Microbiota, pollutants, life experiences... How is our personality built?

Why do some children seem naturally cheerful, while others appear anxious or angry from birth? How are extroversion, creativity, or professionalism formed? Science is beginning to decipher the complex mechanisms that shape our individuality. In his book "The Biology of Personality" (Odile Jacob), Professor Bernard Sablonnière, physician, biologist, and researcher at Inserm, explores these processes by explaining that our thoughts, reactions, and behaviors are based on material foundations that biology is gradually shedding light on.

Temperament and character, the cements of personality

From birth, every child exhibits a unique temperament. Some babies are calm, others more agitated or anxious. "This temperament, shaped by our genes and the neural connections established before birth, constitutes the innate part of our personality and remains relatively stable over time: it is difficult to change or manipulate."

But personality isn't just about what we inherit at birth. " Character, on the other hand, is built gradually through experiences, relationships, education, habits, and our environment. For example, a child who is naturally reserved can become more outgoing and sociable if they grow up in a supportive and warm environment," he continues. "Thus, temperament and character combine to forge personality, which is a set of psychological traits specific to a person, distinguishing them from others."

The brain, conductor of personality

The brain plays a central role in shaping our personality. Two main mechanisms are at work: the organization of neural networks and the action of neurotransmitters, the chemicals that allow neurons to communicate with each other. " The complex balance between these chemical messengers (dopamine, serotonin, etc.) shapes the traits specific to each individual, depending on their sensitivity." To better understand this diversity, psychologists often use the "Big Five" model (see box), which groups personality into five major fundamental traits.

A constantly evolving identity

While temperament provides a foundation, personality evolves thanks to the brain's plasticity—its ability to adapt and change. This process is particularly intense during childhood and adolescence, when the brain continues to develop until about age 25. " But even in adulthood, significant events, such as bereavement, illness, or a life change, can alter certain aspects of our character."

Microbiota and pollutants: unexpected influences

Professor Sablonnière also highlights the importance of the gut microbiota and environmental pollutants in shaping our personality. The microbiota, often called the "second brain," constantly communicates with our nervous system, influencing our mood, stress levels, and certain personality traits. " An unbalanced diet or excessive use of antibiotics can disrupt this balance and weaken our psychological well-being."

For their part, pollutants such as pesticides, heavy metals, or endocrine disruptors can interfere very early, as early as the brain is forming in the fetus. They are capable of altering the development of neural networks and influencing brain function from birth. " Recent studies show that exposure to these chemical substances can promote, in children, behaviors marked by high extroversion, high energy, but also difficulty maintaining attention during tasks requiring concentration."

The harmful role of social networks in self-construction

During adolescence, a period of great cerebral malleability, external influences are decisive. " Social networks, in particular, play a major role in the construction of young people's identities. They offer spaces for expression and recognition, but also expose them to comparison, social pressure, and cyberbullying."

Likes and comments activate reward circuits, sometimes reinforcing certain traits such as extroversion or narcissism. " This quest for validation can also undermine self-esteem and increase anxiety, especially in adolescents whose personalities are still developing."

Personality in action thanks to MRI

Among the major advances in neuroscience, magnetic resonance imaging (MRI) has revolutionized the understanding of personality. This technology " offers a unique window into the living brain and helps us understand how major personality traits are structured," explains Professor Bernard Sablonnière. Functional MRI has made it possible to identify specific networks associated with extroversion, openness to experience, and agreeableness. In high-potential individuals or "genius brains," MRI reveals a remarkable density of connections in certain areas of the brain, particularly the prefrontal cortex.

The "Big Five"

Psychology distinguishes five major personality traits, called the "Big Five," which are closely linked to how our brain functions.

Openness to experience describes people who are curious, creative, and open to new things. This taste for exploration is linked to dopamine, a neurotransmitter associated with desire.

Conscientiousness characterizes organized and reliable individuals, thanks to specific connections between their prefrontal cortex and other brain areas.

Extroversion , also influenced by dopamine, concerns people who are sociable, enthusiastic and attracted to interactions.

Agreeableness reflects kindness, empathy, and warmth, supported by activation of the insula, a region involved in social emotions.

Finally, neuroticism, linked to variations in serotonin, results in a tendency towards anxiety and sadness.