full story and photos:
The primates have an
altruistic 'tally chart' that keeps track of social rewards and gifts.
23 December 2012
Monkeys might not be known for their generosity, but when they do
seem to act selflessly, a specific area in their brains keeps track
of these kindnesses.
The discovery of this neuronal tally chart
may help scientists to understand the neural mechanisms underlying
normal social behaviour in primates and humans, and might even
provide insight into disorders such as autism, in which social
processing is disrupted.
Steve Chang and his colleagues from
Duke University in Durham, North Carolina, used electrodes to
directly record neuronal activity in three areas of the brain
prefrontal cortex that are known to be involved in social
decision-making, while monkeys performed reward-related tasks.
When given the
option either to drink juice from a tube themselves or to give the
juice away to a neighbour, the test monkeys would mostly keep the
drink. But when the choice was between giving the juice to the
neighbour or neither monkey receiving it, the choosing monkey would
frequently opt to give the drink to the other monkey.
The researchers found that in two out of the three brain areas
being recorded, neurons fired in the presence or absence of the
juice reward only. By contrast, the third area -- known as the
anterior cingulate gyrus -- responded only when the monkey allocated
the juice to the neighbour and observed it being received. The
authors suggest the neurons in the ACG respond to and record the act
simultaneously. The study's results are published today in Nature
'This is the first time that
we have had quite such a complete picture of the neuronal activity
underlying a key aspect of social cognition. It is definitely a
major achievement,' says Matthew Rushworth, a neuroscientist at the
University of Oxford, UK.
The anterior cingulate gyrus is
known to be a region that is specialized for social decision-making
in primates, and it is located in the same area of the brain as that
associated with the generation of feelings of empathy in humans.
'The great complexity of
human social interactions and the huge variation in what we find
rewarding compared with other primates prompts questions about
whether the anterior cingulate
gyrus operates similarly in the human brain,' Matthew Apps and
Narender Ramnani, who work on neuroimaging and human cognition at
Royal Holloway, University of London, UK, told Nature in an email.
Through the development of a specific part of the brain that
experiences the reward of others, social decisions and empathy-like
processes may have been favoured during evolution in primates to
allow altruistic behaviour. 'This may have evolved originally to
promote being nice to family, since they share genes,
and later friends, for reciprocal benefits,' says Michael Platt,
a neuroscientist from Duke University who is a co-author of the
The authors suggest that the intricate balance between
signalling of neurons in these three brain regions may be crucial
for normal social behaviour in humans, and that disruption may
contribute to various psychiatric conditions, including autistic