The features in this set of images change gradually, yet our brains flip suddenly from seeing Margaret Thatcher to seeing Marilyn Monroe.© Dr Jenny Gimpel/University College London

By transforming the features of Margaret Thatcher into those of Marilyn Monroe, researchers have revealed hints about how our brains put a name to a face.

Neuroscientists already know that certain spots in the brain play a vital role for recognizing a familiar face, even as it changes with age or a new hairstyle. But they have not been clear precisely what each area does.

Using mugshots of celebrities, Pia Rotshtein at University College London and her colleagues have shown that there are at least three separate areas for processing and recognising faces. One processes the physical features of the face, one decides whether or not the face is known, and a third retrieves information about that person, such as their name.

Rothstein's team used a computer to create a series of images in which the countenance of film star Marilyn Monroe gradually morphed into that of former British prime minister Margaret Thatcher, or that of James Bond actor Pierce Brosnan transformed into current prime minister Tony Blair.

Although the physical features gradually change from one face into another, the researchers showed that subjects looking at the images tend to "suddenly flip" from seeing Marilyn to seeing Maggie, explains team member Jon Driver.

Maggie or Marilyn?

The researchers then showed their subjects three different pairs of images from the array while they were in a functional magnetic resonance imaging (fMRI) brain scanner. The two pictures in one pair were identical; in another pair they had different physical characteristics but were both still recognizable as Maggie; and in the other pair they differed by the same degree in their physical characteristics, yet one was still recognizable as Maggie and the other as Marilyn.

The study allowed the team to pick out the three areas of the brain that carry out different tasks when someone walks into a room. The first region, a pair of structures at the back of the brain called the inferior occipital gyri, was most active when the physical features, such as eyes and hair, in the two pictures differed. It appears to analyse these physical characteristics.

A second region, the right fusiform gyrus, located just behind the ears, was most active when one picture showed Maggie and one showed Marilyn. This region appears to distinguish between faces, perhaps by comparing the face to known ones.

A third area, the anterior temporal cortex, appears to store knowledge connected to the faces. This region was most active when people knew the famous subjects particularly well; less so in those who, for example, were less familiar with the British politicians.

The study is the first to clearly show these three separate stages of face processing, says psychologist Isabel Gauthier, who studies face and object recognition at Vanderbilt University in Nashville, Tennessee.

Driver says he now wants to study patients who, through injury or disease, have particular problems recognising people. Some people with prosopagnosia, or face-blindness, may be unable to recognise faces as familiar as their own children. Patients with dementia may struggle to put a name to a household face.

Driver wants to examine whether he can match up patients' specific problems to different defects within the brain regions identified by the team. He also wants to find out whether some patients could be trained to revamp these failing regions. 

• References

  1. Rotschtein P., Henson R. N. A., Treves A., Driver J. & Dolan R. J. Nature Neuroscience, published online. doi:10.1038/nn1370 (2004).