Brain cells or neurons can recognise whole faces, not their parts,
enabling us to tell friends from strangers or a sad from a happy
"The finding really surprised us," said Ueli Rutishauser, study
co-author, neuroscientist and visitor at the biology division of
California Institute of Technology (Caltech).
"Here you have neurons that respond well to seeing pictures of
whole faces, but when you show them only parts of faces, they
actually respond less and less," said Rutishauser, the journal
Current Biology reports.
Neurons are located in the amygdala, part of the brain that
processes emotions. However, these results show that amygdala may
have a more general role in processing stimuli such as faces,
according to a Caltech statement.
Other researchers have described the amygdala's neuronal response
to faces before, but this dramatic selectivity -- which requires
the face to be whole in order to elicit a response -- is a new
"Our interpretation of this initially puzzling effect is that the
brain cares about representing the entire face, and needs to be
highly sensitive to anything wrong with the face, like a part
missing," explained Ralph Adolphs, senior study author and
professor of neuroscience at Caltech.
"This is probably an important mechanism to ensure that we do not
mistake one person for another and to help us keep track of many
The findings could pave the way for better understanding of a
variety of psychiatric diseases such as mood disorders and autism.