Researchers find almond-shaped clump of nerves in brain is larger in
more gregarious people
Ian Sample, Science correspondent
guardian.co. uk, Sunday 26 December 2010 18.00 GMT
An almond-shaped group of nerves at the base of the brain may be
the reason why some people can deal with a varied social life.
Photograph: David Job/Getty Images
If your social life is a blur of friends and family, you might want
to thank an almond-shaped clump of nerves at the base of your brain.
Researchers have found that part of the brain called the amygdala, a
word derived from the Greek for almond, is larger in more sociable
people than in those who lead less gregarious lives.
The finding, which held for men and women of all ages, is the first
to show a link between the size of a specific brain region and the
number and complexity of a person's relationships.
The amygdala is small in comparison with many other brain regions but
is thought to play a central role in coordinating our ability to size
people up, remember names and faces, and handle a range of social
Researchers at Massachusetts general hospital in Boston used magnetic
resonance imaging (MRI) scans to measure the amygdalas of 58 people
aged 19 to 83 and found the structure ranged in size from about 2.5
cubic millimetres to more than twice that.
As part of the study, each of the volunteers completed a
questionnaire giving the number of people they met on a regular
basis. They also commented on the complexity of each relationship.
For example, one friend might also be a boss, meaning the person had
to adapt their behaviour with the person depending on the nature of
The team, led by psychologist Lisa Feldman Barrett, found that
participants with larger amygdalas typically had more people in their
social lives and maintained more complex relationships.
Those with the smallest amygdalas listed fewer than five to 15 people
as regular contacts, while those with the largest amygdalas counted
up to 50 acquaintances in their social lives. Older volunteers tended
to have smaller amygdalas and fewer people in their social group.
Writing in the journal, Nature Neuroscience, Barrett's team cautions
that the finding is only a correlation, meaning they cannot say
whether there is a causal link between the size of the amygdala and
the richness of a person's social life. However, previous studies
with primates show that those that live in large social groups also
have bigger amygdalas. "People who have large amygdalas may have the
raw material needed to maintain larger and more complex social
networks," said Barrett . "That said, the brain is a use it or lose
it organ. It may be that when people interact more their amygdalas
get larger. That would be my guess.
"It's not that someone with a larger amygdala can do things that
someone with a smaller amygdala cannot do. People differ in how well
they remember people's names and faces and the situation in which
they met them. Someone with a larger amygdala might simply be better
at remembering those details," Barrett added.
Previous studies have found that parts of the brain enlarge to cope
with more demanding tasks. In 2000, a team of neuroscientists led by
Eleanor Maguire at UCL showed that in London taxi drivers, part of
the brain called the hippocampus grows to help them remember a mental
map of the city.
Barrett's MRI scans revealed no other brain structures that varied in
size according to the extent and complexity of a person's social life.
The work builds on previous research by Robin Dunbar, director of
social and cultural anthropology at Oxford University, who found a
theoretical limit to the number of meaningful relationships a person
can maintain. The figure is rough but considered to be about 150.
Barrett did not look at whether amygdala size varied with the number
of contacts a person had on social networking websites like Facebook
or Twitter, in part because it is unclear whether these require the
same cognitive effort to maintain as more traditional relationships.
Barrett's group is now looking at other brain regions to see which
others are involved in social behaviour, and how abnormalities or
injuries to the brain can impair a person's social life.