Brain shape can predict personality traits and risk of mental health problems, new research suggests.

An international team of scientists analyzed more than 500 scans of brains belonging to adults between the the ages of 22 and 35, collected as part of the Human Connectome Project. Study participants had no reported history of neuro-psychiatric or other major medical problems. As part of the project each of the participants underwent a series of personality tests.

Researchers compared three brain characteristics -- thickness, area, and amount of folding in the cortex -- to five major personality traits, including neuroticism, extraversion, openness, agreeableness and conscientiousness.

"Evolution has shaped our brain anatomy in a way that maximizes its area and folding by reducing thickness of the cortex," Luca Passamonti, a neuroscientist at the University of Cambridge, explained in a news release. "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 and folding allowed humans to develop more powerful brains without growing massive skulls.

"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," said Antonio Terracciano, an associate professor of geriatrics at Florida State Univeristy. "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."

Cortical stretching has many psychological benefits. Previous studies have shown humans, as they age and their cortex stretches and folds, become less neurotic and better able to handle emotions. They also become more agreeable and conscientious, better able to get along with others and exercise self-control.

The latest analysis revealed a link between increased levels of neuroticism -- a risk factor for neuro-psychiatric problems -- and increased thickness, reduced surface area and a lack of folding among some prefrontal cortices. Conversely, researchers found prefrontal cortical thinness, increased area and increased folding were linked to openness, or open-mindedness -- a personality trait correlated with creativity and curiosity.

Researchers published their findings in the journal Social Cognitive and Affective Neuroscience.

"Linking how brain structure is related to basic personality traits is a crucial step to improving our understanding of the link between the brain morphology and particular mood, cognitive or behavioral disorders," Passamonti said. "We also need to have a better understanding of the relation between brain structure and function in healthy people to figure out what is different in people with neurological and psychiatric disorders."