Reading of Japanese Kanji (morphograms) and Kana (syllabograms): a magnetoencephalographic study.

Magnetoencephalograms were recorded from six healthy Japanese subjects in order to investigate the areas in the cortices which are involved in the recognition of Japanese characters (Kanji and Kana). Forty-four Kanji (morphograms), 44 Kana (syllabograms) and 20 alphabet letters were used as stimuli. They were presented randomly and the subjects were required to read each stimulus and count the number of letters. The magnetic responses were recorded with dual 37-channel SQUID (Superconducting Quantum Interference Device) gradiometers from the temporal, parietal and occipital areas of the brain. The magnetic responses to Kanji and Kana were similar and consequently the locations of equivalent current dipoles (ECDs) to Kanji and those to Kana did not differ at any recording site. In all the subjects, ECDs were found in the posterior inferior temporal (PIT) areas approximately corresponding to Brodmann area 37 in the latency range of 150-300 msec. These activities were found in both hemispheres without consistent laterality. The location of the ECD moved forward from posterior to anterior in the PIT area as the latency increased in all but one subject. Only one subject showed activities in the left angular gyrus. Since activities in PIT areas were also found in alphabet letters, the bilateral PIT areas are considered to play an essential role in reading.