The shape of our brain can provide surprising clues about how we behave -- and about our risk of developing mental health disorders -- suggests a new study.

An international team of researchers from the UK, US, and Italy analyzed a brain imaging dataset from over 500 individuals made publicly available by the Human Connectome Project, a major U.S. initiative funded by the National Institutes of Health.

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In particular, researchers looked at differences in the brain cortical anatomy (the structure of the outer layer of the brain) as indexed by three measures -- the thickness, area and amount of folding in the cortex -- and how these measures relate to the Big Five personality traits.

These Big Five personality traits are neuroticism (how moody a person is); extraversion (how enthusiastic a person is); openness (how open-minded a person is); agreeableness (a measure of altruism) and conscientiousness (a measure of self-control).

"Evolution has shaped our brain anatomy in a way that maximizes its area and folding at the expense of reduced thickness of the cortex," said Dr Luca Passamonti from the Department of Clinical Neurosciences at the University of Cambridge.

"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 is a key evolutionary mechanism that enabled human brains to expand rapidly while still fitting into our skulls, which grew at a slower rate than the brain.

 "Interestingly, this same process occurs as we develop and grow in the womb and throughout childhood, adolescence, and into adulthood: the thickness of the cortex tends to decrease while the area and folding increase," said Professor Antonio Terracciano from the Department of Geriatrics at the Florida State University.

As we get older, neuroticism decreases and we become better at handling emotions. At the same time, conscientiousness and agreeableness increase and we become progressively more responsible and less antagonistic.

Researchers found that high levels of neuroticism, which may predispose people to develop neuropsychiatric disorders, were associated with increased thickness, as well as reduced area and folding in some regions of the cortex such as the prefrontal-temporal cortices at the front of the brain.

In contrast, openness, which is a personality trait linked with curiosity, creativity and a preference for variety and novelty, was associated with the opposite pattern, which is reduced thickness and an increase in area and folding in some prefrontal cortices.

"Our work supports the notion that personality is, to some degree, associated with brain maturation, a developmental process that is strongly influenced by genetic factors," said Dr. Roberta Riccelli from Italy.

People are continually shaped by their experiences and environment, but the research revealed clear differences in brain structure linked with differences in personality traits that suggest there will almost certainly be an element of genetics involved.

"This is also in keeping with the notion that differences in personality traits can be detected early on during development, for example in toddlers or infants," according to Professor Nicola Toschi from the University 'Tor Vergata' in Rome.

The volunteers whose brains were imaged as part of the Human Connectome Project were all healthy individuals aged between 22 and 36 years with no history of neuro-psychiatric or other major medical problems.

The relationship between differences in brain structure and personality traits in these people suggests that the differences may be even more pronounced in people who are more likely to experience neuro-psychiatric illnesses.

This study has been published in the journal Social Cognitive and Affective Neuroscience.

Tagsbrain shape, mental health disorders, brain cortical anatomy, Big Five personality traits, neuroticism, extraversion, openness, agreeableness, conscientiousness