OBJECTIVETo localize the language cortex associated with Chinese word processing by magnetic source imaging (MSI).

METHODSEight right-handed and one left-handed healthy native Chinese subjects were examined by magnetoencephalography (MEG) and a 1.5T magnetic resonance imaging (MRI) unit. All subjects were given pure tone stimuli 50 times, 150 pairs of Chinese words (meaning related or unrelated) auditory stimuli, and pure tone stimuli subsequently 50 times. Evoked response fields time locked to the pure tone and Chinese words were recorded using a whole-head neuromagnetometer in real-time. The acquired data were averaged by the acquisition computer according to the response to the pure tone, related pairs of words and unrelated pairs of words. The data obtained by MEG were superimposed on MRI, using a GE Signa 1.5T system.

RESULTSMEG, showed there were two obviously higher magnetic waves named M50 and M100, which were localized in the bilateral transverse temporal gyri in all subjects. The responses to the pairs of Chinese words (meaning related or unrelated) were similar in the same hemisphere of the same subjects. There was a higher peak during 300 - 600 ms in the right hemisphere of one left handed subject, but no peak in the left hemisphere, indicating that the language dominant hemisphere was localized in the right hemisphere. Superimposing the MEG data on MRI, the language area was localized in the Wernicke's areas. A 300 - 600 ms response peak was obsarved in each hemisphere (the amplitude of the 300 - 600 ms response peak in each hemisphere was almost the same) in two right-handed subjects, showing that the language area was localized in the 2 hemispheres in the two subjects. There was one peak in each hemisphere (300 - 600 ms response) in 6 subjects, but the amplitude of the wave in the left hemisphere in the 6 subjects was much higher than that in the right hemisphere. By choosing randomly from the later component (300 - 600 ms response) several time points and superimposing them on MRI, all time points were localized in the posterior part of the superior temporal gyri, which is the Wernicke's areas.

CONCLUSIONSComparing with the later component of the bilateral hemispheres, the wave amplitude in the language dominant hemisphere was much higher than that in the non-language dominant hemisphere. The language areas could be identified by judging whether meanings of pairs of Chinese words were related or not.