Human behavior

Psychology of Behavior

According to Sigmund Freud, (1856-1939), human beings are just mechanical creatures, whom he views as prisoners of primitive instincts and powers, which we can barely control. He states that our purpose is to control these instincts and powers.

“The soul is like an iceberg; it contains a conscious part and an unconscious part.”

His life
Living from 1856 to 1939, numerous scientific discoveries took place during his life. When Freud was still young, Darwins’ The Origins of Species was published, and Fechner came up with the underlying basics of psychology.

Developments such as these had a tremendous effect on Freud’s thoughts, yet the German, Helmholtz, was probably the person who had the greatest influence on Freud’s way of thinking by drawing up the law of preservation of energy. This discovery is most likely the reason Freud started looking at people as a closed system of psychic energy that is floating between the conscious and the unconscious part of the human spirit.

The iceberg

Freud explained these concepts by comparing the human spirit to an iceberg. The visible part of the iceberg (spirit) is the conscious part, which consists of everything we know and remember and the thinking processes through which we function.

The unconscious part is made up of everything we have ever learned or experienced, including that which has been “forgotten”. A part of these forgotten things are really gone, but the largest part of the unconscious has just been shut out, because it would be annoying to be consciously reminded of it.

The influences of Helmholtz are also visible at other points. According to Freud, the material in the unconscious contains psychic energy. This psychic energy is constantly trying to get into the conscious part, while the conscious part keeps using energy to suppress undesirable discoveries. An expression of unknown powers is, for example, slips of the tongue. These expressions show that our unconscious was not strong enough to keep these powers outside the conscious part.

Id, Ego and Superego

Now we are going back to the theory of the id, the ego and the superego. The spirit of a newborn child just has an id, the instinctive incentives and reflexes that the human beings have developed during the last centuries. The only function of the id is to respond to the incentives. The ego develops itself from the id and from the discovery that the behavior of the id can have tedious results. The superego, a result of a person’s socialization, is basically just the conscience, which mediates between needs of the id and the ego. When you are getting older, you start to develop more and more values.


Erikson (1902-1994), who mainly did research on children, teenagers, immigrants and fugitives, has become famous by his notion of identity. He said that the identity crisis is the largest in each of these groups. It has been scientifically proven that young people who are living on their own for the first time are experiencing a lot of fear and doubt. They are wondering who they are and what they are living for.

“Identity is something individual, it arises from our past and our descent.”

Our identities are very personal and develop from our heritage and history. A person’s identity is, therefore, a result of origin, such as Catholic, Jewish, Chinese, etc. The quality of that origin also has influence, so Prince Charles will have a completely different identity than an underclass citizen.

Creation of identity
Erikson distinguishes different phases by the creation of identity. He thinks the first years of life have a big influence on the consciousness of our identity, because it is during this period that we develop trust. The second year is important because the child develops an autonomous drive, and, during the third year, the child develops initiative, which is controlled by the conscience (You can see a clear resemblance to the theory of Freud.). Throughout school, the child develops a consciousness of constructiveness. In other words, children like to do things with others and to imitate others. When puberty is reached, an identity crisis causes the adolescent to look for ideas to believe in. He/she looks for groups to which he/she can belong and for groups through which the adolescent can discover his/her own wishes. Sometimes one adapts to a certain group to an extent that causes his/her own identity to be almost lost.


His life

Alfred Adler (1870-1937) began as a pupil and supporter of Sigmund Freud; however, after a while, serious differences of opinion developed between the two, leading to a separation in 1911. Adler then started to develop his own theories, which did not receive serious recognition until the fifties. This school was called individual psychology.

“Human beings have a strong will to overcome a sense of inferiority.”

His theory
Adler had only a few followers, and, after his death, this group vanished completely. Today, very few psychologists are really engaged in his ideas, but, at the same time, many psychologists adapt pieces of Adlers notions. Adler’s ideas reflect the experiences from his youth, in which he often suffered from diseases, and his bodily development fell behind that of others. As a result, Adler developed a very strong desire to surmount these disadvantages, and, from this, he concluded that people possess a great strength that allows them to overcome a sense of inferiority. During his study, he investigated various possibilities to compensate for the malfunctioning parts of the body. For example, someone who is unable to see with one of his/her eyes will attain better eyesight in the remaining eye. Adler developed a theory in which aggression was the vehicle used by people to overcome mechanical shortages by compensation. According to Adler, mental diseases had no biological cause but were instead caused by a patient’s desire to overcome his/her sense of inferiority.

Adler did some important research on rivalry, and, therefore, he investigated the rank order between children in the same family. He stated that the oldest child faces the danger of being dethroned, because he is the eldest and expectations are higher. The second child has the danger of developing a sense of inferiority, so, to compensate for this, he/she strives to become better. This child develops values and norms and draws up a plan for his life. He/she works toward the realization of this plan for the remainder of his/her life. This plan is unique to the individual, and it is from this characteristic of individualism that the term “individual psychology” is derived.


His life
Carl Rogers (1902-1987) grew up in Illinois. He was already interested in agriculture when he was still an adolescent. He started his study in agriculture, but after a while he started to get more interested in psychology and he changed his study. He graduated in 1931 in clinical psychology.
Rogers was very pragmatic. This appears from his way of working: Instead of first designing a theory and then a therapy, he started with a therapy, before he started to think about a theory that would prove that the theory worked (or didn’t work).

“Human beings are intrinsically good and friendly.”

Rogers told his method to everyone that was willing to investigate it. This is remarkable too because psychologists usually keep their theories a secret to prevent others to have success with their theory. Rogers even made tapes of his therapeutic sessions. He asked everyone to criticize his methods.
Another remarkable aspect of his way of treatment was that he could demonstrate real improvements with his patients. Something that other therapists often couldn’t.

Roger’s theory
Rogers believes in the genetic origin of kindness of human beings. He even says that if we are left by ourselves we will be nice and friendly people. If we are unkind, selfish or annoying to other people in any other way, we are doing this just because we have learned this by others.

The basis of Rogers’ theory is that every human act is based on the use of the action (After all it is useful to be nice to others so that they are willing to help you when you need them). It is also a human desire to try to unfold his talents and be the best in something.



The development of her theory
Karen Horney (1885-1952) is one of the most important persons from the neo-Freudian trend. Her ideas are comparable with the ideas of Erich Fomm and Harry Sullivan. They all stressed the importance of culture in the mind.

“Human beings have neurotic needs, that can result into neuroses when not satisfied.”

Horney had much criticism on Freud, she thought his theories were unnecessarily pessimistic about the nature of human beings. This criticism formed the basis of her own theory, in which the influence of the social environment and the culture forms the basis of human behavior.

Her theory
Horney began her theory with the notice that there could be no universal behavior. Because things that are normal in one culture, could be completely insane in another.
Horney’s theory especially applies to neuroses. A neurosis is an emotional disturbance, which comes from unsolved problems of life. It is caused by a conflict situation. An example of this is a fighting neurosis. This situation can arise when a soldier has to risk his life to save somebody, whom he does not respect, at the expense of other people he does respect. According to Horney a neurosis is always a character-neurosis. A character-neurosis arises, according to Horney from frustrations, for example when you feel ignored, helpless, unimportant or betrayed. This feeling arises during the childhood when parents neglect their children.

To prevent such a neurosis, Horney formulated a number of needs: Four of them are dominant:

  • a need for affection
  • a need for power
  • a need for retirement
  • a need for subjection

Horney received much more recognition by the public at large than with her colleagues. Probably because she explained behavior with logical and easy to understand causes. The latter was caused by her habit to oversimplify things. Apart from this critics, Karen Horney contributed a lot in the explanation of human behavior.


His theory
According to Burrhus F. Skinner (1904-1990) our whole behavior is learned. Behavior that is a threat to the Ich can be changed by a simple learning habit. This approach to mental illnesses, which is called the learning model is almost completely developed by the psychologist Skinner.

“Our behavior is affirmed by positive reinforcement.”

The learning theory is a part of psychology, a division of science that started with the old Russian psychologist Pavlov.

Pavlov did a famous experiment with a dog. He taught the dog to produce mucus when hearing the sound of a chime. With this experiment he proved that you could teach a dog illogical and unreasonable behavior. Later Pavlov found out this reflex also works with human beings.

Another important learning process is the instrumental learning, which means learning to solve problems. Trying to avoid problems is an important part of it. Psychologists found out that the behavior to avoid something undesirable is a learned behavior. For example, if you know you can expect an angry neighbor if you turn on your music very loud, you will not do this again.

Skinner also developed the theory of confirmation. He came up with it as a result of an experiment with a pigeon that had to push a button to get a grain of corn. Skinner saw that the pigeon learned very fast to pick if he got a grain of corn for every pick (this grain of corn is called confirmation). Skinner also discovered the pigeon quitted as soon as he did not get any corn for his picking anymore. If he just got a granule of corn every once in a while he learned more slowly. This experiment had some major consequences. Imagine a thief getting caught 1 out of 10 times. The other 9 times he will experience confirmation, so he will probably continue to steal.


The development of his theory
Abraham Maslow (1908-1970) is the founder of the so-called humanist(ic) psychology or social learning psychology. This school in psychology is called learning psychology, because the principals are applied on social relations. It is sometimes seen as the “third road” within psychology, because he has obviously chosen a very different direction than the supporters of Freud and Skinner.

“Humans cannot live without needs, they tend to appease them all.”

Maslows greatest contribution to the psychology has been his search for common sense.

He thought that the best way to find out what went wrong with “wrong” people is to study healthy people first. He criticized many different movements. He blamed Freud for focusing mainly on mental illnesses and he blamed Skinner for basing his theory too much on animals.

Maslow found out that people have certain needs. He categorized these needs in groups with different rankings:

  1. Physical needs. These are needs that are necessary to stay alive. Examples are food, drinks and oxygen.
  2. Safety needs. These needs are most visible when studying children, but order and stability are also important for adults.
  3. Love needs and the need to belong. Examples are the need for friends and love.
  4. . Aesthetic needs. An example of this need for beauty is the desire to embellish your home instead of just living in it (physical need).

People are inclined to satisfy these needs. But, A person “rarely achieves a state of total satisfaction, unless for a short term”.


His life
Victor Frankl(1905-1997) has been in a nazi camp during the second world war he says he came to the core of life because he experienced beastly situations.

“Every person searches for a meaning to live, which gives a positive drive to live.”

He developed a theory, called logotherapy, as a result of the brutal things he experienced during his time in the concentration camp. In his book Frankl often quoted the German philosopher Nietschze, who for example said: “Everyone who has a why to live for, can bear almost every how.”

Logotherapy focuses on the future. Frankl claims that human beings are free to choose. A neurosis (see Horney) does not evolve out of a conflict between drives and instincts, but out of a conflict between different values.

A part of logotherapy is called dereliction. Frankl taught patients to think more about themselves instead of others. Another part is sometimes called “reversed psychology”. According to this, you should try to keep someone suffering from insomnia awake as long as possible. Frankl’s theory suggests that the person will eventually start to feel sleepy, because “the key to healing is the obligation to yourself”.

According to Frankl everyone has his own purpose in life, a purpose that drives him through life. There are three ways to discover this purpose: to do a deed, to experience a certain value or to suffer. Frankl also recognizes a super purpose, a live in the hereafter. He says that every person, who believes in the hereafter, tries the best he can to acquire a nice place there.


Philosophers in the seventeenth and eighteenth century (like Descartes and Hobbes)

shared a mechanistic view. They thought that some of our actions are the result of internal or external forces, which are not under voluntary control. Hobbes, for example, claimed that underlying reasons for behavior are the avoidance of pain and the quest for pleasure.

“Behavior is the result of instincts, which are present since birth.”

The extreme of the mechanistic view is the theory of instincts. An instinct is an innate biological force, which commands the organism to behave in a particular way. The main advocate of the instinct theory was the psychologist McDougall. He hypothesized that all thinking and behavior is the result of instincts, which are fixed from birth, but which can be adjusted by learning and experience.
In his book Social Psychology McDougall enumerated several instinctive drives, like fear, curiosity, aggression and reproduction.
This list was expanded later with 8 other instincts. By changes and combinations of instincts he tried to explain the whole repertoire of human behavior.

The instinct theory was supported by many psycho-analysts. For example, Freud asserted that human behavior could be explained by two major instincts: the instinct to survive (such as a drive for sexual reproduction) and the instinct to avoid death, which causes aggression.

Quite soon, it became evident that many instincts were required to explain human behavior and, even worse, these instincts did not explain very much: so many instincts were postulated such that any type of behavior could be explained. A better phrasing would be to say that instincts provide a description of behavior, rather than an explanation.

In the 1920′s instinct theory was replaced by the theory of drives. A driving force originates from a natural need, like thirst. Such a situation stimulates the organism to comply with the need. Lack of food causes chemical changes in the blood, which causes the need for food, which stimulates the organism to look for food.


In the 1950′s psychologists started to question the validity of the drive reduction theory. Gradually they realized that external inputs and drives affected behavior of organisms, in addition to the internal drives. A good example is motivation, which corresponds to the state of an organism to start or to continue an act.

“A motivation is an interaction between stimuli from outside and the needs of an organism.”

Incentives can be better understood as an interaction between external inputs and needs of an organism. An example is a beautiful display with cakes and pastry, which can make you feel hungry even after dinner. The drive does not originate from a an internal need, but is triggered by an external input. Another example is watching horror movies or driving in a roller coaster. This creates tension, although the internal drive may tend to avoid tension.

Research has revealed a larger role for motivations than initially expected. The organism will seek for positive incentives and will avoid negative incentives. For a thirsty animal, water will be a positive incentive to drink. However, it will avoid painful situations.




Hunger can be a strong motivation for acting. The body requires a continuous flow of supplies for the metabolism. If not enough food is provided, the body resorts to food reserves (e.g. fat tissue, sugar stored in the liver). When food reserves are short, the organism looks desperately for food.

“External stimuli can arouse feelings of hunger.”

External stimuli can also induce feelings of hunger. After a copious meal, there usually is some appetite for a desert. In that case there is no hunger signal of the body.
Habits and habitats can also play a role in eating behavior. If breakfast is usually at 8.30 am and when you see your watch indicating 8.30, it will stimulate your appetite. Also, people usually eat more when having dinner with friends.

The hypothalamus
Since regular meals are important for the body, the organism has several control systems to keep the blood sugar level at the proper level. The control mechanism is located in the hypothalamus. Any dysfunction of the hypothalamus will have serious consequences. People with a tumor in the hypothalamus tend to gain weight or to loose weight. The hypothalamus can be divided in two parts:

  1. The lateral hypothalamus (LH), which initiates care for a meal.
  2. The ventromedial hypothalamus (VMH), which indicates that enough food has been taken.

If the LH is damaged, an animal will not care anymore for food or water and will die. Damage of cells in the VMH will cause abundant eating, leading to obesity.


The problem
Overweight is a great health problem. Each year millions of dollars are spend on diets and other methods to loose weight. For most people diets are not successful, and those who manage to loose some weight, usually gain weight very easily again. All these problems have stimulated research to overweight.

“People use to eat more when they are stressed of anxious.”

Why eating so much?
A well-known statement about overweight is, that it is a result of emotional problems. People are thought to obtain satisfaction from food as a diversion from problems. This may seem an obvious conclusion, but research shows that most people with overweight are fully normal. People with overweight may be unhappy at some times, but their overweight is not rarely a reason for that.

The way food looks like, smells, and taste determine to a large extent how much and when we eat. Research indicates that people with overweight may more easily indulge to eating than normal people. People with overweight also pay more attention to taste and on the outlook of food.
Normal people will not eat snacks when it is almost dinner time. People with overweight more easily tend to continue.

Research has shown that people tend to eat more when they are stressed or frightened. This occurs more frequently with people with overweight than with normal people. People with overweight also tend to be less sensitive to signals from the body indicating that it has enough food.



In many animals maternal instincts determine behavior to a large extent. A mother rat, for example, will be prepared to suffer pain in order to get food for her youngsters. This is called maternal instinct. These maternal instincts are the result of hormones. This has been demonstrated by an experiment, in which blood plasma of a feeding mother rat is injected into a normal rat. The latter will then reveal the same maternal behavior. The conclusion is that maternal instincts are programmed in the brain and can be triggered by hormones.

“Maternal instincts are acquired in primates and are influenced by experiences.”

In primates maternal instincts are also learned and influenced by previous experiences. As a consequence, isolated monkeys demonstrate less maternal behavior than monkeys who grow up in groups. Also monkeys, who have their first baby reveal less maternal behavior than monkeys who have bred a larger number of babies.


The automatism to avoid pain is of vital importance for the organism. A simple incised wound can already have large consequences for the functioning of the organism if not detected and treated.

“The behavioral consequences and responses to pain are acquired during life.”

The consequences of pain and also the response to pain are learned by experience. Falling on the ground may hurt; therefore, people avoid falling.
Some pain experiences are so strong, that precautions are taken.

For example, people wear helmets when driving their bike to protect the head in case of accidents. Also people behave very carefully in situations with fire or high temperatures. The opposite also happens and alcoholic drinks give an example. When the body perceives a sensation as pleasant, it will ask for that experience again. This explains partly drug addiction.


How do we learn social rolls?
As we grow and develop in our lives, we also develop social attitudes which strongly influence our behavior. We internalize the attitudes of the society around us by making the attitudes our own. Besides attitudes, people internalize cultural expectations about how to behave. The process through which society influences individuals to internalize attitudes and expectations is called socialization. Individuals do not automatically absorb, but gradually accept cultural attitudes and roles. The individual is often unaware of his acceptance of these socially derived roles, roles are often accepted unconsciously. This is usually accomplished through the imitation of role models.

“People are playing roles; the particular role depends on the expectations from society.”

When do we act so?
When individuals “play” these roles dictated by the culture within which they live, they are sometimes conflicting with their own inner beliefs. Frequently, we may act as if we agree with our perceived social expectations, because we do not want to disappoint the people who expect us to meet a particular set of requirements. This can create an imbalance which may cause ones behavior to become illogical due to these perceived social influences.


Cognitive dissonance theory
The importance of socialization is further illustrated through Festinger’s cognitive dissonance theory. According to this theory, individuals tend to seek a consistency among their beliefs and opinions, or cognition’s. Dissonance is created by an inconsistency between attitudes or behaviors, which causes a need within the person to change in order to eliminate or lessen the dissonance. When attitudes conflict with behavior, a person is most likely to change his attitude to accommodate the behavior. To eliminate a dissonance, the person can reduce the importance of the dissonant beliefs, add more consonant beliefs that outweigh the dissonant beliefs, or change the dissonant beliefs so that they are no longer inconsistent.

“Humans strive to harmony with their fellow-man.”

For example, when those such as Megellan and Columbus began traveling the world with the new belief that the earth is round, this caused dissonance due to the prior cognition that the world is flat. Imagine yourself as a university professor who had always believed and taught his students that “the world is flat.” Now, new evidence has indisputably proven that the world is round. The dissonance can be eliminated when you accept the new knowledge over your previous belief, or when you entrench yourself in the old belief to the point that you are comfortable as a “defender” that the world is flat, because people have always taught this as the truth. By accepting that the world is round, you can reduce the importance of the dissonant belief. Looking at all that can be gained from the new proof allows you to add more consonant beliefs that outweigh the dissonant belief. However, the dissonant belief will become irrelevant when you dispute that the world is round and continue teaching that the world is flat. With either of these choices, this individual has removed the overwhelming conflict within himself that has caused imbalance, or lack of balance in his cognition of this particular belief system.


Stereotypes, or fixed characterizations, are properties of a few people or objects which are applied to a whole group. Though we often are even unaware of it, we all stereotype other people and things on a daily basis. By stereotyping others, we do so from a lack of knowledge of the entire group, making hasty generalizations about the whole due to our knowledge of only a small part.

“Often people expect stereotyped behavior.”

Some examples of common stereotypes are Americans are rude and clamorous, Englishmen are polite, and people wearing glasses are smart. Of course, these statements are not always true, for not all Americans are rude and clamorous, Englishmen are not all polite, and a person can be intelligent and not wearing glasses. However, we may sometimes learn about a group by observing a small part and making a logical stereotype. For example, we may see a large group in which half the members are carrying some sort of baseball equipment. Here, we can assume that group is possibly a baseball team. It is completely normal for us to stereotype, but it is important for us to remember that stereotypes frequently will not remain true for an entire group.


Peer pressure
We often have the tendency to adapt our behavior in order to fit in with a particular group. Peer pressure is when a person conforms to the general behavior of a group of peers in an attempt to feel more acceptable within that group. Often, we may act in ways that imitate the group or a leader of that group even though the behavior conflicts with our own cognition’s. We do so just to feel a sense of belonging to the group.

“People tend to behave like they are supposed to.”

For example, a teen living in a country where it is illegal to drink before a certain age may value the idea that it is wrong to drink anyway, yet he may hang out with other teenagers who drink at parties on weekends. If he goes to a party with these friends, it is likely that they will pressure him to drink also. This is a negative form of peer pressure.

Positive peer pressure

However, peer pressure is not always negative. A student may continuously try to convince a friend to work harder in school to make higher grades. In this case, the student is pressuring the friend in hope for a positive result for him.

The biological need for acceptance in a group can be further understood through the behavior of animals, such as birds and sheep, that tend to travel in groups. Animals do so as a survival technique, while we desire to “fit in” with accepted “norms” as a means of emotional stabilization.

Extensive research has been done on conformed behavior. One of the most famous researches has been done by Asch, in which he investigated the effects of a group on a person’s behavior, in which the subject is falsely led to believe that his perceptions are different from those of the majority. In this study, he discovered that a person’s answers to questions were guided by the opinions of the group 75% of the time, rather than by his own opinions. He also discovered that when a person has a supporter in a group, he is more likely to say what he really thinks, and is apparently under less pressure from the group.



In a previous paragraph, the difficulty in dealing with peer pressure was described. Due to this difficulty, it is usually very hard to have an independent attitude. Being independent does not mean that you never agree with the opinion of the group; it only means that when you disagree with the actions or thoughts of the group, you will discuss your opinions with them. To obtain an independent attitude, it is necessary to be self-confident.

“Being assertive means that you will enter a discussion when you disagree.”

A self-confident, independent person is far more likely to stand up for himself in a situation that conflicts with what he views as morally correct. This type of conflict, however, often results in aroused emotions, especially when the conflict deals with people who have power over you.

Biological Bases of Behavior



Nowadays nearly everyone in western countries has one or more TV-sets at home. On television often violent pictures are shown. But it is not sure whether or not violence on television results in violent behavior. Research has proven that when students leave High-School they have seen about 18,000 murders on television.

“Television can affect behavior in both positive and negative ways.”

Is it ok or is it wrong?
There are a lot of different opinions about the influence of violence on television. Some people allege that watching violence on television decreases the need for violence for the watcher himself. According to them violence on television works as a “ventilator”. So watching violence on television decreases the need of violent behavior for the watcher himself.

Others have the opinion that the watcher uses violence on television as an example for his own behavior
An inquiry between people who watched violence on television and people who didn’t, showed that the behavior of the people who watched violence on television were more aggressive than the other people.

However television can also have a positive influence on our behavior. For instance in November 1998 there was a show on the Dutch television for a collection for the victims of the hurricane Mitch. Thanks to this show more money was collected than would have been possible without this show.


 What is emotion?

The word emotion includes a wide range of observable behaviors, expressed feelings, and changes in the body state. This diversity in intended meanings of the word emotion make it hard to study. For many of us emotions are very personal states, difficult to define or to identify except in the most obvious instances. Moreover, many aspects of emotion seem unconscious to us. Even simple emotional states appear to be much more complicated than states as hunger and thirst.

“The word emotion includes a broad repertoire of perceptions, expressions of feelings and bodily changes.”

To clarify the concept of emotions, three definitions of various aspects of emotions can be distinguished:

  1. Emotion is a feeling that is private and subjective. Humans can report an extraordinary range of states, which they can feel or experience. Some reports are accompanied by obvious signs of enjoyment or distress, but often these reports have no overt indicators. In many cases, the emotions we note in ourselves seem to be blends of different states.
  2. Emotion is a state of psychological arousal an expression or display of distinctive somatic and autonomic responses. This emphasis suggests, that emotional states can be defined by particular constellations of bodily responses. Specifically, these responses involve autonomously innervated visceral organs, like the heart or stomach. This second aspect of emotion allows us to examine emotions in both animals and human beings.
  3. Emotions are actions commonly “deemed”, such as defending or attacking in response to a threat. This aspect of emotion is especially relevant to Darwin’s
  1. point of view of the functional roles of emotion. He said that emotions had an important survival role because they generated actions to dangerous situations.

These are three generally accepted aspects of behavior, but some researchers add two others aspects: motivational state and cognitive processing.


Some psychologists have tried to subdivide emotions in categories. For example Wilhelm Wundt, the great nineteenth century psychologist, offered the view that emotions consist of three basic dimensions, each one of a pair of opposite states: pleasantness/unpleasantness, tension/release and excitement/relaxation. However, this list has become more complex over time.
Plutchik suggests that there are eight basic emotions grouped in four pairs of opposites:

  1. joy/sadness
  2. acceptance/disgust
  3. anger/fear
  4. surprise/anticipation

In Plutchik’s view, all emotions are a combination of these basic emotions. This hypothesis can be summarized in a three dimensional cone with a vertical dimension reflecting emotional intensity.


There are a lot of theories about emotions, but it would be impossible to mention all of them. Therefore, we will take the most important theories.

“What happens during emotion?”

The first one is the James-Lange theory, named after William James and Carl Lange. To explain their theory we will use an example of seeing a bear.

Suppose you encounter a ferocious bear in the woods. Two things are likely to happen: (1)you run away to escape, and (2) you feel fear. The James-Lange theory postulates that you run first, then realize that you are afraid. Thus, seeing a bear leads to physiological changes such as increased blood pressure, a pounding heart and the reflex of running away. When you perceive these changes, that is, after they occur, you interpret them as an emotion (fear). In other words, emotion is the feeling of bodily changes.


See full size imageThe second theory is the Cannon-Bard theory, named after Walter Cannon and Philip Bard. The Cannon-Bard theory makes a more commonsense argument than the James-Lange theory. They postulate the following: When we see the bear, we simultaneously experience fear and the physiological state of the body changes, also in our perception. They postulated that the thalamus was the seat of emotions, and that this part of the brain regulated the physiological changes.

The third theory is called the two-factor theory. Emotional experience can be divided into two parts: general (physiological) arousal and cognitive appraisal. Arousal is the energizing aspect of emotion, and appraisal refers to recognizing, categorizing, and evaluating a situation.
Arousal signals that something is happening and if aroused, we seek an explanation for it. Depending on circumstances we label that arousal as the emotion that seems most appropriate.

The last theory we will explain is Zajonc’s theory, this theory is a variation on the two-factor theory. Zajonc doubts that cognitive appraisal as described by Schachter and Singer is the usual cause of emotional feeling. He argues that in most circumstances the emotional feeling and the behavioral reaction occur too rapidly to be caused by prior cognitive processes. Zajonc suggests instead that cognitive appraisal and emotional experience are relatively independent of each other. He argued that they proceed in parallel.


Biological value
Many of our expressions are innate. This appears from the fact that children who have been blind for all their life, make expressions like normal people. The same applies for gestures.
The famous Charles Darwin was intrigued by the expression of emotion in blind children and animals. He also proposed an evolutionary theory of emotions.

According to Darwin, many of the ways in which we express our emotions are inherited patterns that originally had a survival value. For instance, the expression of disgust is based on the organisms attempt to rid itself of something unpleasant that had been ingested.

“Most of our facial expressions are innate; however, they are being modified by experiences.”

A general meaning
Certain facial expressions seem to have a general meaning all over the world. In an experiment people from the United States, Brazil, Chile, Argentina and Japan viewed photographs of facial expressions. They had little difficulty in identifying the emotions. Even people from tribes, who had never been in contact with the western world, recognized emotional expressions on pictures without any problem. Similarly, Americans recognize without problems emotional expressions of people living in remote tribes.

Although most of our facial expressions are innate, they are modified by experience. People can learn to inhibit facial expressions, when they want to conceal feelings of anger or fear. Sometimes body cues can tell us more about a person’s emotional state (see chapter three).
Some facial expressions and gestures may be innately associated with particular emotions or attitudes, while others are learned from one’s culture. A psychologist may read a Chinese book to investigate how the writer describes the emotions of the characters. He discovered that mainly the descriptions were the same as in western books, but that there were some differences. An example of a sentence that would be misunderstood by a normal American, is the following: “Her eyes grew round and opened wide”, in the book it meant that she became angry. If you would read it, you probably think that she is astonished.

To imitate the feelings of characters, actors must try to make the correct facial expressions, tonal voice and gestures. Making the right movements by emotions makes acting very difficult.


The reason why we have chosen to explain those emotions is the fact that anger and anxiety are especially important emotions.

“Anxiety arises when the way to a goal is unclear or dangerous; anger arises when the way to a goal is blocked without an alternative.”

How do they arise?
Anxiety arises when the way to a goal is unclear or threatened; anger arises when the way to a goal is blocked, which can lead to frustration and even aggressive behavior. Anger is an emotional reaction that occurs when we blame other persons/machines for blocking us from our goals. For example, when your computer has crashed and when you have forgotten to save your work, you will be angry and frustrated. Both anxiety and anger can produce undesirable behavior.
Anxiety probably evolved to help people to cope with danger. We tend to be anxious when we think of a threatening. Anxiety has a negative incentive value, and therefore we want to escape anxiety when it occurs.

The role of motivation
Motivation is also an important factor in understanding emotions. An important experiment to investigate the role of motivation in anxiety was done by Neal Miller in 1948.
He put a rat in the white part of a two sided-box, where he got an electrical shock. This shock made him go to the second part of the box, which was painted black. This was repeated a couple of times so the rat learned that he would get a shock in the white part of the box, and in the black part he would not.
From now on, no shocks were given in any part of the box. But still the rat shows some fear when staying in the white part, and when given an opportunity, the rat would flee to the black side.
Now the white part gave him a motivation for running to the black part, because the rat experienced fear in the white part.

In a following experiment a wheel was placed in the white part of the box. By turning the wheel, the box could be opened and the rat could run to the black part of the box. It turned out that in this completely new environment, the rat wanted to flee to the black part, even when no shock was administered. The rat was not escaping for the shock now, but for his own anxiety that a shock might be delivered.
This proves that the emotion anxiety can control someone’s behavior.


What is it?


Every moment of the day your nervous system is active. It exchanges millions of signals corresponding with feeling, thoughts and actions. A simple example of how important the nervous system is in your behavior is meeting a friend.
First, the visual information of your eyes is sent to your brain by nervous cells. There the information is interpreted and translated into a signal to take action. Finally the brain sends a command to your voice or to another action system like muscles or glands. For example, you may start walking towards him.
Your nervous system enables this rapid recognition and action.

“The nervous system allows us to perceive, to interpret and to respond to events from the environment.”

The nervous system is the most complex system of the human body. The human brain itself consists of at least 10 billion neurons.
Single-cell creatures do not need a nervous system. They are in immediate contact with their environment and do not need communication between cells. Multi-celled creatures need the nervous system for the communication between their cells.

What is its function?
There are three general functions of the nervous system in man and animals:

  1. Sensing specific information about external and internal conditions (In the example above, this is seeing your friend).
  2. Intergrating that information (This is the understanding of the information coming from the eyes).
  3. Issuing commands for a response from the muscles or glands (This is the reaction of walking towards him).

The nervous system provides us the ability to perceive, understand and react to environmental events. That is why the nervous system is so extremely important for human behavior.


How is it build up?
The nervous system is able to create order out of trillions of signals it processes. This is a result of neurons linked together into tracts and bundles organized by structure and function.
The two major divisions of the human nervous system are the central nervous system (CNS) and the peripheral nervous sytem (PNS).

“What is the function of the nervous system?”

The CNS consists of the brain and the spinal cord and is primarily responsible for storing and processing information, which it receives. That information is received by nerve tracts scattered throughout the body, carrying information from and to the CNS from muscles and glands.

How does it work?
We will now give an example of the function of the nervous system in a certain situation (source: Psychology, behavior in context; modified from the original):
“A firefighter is driving home on a highway when he notices a smashed car flipped over on the side of the road. His eyes are stimulated first, triggering recognition of the damaged car, a driver trapped inside the vehicle, and smoke coming out of the engine. He formulates a plan, which is translated into neural signals enabling him to take action-to stop, run to the smoking car, and pull the dazed driver out of the car before it explodes in a burst of flames. All of this takes place over the course of a few seconds, probably without conscious awareness.”

In the story above, there is a constant communication between the CNS and the PNS. When the firefighter sees the car, his eyes send a signal via the PNS to the CNS. The CNS decides to take action. Therefore, signals are sent from the CNS to the PNS, which make it doing the things described above.
In your daily life the same happens. Think about all the sources that provide you information (like sounds and lights), and the great variety of responses to them. This is all a result of a coöperation of the PNS with the CNS, together called the nervous sytem.


Somatic and autonomous
The peripheral nervous system (from now on called PNS) has sensory neurons that carry information about the body and the environment to the CNS and motor neurons that convert the decisions of the CNS into action. The PNS is subdivided further into the somatic nervous system and the autonomous nervous system.

“The pheripheral nervous system includes neurones, which are directly involved in the processing of information from muscles and sense-organs.”

The somatic part of the PNS consists of nerves that mainly serve voluntary muscles, like your arms muscles and your vocal chords. These muscles execute the commands of the CNS.
The autonomic nervous system serves the heart, lungs, bladder, tear glands and other involuntary muscles and glands that operate instinctively without intentional control.

Sympathetic and parasympathetic
The autonomous nervous system has also two subdivisions, the sympatic nervous system and the parasympatic nervous system. Each part of the body and each organ that is served by the autonomous nervous system has one set of connections with the sympatic and one set of connections with the parasympatic division.
These two sets of connections have an opposite effect on a muscle or an organ. For example, the parasympatic system causes constriction of the pupils of the eye, and the sympatic system causes dilation of the pupils. These changes happen automatically, without intention. Some drugs can influence these changes by stimulating one of the two systems. For example, when stimulating the sympatic system, the pupils will dilate.

The autonomic nervous system underlies much of the body’s automatic response to stress and emotion. This is the reason that, when you are scared, you get a dry mouth.


The central nervous system (the CNS) consists of the spinal cord and the brain. The spinal cord, which is protected by bones in your back, contains neurons connecting the peripheral nervous system (the PNS) to the brain.
Damage to the spinal cord can cause interruption of the signals to the brain, which can result in paralysis of the body or parts of the body.

“The brain is the center for information processing.”

The brain
The other part of the CNS is the brain, one of the most complex structures of living beings on earth. A human brain weighs about 3 pounds. In the brain there are between 10 billion and 100 billion neurons. Each neuron has about 1,000 connections with other neurons.
All of our mental and behavioral processes are mediated by activity in the brain. The brain is the center for complex human information processing, as we have explained in “organisation of the nervous sytem”.

You can consider the brain divided in three major parts that can be further divided on the basis of structure and function. In order of evolution those three parts are the hindbrain, the midbrain and the forebrain.

The hindbrain is the oldest part. Its functions are primarily to serve automatic activities like breathing. The midbrain is the smallest part of these three and has a function in emotional feelings and emotions. The forebrain is the largest part. It is involved in initiating movements and in conducting higher cognitive and mental processes like thinking and language.

Some parts of the brain in particular have attracted attention of psychologists:

  1. The brain stem; this is the part of the brain that is directly connected to the spinal cord and terminates in the thalamus and hypothalamus. Capping these structures are two cerebral hemispheres that are covered by an outer layer of neural tissue called the cerebral cortex.
  2. The cerebral cortex (see figure).
  3. The corpus callosum; this is the connection between the two hemispheres, which takes care for the communication between the two hemispheres.

To visualize the arrangement of the major structures of the brain, imagine making a fist and plunging it deep into a large mass of pizza dough and then holding your arm up with the dough completely covering your fist.
Now your fist and your wrist constitute the brain stem, the mass of dough is the cerebrum, which coordinates emotional and cognitive functions.
If you baked the dough and then divided it down to the middle, the two halves would be the hemispheres. And if you covered the mess with a layer of mozzarella cheese, the cheese would be the cerebral cortex. The cortex is responsible for higher mental processes in human beings.


The two halves of the brain are as much alike as two peas, but they are not identical. Each half controls the contralateral half of the body. So the right (left) half receives and sends information from the left (right) half of the body. There are many parts in those two halfs that have different functions. They control different skihe way they process information varies form part to part.

“The brain includes several parts, each with a specific function.”

lls and t In the cortex there are primary, secondary and associative areas of information processing. The primary sensory areas handle the incoming information from different sense receptors in the body. Each sense is processed in a different primary area, for example vision, feeling and hearing.
In the secondary cortex, the information is examined better. And in the associative cortex all the information is associated or processed together.

The lobes of the cerebral cortex each have specific information to process and are seen to perform different functions. There is no common opinion about what each part of the cortex in involved in precisely, but there are some general ideas about their function: the frontal lobes are specialized for the planning and control of movements. The occipital lobes process the primary visual information (from the eyes). The parietal lobes process primary somatosensory information (information from the skin and muscles), and the temporal lobe processes the primary auditory information (from the ears). The temporal cortex is also important for speech.

The limbic system is involved in motivation, emotion and learning.

The basial ganglia are involved in the control of movement. The thalamus relays information from the senses to the cerebral cortex. The hypothalamus controls your eating and drinking, like described in the paragraph about eating.

The midbrain or tectum structures are part of the visual and auditory system and are especially concerned with reflexes and quick reactions. The reticular formation plays a role in sleep and arousal, attention, muscle movements and various vital reflexes, such as heartbeat. The periaqueductal gray matter is involved in the feeling of pain; the substantia nigra, in muscle movement control.
The cerebellum, which is situated in the hindbrain, receives information from all the senses as well as information about individual muscular movements. The cerebellum integrates the information, comparing what the body is doing with what the brain wants it to do.

The pons appears to be important in sleep and arousal, and the medulla oblongata controls vital functions such as regulation of the cardiovascular system, respiration, and skeletal muscle tone.


Behavioral genetics is a field of research in psychology, that aims to determine heritability and to determine how much of the behavior is accounted for by genetic factors. Behavioral genetics began in England with Sir Francis Galton and his study of the inheritance of genius in families. He discovered that genius ‘runs in families’ and concluded that it is to a significant degree a heritable behavioral trait.

“Behavior is influenced both by genes and the environment.”

Since Galton a lot of people tried to prove that genetics play an important role in many aspects of behavior. Those people proved that complex behaviors related to personality, psychopathology and cognition are all influenced to some degree by genetics. They have also found that genetics alone is never enough to explain behavior, because behavior is also influenced by the enviroment.

Today, most psychologists believe that behavior reflects both genetic and environmental aspects. They try to explain variability in a trait like intelligence or height or musicality in terms of the genetic and enviromental differences among people within that population.

Every organism shares several characteristic features with his parents. For example, some babies look more like their father, others more like their mother. However, a baby can also have some characteristics which are not visible in either father or mother. The phenotype is defined as the expression of the genetic information as physical, biochemical, and physiological traits. A gene is a part of the DNA that contains the information for one specific property. The genotype is defined as the set of properties, which is coded in the full set of genes. Phenotype and genotype can be related to all qualities of an organism, but they often refer only to the property under study.

“The genotype of an organism is the genetic information; the phenotype is related to the visible properties.”

Normal cells in the body contain 23 pairs of chromosomes. The two chromosomes in a pair each contain information about the same properties, but the information can be different. Sex cells (also called gametes) do not contain pairs of chromosomes but only one part of a pair. Therefore, a sex cell contains only half of the genetic information. When a sperm cell and a egg merge, most properties of the new organism are determined. This defines for the main part the physical and biochemical properties of the organism. Another important influence on the phenotype comes from the environment. The influences of the environment are called environmental factors. Examples of such factors are light, air, moistness, injuries and diseases.

An example of an environmental effect can be seen on the skin. When both your father and mother are white, the skin of the child will always be white. However, when the child falls with the head on the floor, this may cause a scar, which is not coded in the genetic information.

The ratio in which genotype and environmental factors contribute to the physical properties of an individual, is different for everyone. Some properties are determined exclusively by genotype, others only by environmental factors. In general the genotype determines the limits and the environment determines how close these limits are approached. For example, the genes of a plant determine the maximal height (e.g. 1 meter). Only when the environmental factors are favorable, the plant will reach the height of 1 meter.




Research methods to study human behavioral genetics have mainly focussed on comparison of twins, especially identical twins. (These are twins with exactly the same genes; fraternal twins only share 50% of the genes.) This is done because they share a lot of, and sometimes all, genetic material. Some genetic material is shared by all human beings. That part of the DNA makes us humans, but some genetic material can vary between persons.

“To study the environmental influences, you have to examine the common genes that people share in relation to behavior.”

Shared genes
To study the genetic influences on behavior, you must look at the genetic material shared by people, and then compare their behavior. For a given behavioral trait, like musicality, one has to examine whether the trait is present in identical twins.
But for examining the genetic influence, you must have twins who were separated shortly after birth. Only then are the environmental influences sufficiently different to be able to distinguish genetic and environmental factors.

It is important to realize that twin research is based correlation. Thus, a high correlation only suggests a genetic contribution, it cannot definitely prove it. To prove a genetic contribution, we need a way to control the environmental influences.
Twin animals can be separated at birth such that they can be compared after growing up in different circumstances. But with human beings, separating twins in order to conduct experiments, is ethically prohibited.

When human twins have been separated legally (for example, by death of their parents), their similarities and differences can be studied. But even then, causal conclusions can be difficult, because numerous cultural stereotypes are attached to physical features such as hair color, eye color and weight. Identical twins might be treated similarly, and so they might behave alike by a non-genetic factors.


We already told you a lot about genes and research on genetic influences, but we still did not tell you what those influences exactly are. To indicate the importance of genetics we will use the example of intelligence. We will explain it on the basis of investigations.

“The correlation in IQ’s seems to be higher the more genes people have in common.”

There have been a lot of studies about the relation of heredity and genes to intelligence. One of the most famous publications was published in 1981 by Bouchard and McGue. They have examined 111 studies that analyzed almost 250,000 cases.

The pattern of correlations they found shows that the higher the proportion of genes that people have in common, the higher the correlation in IQs (intelligence quotient). The average IQ correlation is .85 for identical twins, which suggests a large role for heredity but also a substantial contribution of the environment.

Environmental influences
There are also other ways to look at the environmental influences.
Fifty identical twins, brought up in different families, were tested as young adults on several tests of mental abilities. The correlation between pair members turned out to be 0.75. This was almost the same as the correlation measured by identical twins growing up at the same place. This result shows that there is a genetic base for intelligence.

For a genetic role in intelligence you can also examine the correspondences between parents and their children. However, the role of the environment will be larger, because parents and children lived in the same environment. For example, parents can learn children a specific way of thinking which is very effective. So these results will be less convincing than research based on identical twins which were brought up in different places.


Exocrine and endocrine
The word hormone is derived from the greek word ‘hormao’ and means -to excite or stir into action-. Hormones are chemicals secreted into the bloodstream by specialized organs and carried to other parts of the body to perform their task. Organs that secrete and manufacture hormones are known as endocrine glands. Exocrine glands such as tear glands, secrete their products outside the body. Whereas exocrine glands are also called ductal glands, endocrine glands are ductless. Endocrine glands come in a variety of sizes and are located through the whole body.

“Hormones are chemical substances which are secreted to the blood by special organs.”

Hormones are found throughout the animal kingdom and even in plants, but only the vertebrates have specialized organs to produce and to store hormones. In many cases the structure of a hormone is the same over a wide variety of animals, although its function can be different.
Some human hormones are not secreted by endocrine glands but come from sources as neurons in the hypothalamus, or cells in the digestive tract. Recently the heart has been found to produce a hormone that helps regulate the blood pressure.

Untill the beginning of the 20th century the communication within the body was exclusively attributed to the nervous sytem. However, investigaters discovered that the endocrine sytem is also important for this function. Yet, the role of endocrine glands was anticipated in several ancient civilizations in which they were eaten to modify health or behavior.

In the fourth century B.C. Aristoteles described the effects of behavior in birds when removing the testes (castration). Although he did not what mechanism was involved, it was clear to him that the testes were important for the male characteristics. Nowadays we know that the testes produce a certain hormone (testosteron) that cause a lower voice and stronger muscles in male human beings.


“Although hormones may be different, they have some common properties.”

Although there are a lot of different hormones with different properties, there are some general principles of hormone action. There are ten general principles:

  1. Hormones frequently act in a gradual fashion, activating behavioral and physiological responses long after the concentration of hormone in the blood has fallen. This slowness makes it quite difficult to investigate whether a behavioral change is caused by a hormone or not.
  2. When hormones alter behavior they act by changing the intensity of evoked behavior, rather then by switching a certain behavior on or off.
  3. The quantities and types of hormones are regulated by both environmental factors and endogenous factors. The relation between hormones and behavior is reciprocal. The hormone changes behavior and behavior changes the concentration of hormones in the blood.
  4. Each hormone has multiple effects on organs and behaviors, and a certain behavior can be caused by more than one hormone.
  5. Hormones are produced in small amounts and are often secreted by bursts. This way of secreting can be crucial for a small amount of hormone to be effective.
  6. The levels of many hormones vary rhythmically throughout the day.
  7. Hormones affect metabolic processes in most cells, so hormones can trigger long-term metabolic changes.
  8. Hormones interact: the effect of a hormone can be changed by another hormone.
  9. The chemical structure of hormones in all vertebrates is similar, but their functions can vary across species.
  10. Hormones can affect only those cells that possess a receptor protein that recognizes the hormone and alters cell function. Among vertebrates, the same brain region often possesses the same hormone receptors.

In this paragraph we will explain some of the human glands and we will mention the functions of a specific hormone (remember that a hormone can have more functions).

“Hormones can have a great effect on behavior.”

The first gland is the pituitary gland, also called hypophysis. It is situated in a depression in the base of the skull. It consists of two main parts: the anterior pituitary and the posterior pituitary.
The posterior pituitary contains two pricipal hormones: oxytocin and arginine vasopressin. These are synthetisized by neurons. The function of oxytocin is to stimulate the contraction of uterine muscles and it stimulates the release of milk by mammary glands.
The anterior pituitary gland secretes 6 hormones. The most important ones are Luteinizing Hormone (LH), follical stimulating hormone (FSH), prolactin and growth hormone (GH). LH stimulates the release of eggs from the ovary in females. In males LH stimulates the secretion of testosteron. FSH stimulates the secretion of testosteron in man, and estrogen hormones in females. Prolactin stimulates the development for lactation in females such that they start producing crop milk. GH effects the growth of cells by affecting metabolism.

A gland present in females only are the ovaries. Their function is to release mature gametes and to secrete hormones. The production of hormones occurs in cycles. In human beings that cycle is four weeks. The most important hormones the ovaries produce are estradiol and progesterone. The release of these hormones is controlled by the anterior pituitary. The release of FSH and LH induce the ovaries to produce the hormones.

Only males have testes, whose function is to produce sperm and to secrete hormones. The most important hormone the testes produce is testosterone. This is regulated by LH from the anterior pituitary. Testosterone controls a wide range of bodily changes that become visible at puberty, including changes in voice and hair growth.

The last gland we handle is the pancreas, and is located a little below the stomach. The pancreas not only produces enzymes, but also hormones. Important hormones secreted by the pancreas are insulin and glucagon. One of the actions of insulin is to increase the glucose uptake. People missing the hormone insulin are called diabetics. Glucagon has the opposite effect.


In this paragraph we will explain the influences of hormones on behavior. We will do this with an example on learning and intelligence.

“Hormones can also have affect on learning and thinking.”

Hormones affect both the early development of capacities to learn and remember, and their efficient use. Some hormones are important in the development of the nervous system. Insufficient amounts of that hormone lead to cretinism, because the neurons cannot develop optimally.
The ability to learn and remember can also be affected by hormones by the hormones of the hypothalamus, but the exact working of those hormones (i.a. oxytocin) is not known yet.

Both deficient and excessive hormone secretion are associated with behavioral disorders. Some of these disorders have long been known, especially those who include marked behavioral changes. For example, parathyroid deficiency results in a system portrait that resembles a psychotic state, schizophrenia.

Another example is the excessive release of the hormone thyroid. The result of this is that people appear intensely anxious. Excessive release of glucocorticoids is accompanied by many bodily and psychological changes including fatigue and depression, even intense psychotic behavior can be a result of excessive glucocorticoids.


Circadian rhythms
Most functions of any living system display an approximately 24-hour rhythm. Because these rhythms last about a day, they are called circadian rhythms. This word is derived from the latin words for about (circa) and the word for day (dies).

“Humans and other organisms live according to rhythms that are defined by the body.”

A way to study biological rhythms is to investigate a rodent, walking in a wheel. Computers are used to measure when the rodent is walking in the wheel, and on the basis of these measurements you can see when the rodent is active.
The results of an experiment with a hamster are shown in the picture. Like most rodents, hamsters are nocturnal, contrary to human beings who are diurnal. A remarkable thing is that although all psychological measures (hormone levels, body temperature) vary across the day, the carcadian show extraordinary precision. For human beings, this would not be so remarkable, because we have watches. However, also animals are attending to a ‘biological clock’.

If a hamster is blinded or placed in a dark environment, it continues to show a daily rhythm in wheel running, despite the absence of light and dark. This suggests that animals have an internal clock to regulate their activities. However, when blinded the hamster shows a bit of imprecision in its cycle; each day he starts a few minutes later with its activities. That is why scientists now think that his internal cycle is a bit longer then 24 hours. You can see this in the picture, when there is no light and dark difference. He will start each day a bit later with his wheel running.

Normally our internal clock is reset by light. If we expose a nocturnal animal to periodic light and dark, he will soon adapt his wheel running to the dark period.
In humans, circadian rhythms are also entrained by social stimuli. And when you should do the same experiment as done with a hamster with a human, he will reveal the same characteristics. In humans the internal clock cycle is also a bit longer than 24 hours.


Sleep seems to be characterized by the absence of behavior, a period of inactivity. In the early 1960s experimenters found that you could measure brain activity during the sleep by using electrodes on the human scalp. This allowed them to classify levels of arousal and states of sleep. This method revealed two main classes of sleep: the slow-wave sleep and the rapid eye movement sleep, also called REM sleep. They also discovered that there are five stages of sleep.

“Some people sleep long, others hardly need any sleep. This varies from person to person.”

There has been a lot of research about sleep. Whole laboratories were arranged as bedrooms with a lot of sensors. By doing all that research experimenters discovered that young adults usually sleep seven to eight hours. Forty-five to fifty percent of their sleep is stage 2 sleep, and twenty-five percent is REM sleep.
A typical night of an adult shows repeating cycles of about 90 to 110 minutes long (see graph). You can see in this graph that the REM sleep is more prominent in the last cycles of the sleep.

The amount of sleep
The portrait of sleep in man shows many variations. Some differences can be clearly related to maturational status, functional states like stress, drugs, and many other external and internal states.
Some people sleep long, and others hardly sleep at all. This varies from person to person.
There is a case known of a woman who only slept one hour a day. She was a busy person who could easily fill her 23 hours of daily wakefulness. During the night she sat on her bed reading or writing. She was tested in an experiment, and for the first two days in the laboratory she did not sleep. Later her sleeping behavior was recorded for five days and she slept with an average of 67 minutes a day, and she did not even complain about tiredness or that she wanted to sleep more!
There turned out to be a heredital factor in sleeping a little. Many of the examined persons who slept a little had parents who did the same.


There are advertisements in the newspapers about people who state that they have discovered a way to learn while sleeping. Most of the time these people are just impostors. But is there a scientific evidence for learning while sleeping?

“Learning during your sleep is not possible yet, although is might be possible in the future.”

Several nonhuman experiments indicate that simple conditioned responses can be acquired during various sleep stages. But evidence of people learning verbal materials while asleep are modest. Studies about sleeping people provided no convincing evidence that those people could recall materials when they were awake.

Until recently all such experiments used explicit recall of recognition. The test person was asked to recall or to recognize some material. Investigators of learning now differentiate this from implicit memory; this means the subjects reveal memory through their performance. A type of implicit memory is seen in priming, where recent use of a specific word makes it more likely that the subject will offer that word in a response.
There was an investigation about the memory of words in which test persons heard words in their sleep. Later when the researchers asked them for the words, those who heard the word in their sleep could not remember that word, neither explicitly or implicitly.
This suggests that learning during the sleep is not possible.

Some less complicated forms of learning are possible in both humans and other animals. By use of EEG, which measures brain activity, it can be investigated whether there is brain activity when you try to learn something while sleeping.
For example, if a loud sound is presented during sleep, the subject will show EEG signs, which decreases during repetition of the stimulus. This phenomenon indicates that the novelty of a stimulus can be detected in the sleeping state; so in theory, a certain way of learning should be possible.

Another way of remembering things is the remembering of dreams. This is also a sign that you can learn while sleeping. Because you are always sleeping when you are dreaming, and nevertheless you can often remember dreams.
Although learning while sleeping is not possible yet, it might be possible in the future.

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~ by mkthlndumol on May 8, 2009.

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