Sight, hearing, braille, thinking. Coloured positron emission tomography (PET) scans of areas of the human brain activated by different tasks. The fronts of the brains are at left. At upper left, sight activates the visual area in the occipital cortex. At upper right, hearing activates the auditory area in the temporal cortex. At lower left, touching braille script activates the tactile parietal area and an area of cognition (lower right of the brain). At lower right, thoughts in the frontal cortex are used to generate words. These scans detected areas of high metabolic activity using the oxygen-15 isotope.