Brain's auditory centre. Coloured positron emission tomography (PET) scan of the brain during a syllable comprehension exercise. In this axial (horizontal) scan the front of the brain is at top. The scan shows the levels of oxygen and water from low (green & blue) to high (red & white). These levels correspond to brain activity. The most active areas (white) are in the auditory cortex of the temporal lobes on either side of the brain. PET scans use radioactively-labelled substances introduced into the blood to view metabolic activity in the brain. See P335/036 for a PET scan taken while listening to background noise.