Brain and Motivational States:Biological Rhythms, Circadian rhythms, Hunger/Feeding

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Brain and Motivational States:Gastric factors, Lipostatic theory, Neural Control of feeding >>

Neurological Basis of Behavior (PSY - 610)

Lesson38

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, 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:

All biological systems are running on some cycle or the other, at any given point in time. When changes

occur in the body or behaviorual 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), or

diurnal i.e. of day/night or could be monthly (menstrual cycle), or yearly (reproductive cycle in

animals). These biological rhythms/cycles have important influence on behaviors of animals

The characteristics of biological rhythms:

1. Period: This is defined as the time required for a rhythm to be complete. This mean when a cycle is

called a period (from the beginning to the end)

2. Frequency: The reciprocal of a period e.g. body temperature reaches a peak once a day. The body

temperature period would be 24 hours and frequency would be once in 24 hours. There are cycles such a

reproductive behaviors in animals of 12 month period with a frequency of one (once a year mating

season) per reproductive cycle.

3. Amplitude: is the amount of change from the original starting point i.e. 98.40+1 F or 98.40+1.50 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 .5F the other a rise of 1F degrees

4. 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 4p.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

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.

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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)

Studies have shown that there are rhythms for every biological response in the body measured: the

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, and even

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.

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.

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,

epinephrine levels, body temperature, stomach enzyme production, and performance peaks also were

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 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 (of a day)

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 mid afternoon. 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. 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? In some

species the thermoregulatory behavior is modulated for longer cycles such as Hibernation. Hibernation

is when the animals moves 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)

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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

Hunger/Feeding

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 sue 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.

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.

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

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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).

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: 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. Palatibility is a very important source of obesity eating when not required by the body

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) 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).

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 and increase in eating response even when sated or

full.

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:

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

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

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

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