Personality is partly determined by the shape of our brains, a new study has found.
In neurotic people prone to mood changes and psychiatric disorders, the outer layer of the brain is thicker and less wrinkly, according to the research.
Individuals with "open" personalities linked to curiosity and creativity show an opposite pattern.
The outer layer, or cortex, of their brains is thinner and more folded in certain regions with a greater surface area.
Psychologists break down human personality into the "big five" traits - neuroticism, openness, extraversion (which determines a person's level of enthusiasm), agreeableness (a measure of altruism), and conscientiousness (a measure of self-control).
The new findings show personality might be the result of the brain's general structure as well as its circuitry.
More than 500 volunteers took part in the international study and had brain imaging scans.
Researchers focused on the anatomy of the cortex, where the higher functions that make us human are centred.
Dr Luca Passamonti, a member of the British, US and Italian team from Cambridge University, said: "Evolution has shaped our brain anatomy in a way that maximises its area and folding at the expense of reduced thickness of the cortex.
"It's like stretching and folding a rubber sheet - this increases the surface area, but at the same time the sheet itself becomes thinner. We refer to this as the 'cortical stretching hypothesis'."
Cortical stretching has allowed the human brain to expand rapidly without becoming too big for our skulls.
The process was said to begin in the womb and continue throughout childhood and adolescence into adulthood.
At the same time, neuroticism decreases as we get older and we become better at handling emotions.
In contrast, the traits of conscientiousness and agreeableness grow more pronounced with age.
As a result, people tend to become more responsible and less antagonistic as they get older.
