Brain activity viewing faces. Coloured positron emission tomography (PET) scans of the areas of the human brain active while processing faces. The left sides of brains are at left, with their right sides at right. Active parts of the cerebral hemi- spheres are red/orange. The upper two scans show the activity associated with viewing faces. The visual area of the occipital cortex is lit up. The other scans, during face recognition, show most activity in the temporal lobe (lower centre on the scans). The scans involved injecting radioactive oxygen-15 into the bloodstream to allow brain areas with high metabolic activity to be seen.