A Functional MRI Study on the Japanese Orthographies
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Modulation of the Visual Word Retrieval System in Writing: A Functional MRI Study on the Japanese Orthographies Kimihiro Nakamura1, Manabu Honda2, Shigeru Hirano1, Tatsuhide Oga1, Nobukatsu Sawamoto1, Takashi Hanakawa1, Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/14/1/104/1757408/089892902317205366.pdf by guest on 18 May 2021 Hiroshi Inoue3, Jin Ito3, Tetsu Matsuda1, Hidenao Fukuyama1, and Hiroshi Shibasaki1 Abstract & We used functional magnetic resonance imaging (fMRI) to left sensorimotor areas and right cerebellum. The kanji versus examine whether the act of writing involves different neuro- kana comparison showed increased responses in the left psychological mechanisms between the two script systems of prefrontal and anterior cingulate areas. Especially, the lPITC the Japanese language: kanji (ideogram) and kana (phono- showed a significant task-by-script interaction. Two additional gram). The main experiments employed a 2 Â 2 factorial control tasks, repetition (REP) and semantic judgment (SJ), design that comprised writing-to-dictation and visual mental activated the bilateral perisylvian areas, but enhanced the lPITC recall for kanji and kana. For both scripts, the actual writing response only weakly. These results suggest that writing of the produced a widespread fronto-parietal activation in the left ideographic and phonographic scripts, although using the hemisphere. Especially, writing of kanji activated the left largely same cortical regions, each modulates the visual word- posteroinferior temporal cortex (lPITC), whereas that of retrieval system according to their graphic features. Further- kana also yielded a trend of activation in the same area. more, comparisons with two additional tasks indicate that the Mental recall for both scripts activated similarly the left parieto- activity of the lPITC increases especially in expressive language temporal regions including the lPITC. The writing versus operations regardless of sensory modalities of the input mental recall comparison revealed greater activations in the stimulus. & INTRODUCTION Among a body of literature relating kanji–kana disso- Neurolinguistic studies of Japanese have centered on ciation in brain-damaged patients, kanji-selective agra- the question that neural processing of written language phia in left posterior temporal lesions constitutes a may differ among different script systems, for brain distinct neuropsychological symptom that has been lesions may affect reading or writing abilities differently described by many investigators (Hamasaki et al., 1995; between the ideographic (kanji) and phonographic (ka- Sakurai, Sakai, Sakuta, & Iwata, 1994; Yokota, Ishiai, na) scripts, which is a phenomenon seemingly unique to Furukawa, & Tsukagoshi, 1990; Soma et al., 1989; Kawa- this particular language (e.g., Mayeux & Kandel, 1991). hata, Nagata, & Shishido, 1988; Mochizuki & Ohtomo, This ideogram–phonogram dissociation in Japanese, 1988; Kawamura, Hirayama, Hasegawa, Takahashi, & however, may simply represent a ‘‘phenotypic’’ variant Yamamura, 1987). As suggested by the observation that derived from dysfunction of common neuropsycholog- the agraphic patients complain of ‘‘forgetting’’ kanji, the ical mechanisms that should work universally in the symptom has been interpreted as a disorder of mental human brain for processing of written words. This is recall of visual graphic images required for normal especially the case for certain forms of the dissociation writing of kanji (Iwata, 1984). The critical lesions for that are thought to have equivalent language disorders producing the symptom converge on Brodmann’s area in Western languages (e.g., Soma, Sugishita, Kitamura, 37 in the left posteroinferior temporal cortex (lPITC) Maruyama, & Imanaga, 1989). (Soma et al., 1989). Conversely, kana-selective agraphia, the other form of the dissociative agraphia, may appear in parietal or frontal lesions (Sakurai, Matsumura, Iwat- 1Kyoto University, 2National Institute for Physiological subo, & Momose, 1997; Tanaka, Yamadori, & Murata, Sciences, Okazaki, Japan, 3Rakuwa-kai Otowa Hospital, Kyoto, 1987), but none of the reported cases was associated Japan with lPITC damage. This may support the idea that D 2002 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 14:1, pp. 104–115 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/089892902317205366 by guest on 02 October 2021 writing of kana involves a different neuropsychological the standard brain template. Lateralized activation of the mechanism from that of kanji; people may spell out left posterior inferior temporal gyrus was commonly words in the phonographic script by converting their found in the iWD, iMR, and pMR tasks. However, the acoustic images directly to written forms, rather than by pWD task also showed a trend of activation in this area visualizing their graphic forms, because each kana char- (Z = 3.95, uncorrected). acter, having a simple visual structure, has a one-to-one The iWD task yielded extensive activations in the left correspondence with a syllable. A different, fronto-pari- fronto-parietal areas including the middle and inferior etal neural network has been thought to work for this frontal gyri and pre- and postcentral gyri. Bilateral process (Iwata, 1984). activations were found in the medial frontal gyrus, Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/14/1/104/1757408/089892902317205366.pdf by guest on 18 May 2021 We previously demonstrated, using functional mag- cingulate cortex, superior temporal gyrus, superior pa- netic resonance imaging (fMRI), that activity of the rietal lobule, inferior parietal sulcus, basal ganglia, and lPITC increases in both actual writing and visual cerebellum. The pWD task activated the inferior frontal mental recall of logograms in normal subjects (Naka- gyrus, sensorimotor cortices, superior parietal lobule, mura et al., 2000). This result supported Iwata’s and inferior parietal sulcus in the left hemisphere. (1984) proposal that the region participates in writing Bilateral activations were observed in the superior tem- of kanji as a storehouse of visual graphic memory. poral gyrus, medial frontal gyrus, and cingulate cortex. However, despite the ample lesion studies, there has There were also activations in the left basal ganglia and been no neuroimaging evidence that the area acts thalamus and right cerebellum. In the iMR task, there differently between the ideographic and phonographic were bilateral activations in the middle and inferior scripts during the process of normal writing. To frontal gyrus, superior temporal gyrus, inferior parietal address the issue, the present fMRI study employed sulcus, and superior parietal lobule. In the pMR task, a2Â 2 factorial design in which the effects of interest bilateral activations were observed in the cingulate were task (actual writing vs. mental recall) and script cortices, superior temporal gyrus, and inferior parietal type (kanji vs. kana). Since previous neuroimaging sulci. There was also an activation site in the left inferior studies have shown that the lPITC is active when frontal gyrus. Other activation sites included the right people are engaged in visual imagery of letter forms basal ganglia and cerebellar hemisphere and upper regardless of the writing systems used (Nakamura brainstem. et al., 2000; Goldenberg et al., 1989), it is expected In the individual-based analysis, the iWD and pWD that the mental recall of letter images should activate task commonly activated the left fronto-parietal area, the area similarly for kanji and kana. In actual writing, bilateral fronto-temporal junction, left inferior parietal however, the activity of the lPITC may differ between sulcus, left basal nuclei, and right cerebellum in all the the script types, resulting in a task-by-script interaction subjects. The iWD and pWD tasks yielded activations in in this area. In addition, we tested two different the left dorsolateral prefrontal cortex in eight and five behavioral tasks using the same word stimuli as con- subjects, respectively. In both tasks, activation of the left trols for a baseline activation that may reflect early cingulate cortex and medial frontal gyrus and bilateral auditory–verbal processing of the verbal materials. superior parietal lobules was observed in seven subjects. Both of the mental recall tasks activated the bilateral RESULTS superior temporal areas and left inferior parietal sulcus in all the subjects. The iMR task activated the bilateral Behavioral Data superior parietal lobules in nine subjects, while the pMR Response accuracy for the writing-to-dictation of kanji task yielded activation in the same area in seven sub- ideograms (iWD), writing-to-dictation of kana phono- jects. The iMR and pMR tasks activated the left dorso- grams (pWD), mental recall of kanji ideograms (iMR), lateral prefrontal cortex in seven and six subjects, mental recall of kana phonograms (pMR), and semantic respectively. Activation of the left anterior cingulate judgment (SJ) tasks during scanning was 96.5 ± 3.8%, cortex and medial frontal area was found in eight 98.5 ± 2.7%, 95.5 ± 4.2%, 97.3 ± 4.2%, and 95.8 ± 4.3%, subjects in iMR, while activation of these areas was respectively (mean ± SD). Accuracy of all the subjects observed in six subjects in pMR. exceeded 87% in each of the tasks. They also reported For the lPITC, the number of activated voxels and that they could repeat most of the auditory word stimuli peak Z scores of the individual-based