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The Journal of Neuroscience, August 16, 2006, 26(33):8523-8530; doi:10.1523/JNEUROSCI.0846-06.2006

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Behavioral/Systems/Cognitive
Transient Functional Suppression and Facilitation of Japanese Ideogram Writing Induced by Repetitive Transcranial Magnetic Stimulation of Posterior Inferior Temporal Cortex

Yoshino Ueki,¹ Tatsuya Mima,¹ Kimihiro Nakamura,² Tatsuhide Oga,¹ Hiroshi Shibasaki,^1,3 Takashi Nagamine,¹ and Hidenao Fukuyama¹

¹Human Brain Research Center, Kyoto University Graduate School of Medicine, Sakyo-ku, Kyoto 606-8507, Japan, ²Section of Speech Physiology, Department of Speech and Cognitive Neuroscience, University of Tokyo, Bunkyo-ku, Tokyo 153-8914, Japan, and ³Department of Neurology, Takeda General Hospital, Fushimi-ku, Kyoto 601-1495, Japan

Correspondence should be addressed to Dr. Tatsuya Mima, Human Brain Research Center, Kyoto University Graduate School of Medicine, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan. Email: mima{at}kuhp.kyoto-u.ac.jp

The Japanese writing system is unique in that it is composed of two different orthographies: kanji (morphograms) and kana (syllabograms). The retrieval of the visual orthographic representations of Japanese kanji is crucial to the process of writing in Japanese. We used low-frequency repetitive transcranial magnetic stimulation (rTMS) to clarify the functional relevance of the left and right posterior inferior temporal cortex (PITC) to this process in native Japanese speakers. The experimental paradigms included the mental recall of kanji, kana-to-kanji transcription, semantic judgment, oral reading, and copying of kana and kanji. The first two tasks require the visualization of the kanji image of the word. We applied 0.9 Hz rTMS (600 total pulses) over individually determined left or right PITC to suppress cortical activity and measured subsequent task performance. In the mental recall of kanji and kana-to-kanji transcription, rTMS over the left PITC prolonged reaction times (RTs), whereas rTMS over the right PITC reduced RTs. In the other tasks, which do not involve the mental visualization of kanji, rTMS over the left or right PITC had no effect on performance. These results suggest that the left PITC is crucial for the retrieval of the visual graphic representation of kanji. Furthermore, the right PITC may work to suppress the dominant left PITC in the neural network for kanji writing, which involves visual word recognition.

Key words: Japanese ideogram writing; kanji; visual word recognition; posterior inferior temporal cortex; PITC; repetitive transcranial magnetic stimulation; rTMS; interhemispheric neural networks

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Received Feb. 24, 2006; revised June 27, 2006; accepted June 29, 2006.

Correspondence should be addressed to Dr. Tatsuya Mima, Human Brain Research Center, Kyoto University Graduate School of Medicine, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan. Email: mima{at}kuhp.kyoto-u.ac.jp

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