You probably know people who are bursting with energy and liveliness, while others are very reserved and cautious. Such behavioral patterns are not limited to specific situations, but are present throughout a person's life. Even in young children, you can observe how different they tend to be. Each person has their own way of reacting to their environment, expressing their feelings, and relating to others. This phenomenon can be seen in animals such as dogs and cats as well.

The mystery of human diversity

Since ancient times, humanity has wondered about the differences between individuals and tried to explain them. Why are some people quick to anger, while others tend to be calm and dreamy? The desire to understand individual differences is as old as humanity itself. The ancient civilizations had already developed sophisticated systems for categorizing personalities.

In ancient China, the philosophy of Yin and Yang, coupled with the theory of the five elements, already provided a conceptual framework for explaining variations in temperament. At the same time, in India, the Ayurvedic system proposed a classification of individuals into three constitutional types, Vata, Pitta, and Kapha, each associated with specific personality traits. These holistic approaches, linking the human microcosm to the universal macrocosm, demonstrated a deep intuition about the interconnectedness of body, mind, and environment.

Ancient Western conceptions

Greek philosophers and physicians, such as Hippocrates and Galen, wrote about the human temperaments, linking human behavior to bodily humors. Their theory identified four main temperaments:

• sanguine: cheerful, carefree, optimistic, curious
• melancholic: quiet, pessimistic, thoughtful, passive
• phlegmatic: calm, patient, reliable, rational
• choleric: energetic, restless, aggressive, impulsive

Medieval scholars, inheriting ancient knowledge enriched by contributions from Arabic and Persian science, developed complex treatises on temperaments.

These classifications aimed to understand and predict individuals' reactions and dispositions in response to life situations. Although these ideas seem simplistic today, they laid the foundations for modern personality psychology.

The constitutional basis of personality

In psychology, the term “temperament” refers to strongly hereditary personality traits that persist over time. These innate traits represent the biological and instinctive dimension of the personality. It is the aspect of the personality that manifests itself first.

According to the Polish psychologist Jan Strelau, the temperament has the following characteristics:

• Biologically determined: It is largely inherited and linked to our central nervous system.
• Visible since childhood: It manifests itself very early in life, before significant cultural or social influences have had time to shape personality traits.
• Stable over time: Temperament traits remain relatively stable throughout life, although they may be expressed differently depending on the situation.
• Not situation-specific: It manifests itself in a variety of contexts and influences how we respond to stimuli.
• Independent of learning: Although the environment can modulate the expression of temperament, its basic traits are considered innate.

These characteristics mainly influence the formal aspects of behavior, such as its intensity, speed, and responsiveness to stimuli.

A neurobiological explanation

The reticular formation, which consists of a network of neurons, is located in the brainstem. In its ascending function, it plays an important role regarding the temperament:

• It filters sensory information by reducing repetitive sensory impulses and allowing only important impulses to pass through, thus preventing information overload. This is probably why you may have not noticed the noise made by your computer's fan until you read this sentence. As the noise was constant, it was filtered out.
• In its motor function, the reticular formation is involved in maintaining muscle tone and coordinating the contractions of striated skeletal muscles.

The reticular formation acts as a receptacle for all sensory information, whether external or internal, and all motor activities. The more this influx activates the reticular formation, the more it has an energizing effect in return on the sensory and motor systems. It is an energy generation center in the brain that manifests itself on two levels:

• Sensory arousal puts the systems involved in internal and external perception on alert. Arousal therefore primarily lowers perception thresholds. As a result, you perceive what is happening around you more intensely.
• Motor arousal increases the willingness to act. This makes your behavior more impulsive.

An energy generating powerhouse

The temperament is one of the seven personality levels described by Professor Julius Kuhl of the University of Osnabrück in his PSI theory. According to him, it is a basic system that is primarily determined by genes and defines your level of pure inner energy. This energy can be directed outward in the form of physical actions, as well as inward at the sensory level, where it triggers sensations and thoughts. However, it does not have a specific goal. The temperament manifests itself on two different levels, sensory and motor.

Sensory temperament

One aspect of the temperament is the level of arousal in the area of perception and sensations.

• High sensory temperament: High sensory arousal involves a very low stimulation threshold and intense inner nervousness that is hardly visible from the outside. Every external input, even insignificant ones, can trigger a flood of thoughts. The person's attention is then overwhelmed by the enormous flow of feelings and thoughts. As a result, those affected are often perceived as being disconnected from the world and dreamy.
• Low sensory temperament: People with low sensory arousal find it easier to focus on signals from the outside world. However, their perception is less refined and subtle stimuli easily escape them. Their inner life is therefore less rich.

A high sensory temperament goes hand in hand with intense sensory perception and a flood of ideas. Attention is focused on sensations, feelings and thoughts. This can be inappropriate in certain situations, preventing the person from paying sufficient attention to what is happening around them. At the same time, this way of functioning has great creative potential, because it involves access to a very rich and varied inner world.

The motor temperament

The other aspect of the temperament is related to physical arousal, which manifests itself through movement and action. It influences your level of physical agitation.

• High motor arousal can manifest itself as impulsivity. If motor arousal is very high, the person may find it difficult to sit still without moving. For such a person, the prospect of spending most of their vacation lying on a deck chair is pretty awful. They need a certain amount of activity in order to rest.
• Low motor arousal can be perceived as physical inhibition. People with very low motor arousal tend to be inert and need some time before they can act.

People with high motor arousal find it very easy to get going and take action quickly. On the other hand, a low level allows one to maintain a calm and restrained demeanor.

Primary and secondary responses

Your actions, thoughts and feelings are influenced by your temperament. In a given situation, it shapes your primary response, which is triggered immediately and without any effort. According to Kuhl, the primary response is the emotional and cognitive action that manifests itself first. It is mainly determined by genes, but also depends on epigenetic factors and experiences in early childhood. This is why it is solid and difficult to change. You are, so to speak, at their mercy.

Is it possible to act against the impulses of your temperament? In principle, yes. You can develop a secondary response that allows you to act differently from how you would spontaneously. Over time, your secondary response will be triggered more and more quickly until it overshadows your primary reaction.

Developing a secondary response is a positive strategy. It allows you to respond in a flexible manner, avoiding the disadvantages of your primary response when necessary. It is therefore certainly preferable to remain calm at first, rather than physically attacking someone who upsets you. However, if your temperament is extreme, this solution has its limitations.

Key points regarding the temperament

The temperament is the most innate aspect of your personality and is largely determined by your genetic makeup. It refers to the fundamental traits that characterize you from birth until the end of your life.

According to Kuhl's particular concept, the temperament determines the pure energy that your body provides at the sensory and motor levels. A high sensory temperament causes impressions, thoughts and feelings to be more intense. These internal activities, this “noise in the head,” prevent those affected by it from paying full attention to their environment, hence their lack of attention to the outside world.

A very high motor temperament, on the other hand, prompts the person to become active and move around. In our society, a person who is constantly on the move, interrupts others and quickly becomes impatient is frowned upon. It is even worse for children in the classroom, where silence and immobility are required.

It should be kept in mind that temperament is only one of Kuhl's seven levels of the personality. Other elements of the personality can moderate it, reinforce it, or channel it in a certain direction.

Main sources:

• KUHL, Julius et QUIRIN, Markus Rainer, 2025. Persönlichkeitspsychologie : Motivation, Kognition und Selbststeuerung: ein integratives Lehrbuch. 2., vollständig überarbeitete Auflage. Göttingen : Hogrefe Verlag. ISBN 978-3-8017-3258-5. (book in German)
• French article on the reticular formation of the brain: ressources.unisciel.fr/physiologie/co/grain5_5b.html
  
  

This article was first published in French in December 2024 and has now been translated into English by the author himself.

Author of the article: Beát Edelmann, expert in neurodiversity (autism, ADHD and high IQ) and personality exploration. He is the founder of the Abundana Institute for Self-Management in Geneva, which offers coaching, training, and consulting services in French, English, and German.

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