The same part of the brain that makes us crave food and sex may also help determine whether somebody is a warm and sentimental "people" person, researchers said on Wednesday.
Scientists found a greater concentration of brain tissue in certain areas of the brain may drive some people to gush fuzzy feelings more than others, they reported in the European Journal of Neuroscience.
"It is interesting that we can pin down this relationship between a specific aspect of your personality and a specific region of the brain," Graham Murray of Cambridge University in Britain, who led the study, said in a telephone interview.
"Those are the regions that we know are important for basic biological drives like for food and sex."
The researchers, who collaborated with a team at Oulu University in Finland, used questionnaires to help measure the relationship between personality and brain structure in 41 men.
The volunteers were asked how well they thought they connected to people, how they showed their emotions and whether they liked to please people.
More brain tissue
The researchers used brain scans to analyse the concentration of grey matter - tissue rich in brain cells known as neurons - in different regions.
People who scored "warm and fuzzy" on the questionnaires had more brain tissue in the orbitofrontal cortex - the outer strip of the brain just above the eyes - and in a deep structure in the centre of the brain called the ventrial striatum, the study found.
Previous research showed the two areas were important for how the brain processed certain pleasures such as sweet tastes or sexual stimuli, the researchers said.
"Sociability and emotional warmth are very complex features of our personality," Murray said.
"This research helps us understand at a biological level why people differ in the degrees to which we express those traits."
Cultural differences could also play a role, Murray said, and gave the example that Americans tended to score higher on personality tests than Scandinavians.
He said the new findings could offer clues into how the human brain evolved and offer insights into psychiatric disorders marked by problems with social interaction like autism or schizophrenia.
"Maybe the brain structure that supports social interaction evolved out of the brain structures that supported basic survival drives," he said.
"It opens a line of enquiry to investigate some of these problems that psychiatric patients may have." - (Michael Kahn/Reuters, May 2009)
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