Reading aloud and silently. Coloured Positron Emission Tomography (PET) scan showing active areas of the human brain involved in reading. The left-side of the brain is seen. Active areas are colour-coded green and yellow. At top, the subject is reading aloud. Active regions of the brain are: visual cortex for sight; motor region for speech production; auditory region as the subject hears the sound of their own voice. At bottom, the subject is reading silently, and only the visual cortex is active during the reading process. PET shows cerebral blood flow as active areas; this is superimposed onto a cartoon image of the brain.