Sight, hearing, speaking, thinking. Coloured Positron Emission Tomography (PET) scans of areas of the human brain activated by different tasks. The left-side of the brain is seen. At upper left, sight activates the visual area in the occipital cortex at the back of the brain. At upper right, hearing activates the auditory area in the super- ior temporal cortex of the brain. At lower left, speaking activates the speech centres in the insula and motor cortex. At lower right, thinking about verbs and speaking them generates high activity, including in hearing, speaking, temporal and parietal areas. PET scans detect blood flow.