Brain activity when speaking/listening. Coloured positron emission tomography (PET) scans of human brain areas active while speaking and listening. Activity is red/orange. At top left, monitoring imagined speech lights up the auditory cortex. At top right, working out the meaning of heard words activates other areas of the temporal lobe. At lower left, repeating words activates Wernicke's area for language comprehension (right), Broca's area for speech generation (left) and a motor region producing speech. At lower right, monitor- ing speech activates the auditory cortex. Brain activity was detected using radioactive oxygen-15.