Brain hearing sound. Coloured positron emission tomography (PET) scan of the area of the human brain active while hearing words or sounds. The left side of the brain is seen, with the front at left. Active parts of the cerebral hemisphere are yellow/red. Hearing has activated the auditory area in the superior temporal lobe, part of the brain's cerebrum. The cerebrum also carries out conscious thought processes. The scan involved injecting the radioactive isotope oxygen-15 into the bloodstream to allow areas of the brain with high metabolic activity to be seen.