the day ⏰, implying the smaller or larger dose may be necessary for the therapeutic effect 💉.
🏥 Suprachiasmatic Nucleus (SCN)
Suprachiasmatic Nucleus (SCN): The Circadian Rhythms are controlled through the Suprachiasmatic Nucleus (SCN) 🧠 located in the medial hypothalamus 🏥. Lesions in the SCN breaks down the behavioral circadian rhythms in rats 🐀 drinking and adrenal cortisone responses were affected in SCN lesioned rats (Zucker 1972 👨🔬). In hamster 🐹, the estrus cycles (female's ovulatory cycles) are also disrupted ⚠️.
🔄 Phase Shifts
How can our circadian rhythms be changed or influenced: by phase shifts 🔄 (day and night shift workers have not just sleep to take care of but their body adjusts by making changes in the other cycles as well ⏰🌙).
Studies on changes in 12-hour shifts have shown that adaptation of shifts to:
- Heart rate ❤️
- Norepinephrine levels 🧪
- Epinephrine levels 💉
- Body temperature 🌡️
- Stomach enzyme production 🫃
- Performance peaks 📊
were also affected (Higgins 1975 👨🔬) ⚠️.
Menstrual cycles of women were also found to be disrupted if they were traveling across continents and their sleep/awake cycles were disrupted (jet lags?) ✈️😴.
🌙 Day/Night Cycles and Mental Health
Day/Night and dark light cycles also affect mental health 🧠💭. In countries where there are long dark winters ❄️🌑, there is behavioral syndrome known as the winter blues 😔.
Circadian and other biological rhythms are important modulators of behaviors in man and animals 🧬🎭.
🌡️ Body Temperature and Biological Cycle: Circadian
The body temperature is not constant throughout the day 🌡️⏰. Depending on the type of species, whether these are nocturnal (night foragers: night hunter 🌙🦉) or day forager 🌞🦅, their body temperature would rise and fall accordingly 📊.
The temperature peaks whenever the animal is most active ⚡, therefore for the humans 👨, horse 🐴 and other day animals it would peak during the midafternoon 🕑. The rodent rat 🐀 is nocturnal therefore its temperature peaks at night 🌙. Similarly, the lowest temperature would be at night for the day foragers and during day for the nocturnal animals 🌡️⬇️.
⏰ L/D Cycles and Biological Clock
The set point for the body temperature is set by the light/dark cycles 🌞🌙 which set the biological clock ⏰ which in turn sets the biological metabolism (faster during awake ⚡ and slower during sleep 😴 - to save on energy 💾).
Temperature lowest during sleep 🌡️⬇️, because metabolism is lowered 📉. Sleep reduces demand on metabolic heat production 🔥⬇️.
Therefore, the L/D cycles 🌞🌙 set the biological clock ⏰ which in turn sets the temperature-set point 🌡️🎯.
🐻 Hibernation
Hibernation: In some species the thermoregulatory behavior is modulated for longer cycles such as Hibernation ❄️😴. Hibernation is when the animals move into a state where the body temperature is reduced and metabolism slowed to particular level 🌡️⬇️📉.
There is limited requirement of fats etc., and the body can go a long way on the stores of fat 🐻. There are bears 🐻 and other animals which hibernate in winter ❄️ and others such as birds 🦅 which fly away for winters (the Siberian birds migrate towards the Arabian Sea coastal areas for the winters) ✈️🌊.
🍽️ Hunger/Feeding
Among the other important biological systems which have an autonomic modulating mechanism 🎛️, one of the most important ones is hunger 🍴 through which energy ⚡ and nutrition 🥗 is provided to ensure the survival of the organism's systems 🛡️.
Feeding is an essential behavior as provision of nutrients 🥗, energy for survival ⚡ for heat production 🔥 for metabolism 🔄 all depend on what is eaten by the animal 🍽️. Animals must eat enough to maintain their requirement and to maintain body weight ⚖️. If they exceed the input and not use it - it would lead to obesity 🍔, and if they do not take what is required in sufficient amounts it would lead to starvation 🚫.
The seeking of food is hunger - and a very strong motivating behavior 💪. Humans 👨 and animals 🐾 spent most of their awake hours in foraging for food 🔍🍎. Food Seeking is part of the homeostatic systems to regulate the organism internal needs ⚖️🧬.
🎯 Hunger/Feeding as A Motivated Behavior
Food intake/feeding/hunger is motivated behavior 🎭, because feeding behavior:
a) Periodic: ⏰ It is tied with the body's energy consumption 🔥, metabolism 🔄, its needs 📊, the external environment (temperature etc. 🌡️). The signals for onset of feeding and of stopping eating increase and decrease with the internal and external signals and clocks ⏰📡.
b) Priority: 🏆 Feeding has high survival value therefore it takes priority over other behaviors such as mating ❤️. Animals would seek food over seeking others 🍽️>🐾. A hungry man would see the moon as roti 🌙🍞, and the man whose stomach is full can think of the beloved face like the moon 💕🌙.
c) Purposive: 🎯 Very much goal directed when food is sought and animal is hungry 🍴. The behavior would continue till hunger is sated ✅.
d) Persistence: 💪 Food seeking is persistent. It would continue till the goal has been achieved and enough food taken in 🍽️✓.
⚖️ Set Points in Feeding
Although there are many set points within the feeding cycle, there are two major set points which have to be maintained by the feeding behaviors 🎯:
a) Body weight set point: ⚖️ This set point ensures that the body weight is maintained at a constant so if you are 120 or 200 pounds your body works to maintain that weight 📊.
b) Body energy and fat content: 🔥 Within each organism there is a glucose set point 🍬 and a lipid set point 🧈 which the body works to maintain and monitor 📡.
⚖️ Energy Balance Equation
However, remember if the Energy intake is equal to the energy expenditure ⚖️, i.e., Intake = Output 📊, there would be no weight gain. The body weight would be maintained at a constant level ✅.
Weight gain ⬆️ and weight loss ⬇️ would occur if the equation is imbalanced either for input or output of food 🍽️⚖️.
🤔 What Are the Factors Regulating Food Intake?
This is an interesting question ❓ as feeding may occur in the absence of hunger signals 🚫. For example, when we see cakes in a bakery window 🍰, or smell samosas frying 🥟, there is an urge to eat, an immediate desire which overrides the full stomach signals!! 😋 Or we may defer eating because there is a high priority for some other activity (run for life 🏃, or prepare for exams 📚--- food becomes a low priority) 📊.
"Feeding is under a multifactor control and the multiplicity if signals means that there are a number of feedbacks loops for the initiation and termination of food intake" 🔄 (Mogensen and Carlson 1977, p10, cf Mogensen 1980 👨🔬📚).
This can be understood if we look at the body's requirements 📋, that even though glucose 🍬 and fats 🧈 are the main sources of energy ⚡ and metabolism 🔄, there is also need for proteins 🍖 for growth 📈, maintenance 🔧 (and for NT systems 🧪).
🔍 Categories of Feeding Signals
If we analyze them intuitively 🤔, we can identify several possible reasons why we eat and what sets our hunger signals: we feel hungry because 🍽️:
a) We salivate (Pavlovian dogs! 🐕) or our stomach sends signals (rumbles 🫃), or we smell food 👃, or because the body sends signals 📡. These can be classified into the following categories:
Oral 👄, /Peripheral 🔄, (also odor 👃) Gastric 🫃 and Metabolic (neural 🧠)
👄 Oral/Peripheral Factors
Oral/peripheral factors: The taste 😋, odor 👃, sight 👁️ and texture 🤚 of food has role (though small) in the control of food intake 🍽️. Animals eat more if the food looks and tastes good 🍰, and less if the food tastes bad 🤢.
Mouth palatability (how good it tastes and looks 😋) and variety 🎨: increases food intake in rats 🐀 and humans 👨 alike. Palatability is a very important source of obesity 🍔 – eating when not required by the body ⚠️.
🐀 Rat Studies on Palatability
Rats like high fat foods 🧈 very much, and increased total feeding response, and become obese 🐀📈, the same for mice 🐭. Rats would eat quinine adulterated food only if they are starving 🚫 (wouldn't anyone else?) 🤔
🧪 Teitlebaum and Epstein (1962) Experiment
Teitlebaum and Epstein (1962) 👨🔬 inserted a nasopharyngeal gastric tube which by passed the mouth region 👃🚫👄. Rats were trained to send food through tube to stomach 🐀💉- their intake is only how much required to maintain body weight ⚖️.
Therefore, more than mouth and the stomach region are involved in feeding 🧠🫃. Snowdon (1969) 👨🔬 report that rats maintain lower than normal weight levels ⬇️ if food is not routed through mouth (oral) 👄🚫.
There are some signals from the mouth 👄, (odor 👃 and taste 😋).
💉 Nickoliadis and Rowland (1976) Study
Another study of eliminating oral factors on food intake is to administer nutrients through intravenous infusions 💉. Experiments by Nickoliadis and Rowland (1976) 👨🔬 "When infusion equaled or was greater than the normal daily intake, there was an increase of oral intake of the diet 📈…" indicating that there were some oral factors involved in feeding 👄🍽️.
Sight of Food 👁️🍰 stimuli also leads to an initiation of an increase in eating response even when sated or full 😋.
🧠 Experience and Cognitive Factors
In man and higher mammalians 🧠, the experience and cognitive factors are important in feeding behaviors 💭🍽️. Therefore, eating different foods 🍜🍱🍕, raw or cooked 🔥, liking Chinese 🥡, Japanese 🍣, Thai 🍜, Greek 🥙, Ethiopian food 🍲 is learnt 📚. Using different cooking spices 🌶️ are also learnt 🧑🍳.
The taste aversions are also learnt 🚫 such as cultural 🏛️, religious ⛪ and other constraints 📋. There are some animals such as snakes 🐍, frogs 🐸 and lizards 🦎 not thought edible in majority of the developed world 🌍 but there are some cultures where these are relished! 😋 We may like the head of the goat and trotters (siri paiy) 🐐 but they may not be the food of choice in most countries 🌍.
What we eat 🍽️, how we eat (chopsticks 🥢/ knives 🔪 or forks 🍴 or banana leaves and hands 🫱), cooked or uncooked 🔥, vegetarian or meat 🥗🥩 depends on our region 🌍.
Therefore, human food and eating is determined by cultural, religious and regional factors 🏛️⛪🌍.
📚 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