Image-processing brain activity. Coloured positron emission tomography (PET) scans of the human brain areas active while processing images of objects. The left sides of the brains are seen, with active parts red/orange. At top, the visual area of the occipital cortex is activated as objects are seen. At centre, areas within the temporal lobe light up as objects are recognised. At bottom, speech and motor areas within the frontal cortex (centre left of scan) are activated as objects are named. The scans involved injecting radioactive oxygen-15 into the bloodstream so that the areas of the brain with high metabolic activity can be seen.