What do you get if you cross Margaret Thatcher with Marilyn Monroe? A scary prospect, you might think, but, as a recent report in Nature Neuroscience shows, this bizarre-sounding approach provides fascinating insights into how the brain recognizes faces.

Pia Rotshtein and co-workers at University College London morphed images of famous faces into those of different celebrities — for example, Maggie to Marilyn and Tony Blair to Pierce Brosnan. Volunteers were shown images from various points along the morph continuum, and brain activity was measured as they tried to put a name to the face.

Three brain areas were activated during recognition: “the inferior occipital gyri...picked up on small physical changes in the morphed faces. The right fusiform gyrus...forced the face into a known or unknown category. The anterior temporal cortex...is believed to store facts about people we know, and was more active when volunteers were very familiar with the face” (Scotsman, UK, 13 December). Damage to these areas is associated with impaired face recognition: “dementia patients with damage to the anterior temporal cortex have a problem finding the name to go with the face, while people with epilepsy triggered by the right fusiform gyrus sometimes believe that different faces belong to the same person” (Guardian, UK, 13 December).

Rotshtein adds “the brain tries to force us to pin a single identity on a face, even if it looks like a mix of two people we know” (Scotsman). So “a face 60 per cent Marilyn and 40 per cent Margaret Thatcher will be identified as an older Marilyn, while an image 40 per cent Monroe and 60 per cent Thatcher will be seen as the sexier side of Margaret” (Daily Mirror, UK, 13 December).