Brain cells recognise whole face, not parts

"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 insight.

"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 individuals."

The findings could pave the way for better understanding of a variety of psychiatric diseases such as mood disorders and autism.