Deaf people seem to hear signing.

When most people hear sounds or speech, the messages are processed in the auditory cortex, a part of the temporal lobe of the brain. A portion of this auditory cortex is activated in deaf people when they interpret sign language, Japanese scientists assert in the Jan. 14 Nature.

Hiroshi Nishimura's team at Osaka University Medical School in Suita City used positron emission tomography (PET) to measure brain activity in a person who had been deaf since birth. First, the person was shown a still picture of someone signing a word. This elicited little activity in the auditory cortex. Researchers then played a motion video of a person signing many words. A part of the auditory cortex called the secondary region was activated in the deaf person watching the video.

The individual then underwent surgery to receive a cochlear implant, which permitted some hearing. When the researchers played a sound, PET tests revealed that the primary region, but not the secondary region, of the patient's auditory cortex was activated. The patient was also shown a video of a person's hands moving in a meaningless way. This activated the visual cortex, a separate area of the brain, but not the auditory cortex.

These tests suggest that a deaf person's brain changes to make use of the auditory cortex's secondary region for processing sign language. The primary region of the auditory cortex is reserved for hearing sounds, the researchers propose.