Distinct role of spatial frequency in dissociative reading of ideograms and phonograms: An fMRI study

• Published in: NeuroImage (Orlando, Fla.) Vol. 63; no. 2; pp. 979 - 988
• Main Authors: Horie, Shizuka, Yamasaki, Takao, Okamoto, Tsuyoshi, Kan, Shigeyuki, Ogata, Katsuya, Miyauchi, Satoru, Tobimatsu, Shozo
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-11-2012; Elsevier Limited
• Subjects: Activated; Activation; Adult; Brain; Brain - physiology; Brain Mapping; Circuits; Experiments; Female; Fourier analysis; Fourier transforms; Functional MRI (fMRI); High and low spatial frequencies; Humans; Image Interpretation, Computer-Assisted; Information technology; Japanese Kana (phonogram); Japanese Kanji (ideogram); Links; Magnetic Resonance Imaging; Male; Parallel visual pathways; Pattern Recognition, Visual - physiology; Phonetics; Photic Stimulation; Pictographs; Reading; Reading processing; Semantics; Stimuli; Stroke; Studies; Writing; Young Adult; Parallel visual pathways; Functional MRI (fMRI); Japanese Kana (phonogram); High and low spatial frequencies; Japanese Kanji (ideogram); Reading processing
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2012.03.046

It has been proposed that distinct neural circuits are activated by reading Japanese ideograms (Kanji) and phonograms (Kana). By measuring high-density event-related potentials, we recently reported that spatial frequency (SF) information is responsible for the dissociation between Kanji and Kana reading. In particular, we found close links between Kana and low SF (LSF) information and between Kanji and high SF (HSF) information. However, it remains unclear which brain regions contribute to this dissociation. To determine this, we performed functional magnetic resonance imaging while presenting unfiltered or spatially filtered Kanji and Kana word stimuli to healthy native Japanese subjects. Fourier analysis revealed that Kanji and Kana stimuli were characterized by HSF and LSF information, respectively. When presented with either type of unfiltered stimulus (Kanji or Kana), the bilateral inferior temporal (IT, BA 37) regions were activated compared to the resting condition. Kana but not Kanji reading also activated the bilateral inferior parietal lobules (IPL, BA 40). When we compared Kanji and Kana reading directly, the left IT region was significantly activated by Kanji reading, while significant activation of the left IPL was observed during Kana reading. In response to filtered HSF stimuli, the Kanji reading minus Kana reading comparison revealed significant activation of the left IT region but not the left IPL. Conversely, significant activation of the left IPL but not the left IT region occurred in the Kana reading minus Kanji reading comparison for filtered LSF stimuli. These results suggest that Kanji and Kana engage a relatively overlapping network, within which the left IT is more involved in Kanji processing, while the left IPL contributes more to Kana processing. The preferential engagements of these brain regions could reflect the close links between Kana and LSF information, and between Kanji and HSF information. Therefore, this study provides further evidence that SF contributes to the dissociation between Kanji and Kana reading.
► Role of spatial frequency (SF) in Kanji–Kana reading was assessed with fMRI. ► Close links between high SF and Kanji and between low SF and Kana were found. ► Kanji and Kana are processed in the left inferotemporal and inferior parietal areas.