BY ELLIE ZOLFAGHARIFARD FOR MAILONLINE
"Experts believe altruistic people have a different brain structure compared to those who are selfish.
In particular, the part of the brain most commonly associated with emotions is larger in selfless people, which helps them recognise the needs of others more accurately.
The study was inspired by a kidney donor called Harold Mintz, who anonymously donated his organ to a stranger, without payment a decade ago.
This was, according to lead author Professor Abigail Marsh, an act of 'extraordinary' kindness – and now a study has revealed Mr Mintz' brain structure, rather than experience, played a key role in his decision.
To test her theory, Professor Marsh of Georgetown College scanned the brains of 19 altruistic kidney donors.
Researchers used MRI scans to record the neural activity of the kidney donors, as well as 20 other people who had never donated an organ.
'The results of brain scans and behavioural testing suggests that these donors have some structural and functional brain differences that may make them more sensitive, on average, to other people's distress,' Professor Marsh explained.
During the scans, each participant looked at faces with fearful, angry or neutral expressions.
In the right amygdala, a region of the brain linked with emotions, altruists displayed greater brain activity while viewing fearful expressions than their control subjects.
When asked to identify the emotional expressions presented in the face images, altruists recognised fearful facial expressions relatively more accurately than the other volunteers.
'The brain scans revealed that the right amygdala volume of altruists is larger than that of non-altruists,' Professor Marsh said.
'The findings suggest that individual differences in altruism may have an underlying neural basis.'
These findings dovetail with previous research by Professor Marsh that found structural and functional brain differences appear to make psychopaths less sensitive to others' fear and distress.
These differences include amygdalas that are smaller and less responsive to fearful expressions.
People who are unusually altruistic could be the opposite in some ways from people who are psychopathic, she concluded."