PET scans showing increased blood flow to active areas of the left hemisphere enable researchers to pinpoint some of the regions involved in different aspects of language processing. Hearing words activates the auditory cortex as well as Wernicke's area, near the junction of the parietal and temporal lobes. Silent reading engages the visual cortex, in the occipital lobe, and the association area for visual memory, which extends into the lower part of the temporal lobe. Speaking activates a region in the motor cortex as well as Broca's area, and thinking about words engages the limbic association area responsible for thought, learning, perception, and emotion.