Brain (2000), 123, 954–967
Participation of the left posterior inferior temporal
cortex in writing and mental recall of kanji
orthography
A functional MRI study
Kimihiro Nakamura,1 Manabu Honda1,3 Tomohisa Okada,2,3 Takashi Hanakawa,1 Keiichiro Toma,1
Hidenao Fukuyama,1 Junji Konishi2 and Hiroshi Shibasaki1
Departments of 1Brain Pathophysiology and 2Nuclear
Medicine, Kyoto University Graduate School of Medicine
and 3Laboratory of Cerebral Integration, National Institute
for Physiological Science, Kyoto, Japan
Correspondence to: Hiroshi Shibasaki, MD, Department of
Brain Pathophysiology, Kyoto University Graduate School
of Medicine, 54 Shogoin, Sakyo, Kyoto 606-8507 Japan
E-mail: [email protected]
Summary
To examine the neuropsychological mechanisms involved
in writing kanji (morphograms), we used functional MRI
(fMRI) in 10 normal volunteers, all right-handed, native
Japanese speakers. The experimental paradigms consisted
of kana-to-kanji transcription, mental recall of kanji
orthography and oral reading and semantic judgement
of kana words. The first two tasks require manual and
mental transcription of visually presented kana words
into kanji, respectively, whereas the last two tasks involve
language processing of the same set of stimulus words
without recall of kanji. The transcription and mental recall
tasks yielded lateralized activation of the left posterior
inferior temporal cortex (PITC). By contrast, neither
oral reading nor semantic judgement produced similar
activation of the area. These results, in good accordance
with lesion data, provide converging evidence that the
left PITC plays an important role in writing kanji through
retrieval of their visual graphic images, and suggest
language-specific cerebral organization of writing. The
set of fMRI experiments also provides new neuroimaging
data on the cortical localization of basic language
functions in people using a non-alphabetical language.
Keywords: kanji; posterior inferior temporal cortex; writing; mental recall; functional MRI
Abbreviations: ANOVA ⫽ analysis of variance; fMRI ⫽ functional magnetic resonance imaging; L–R ⫽ left–right; PITC ⫽
posterior inferior temporal cortex; SPM ⫽ statistical parametric mapping
Introduction
Numerous observations have been reported on brain-damaged
Japanese patients presenting with dissociation of the skills
required to read or write two different orthographic systems:
kana (syllabograms) and kanji (morphograms). These
observations have led to the idea that the processing of kanji
and kana may involve different inter- and intrahemispheric
mechanisms (Iwata, 1984; Benson, 1985; Coltheart, 1987;
Friedman, 1993). For example, Iwata proposed that the left
occipitotemporal areas are especially important for reading
and writing kanji, whereas the more dorsal or occipitoparietal
neural connection plays a role in reading kana (Iwata, 1984).
However, a more comprehensive study by Sugishita and
colleagues demonstrated that patterns of kanji–kana
dissociation in oral reading vary among patients so much that
the neuroanatomical relationship between the phenomenology
© Oxford University Press 2000
and the lesion sites may not be straightforward (Sugishita
et al., 1992).
By contrast, focal damage to the left posterior inferior
temporal cortex (PITC) affects the writing of kanji rather
consistently (Iwata, 1984; Kawamura et al., 1987; Kawahata
et al., 1988; Mochizuki and Ohtomo, 1988; Soma et al.,
1989; Yokota et al., 1990; Sakurai et al., 1994; Hamasaki
et al., 1995). The left PITC lesions in most of the cases were
caused by cerebrovascular accidents, and were accompanied
in the early phase by other signs such as alexia of kanji and
anomia. More recent work, however, suggests that only kanji
agraphia persists in the chronic stage (Kawahata et al., 1988;
Mochizuki and Ohtomo, 1988; Soma et al., 1989; Yokota
et al., 1990). Soma and colleagues proposed that this is a
single, core linguistic deficit due to left PITC damage in
Posterior temporal activation in writing
Japanese patients, and stated that the critical lesion for
producing the symptom is located in Brodmann area 37 on
the inferolateral surface of the left temporal lobe (Soma
et al., 1989). In contrast, no single case with left PITC
damage has been reported to present the opposite pattern of
agraphia, i.e. agraphia preferentially affecting kana.
Descriptions of kana agraphia have been sparse, and the
clinical features and lesion sites seem rather heterogeneous
(Tanaka et al., 1987). Kanji agraphia may also appear after
damage to other brain sites, including the left angular gyrus
and the left frontal cortex, but damage to the former site
usually affects the writing of both kanji and kana (Iwata,
1984), whereas damage to the latter site which causes frontal
kanji agraphia is rare (Sakurai et al., 1997). These lesion
data suggest that only the left PITC is consistently correlated
with the processing of a particular orthography, i.e. the
writing of kanji.
The writing impairment is thought to arise essentially from
an inability to recall visual graphic forms of kanji, as
suggested by analysis of writing errors and by anecdotal
reports that the patients complained of ‘forgetting’ letters
(Kawamura et al., 1987; Kawahata et al., 1988; Mochizuki
et al., 1988; Soma et al., 1989). This unique feature suggests
that the left PITC is involved critically in the retrieval of
visual graphic memory. In general, the left occipitotemporal
cortices are thought to play a role in the generation of visual
mental images, as indicated by studies with brain-damaged
patients (Farah, 1989) and PET studies in normal people
(Roland and Gulyás, 1994). The left PITC in particular is
consistently activated while subjects hear or read words to
generate visual images of their referents (Démonet et al.,
1992; Vandenberghe et al., 1996; Warburton et al., 1996;
Mummery et al., 1998), which suggests that this particular
area is involved in the retrieval of visual representations
from the long-term memory store in association with verbal
symbols. It seems likely that the same brain area also
subserves the recall of visual images of kanji stored in longterm memory. Kanji agraphia as a result of left PITC damage
may be based on dysfunction of a similar neuropsychological
process, i.e. retrieval of the mental representation of visual
objects, since the normal writing of kanji is, in principle,
realized by visualizing the graphic forms to be written (Kaiho
and Nomura, 1983; Iwata, 1984).
In the present study, we tested the following hypotheses
concerning the neuropsychological mechanisms for writing
kanji by the use of functional MRI (fMRI) in normal humans.
First, if the left PITC is critically involved in writing kanji,
which obviously requires complex sequential motor control,
the act of writing kanji will increase neural activity not only
in the sensorimotor and classical perisylvian language cortices
but also in the left PITC. Secondly, if access to the visual
graphic memory store is a mandatory process subserved by
the left PITC for the normal writing of kanji, mere mental
imagery of visual configurations of kanji will also activate
the identical brain area even in the absence of overt motor
execution. Thirdly, if the observed activation of the left PITC
955
actually represents the mental retrieval of kanji orthography
and is not a simple by-product of other prelinguistic or
linguistic processing of stimulus materials, it will be expected
that different verbal tasks in the same stimulus condition will
not yield a similar level of neural activity in the left PITC if
they do not involve the recall of kanji. The last point should
also be examined especially with respect to the use of visual
stimuli, because language materials potentially trigger the
automatic activation of a widespread neural network
irrespective of the behavioural tasks engaged (Price et al.,
1996), and also because the ventral visual systems including
the PITC may respond to both verbal and non-verbal visual
materials (Puce et al., 1996).
A few functional imaging studies in the literature have
examined the neural correlates of writing letters. Using PET,
Petrides and colleagues found bilateral activation of the
posterior temporal areas as well as uni- or bilateral activations
of the sensorimotor and parietal cortices in a writing-todictation task (Petrides et al., 1995). In an fMRI study,
Sugishita and colleagues described extensive activation of
the left intraparietal region during the mental writing of kana
characters, but they did not examine the neural activity of
the temporal areas because of technical limitations (Sugishita
et al., 1996). Seitz and colleagues employed two kinds of
handwriting tasks for their PET study, but they reported
activation of the left PITC in neither of them (Seitz et al.,
1997). Therefore, the possible role of the left PITC in normal
writing does not yet seem to be well elucidated. The present
study examines this issue further through the set of
experiments outlined above, thereby also providing new
neuroimaging data on several aspects of verbal processing
in Japanese, disorders of which have attracted universal
interest because of their language-specific neuropsychological features.
Methods
Subjects
Ten healthy volunteers (six males and four females, age
range 20–25 years) were recruited among students at Kyoto
University. None had a history of neurological or psychiatric
disease. All were native Japanese speakers and strongly righthanded, as confirmed by the Edinburgh inventory (Oldfield,
1971). Informed consent was obtained from each subject
prior to the experiment. The protocol of this study was in
accordance with the guidelines determined by the Committee
of Medical Ethics, Graduate School of Medicine, Kyoto
University.
Word stimuli
A set of 60 words in kana script was presented visually
during all four of the activation paradigms described below
(Fig. 1). The kana word stimuli were prepared by transcribing
60 two-character compound kanji words selected from the
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Fig. 1 Stimulus materials and behavioural paradigms. Sixty
Japanese nouns in kana script were used for all four activation
tasks, i.e. the subjects were engaged in different behavioural tasks
upon presentation of the same visual stimuli according to
prespecified instructions. Although usually written in kanji, the
words without homophones can be identified correctly by
phonological decoding of the kana character strings. In the kanato-kanji transcription task the subject wrote down the first
character of each compound kanji word. In the mental recall task
the subject mentally visualized a graphic form of the kanji and
judged whether it belonged to the L–R type (Fig. 2). In the oral
reading task the subjects simply read aloud the stimulus kana
words; in the semantic judgement task they determined whether
the stimulus words represented concrete objects or abstract
concepts.
fundamental vocabulary for Japanese language teaching
(National Language Research Institute, 1984). None of them
represented homophone words. Half of the words represented
concrete nouns and the other half abstract nouns. Concreteness
and imagery levels of 48 of the 60 words were controlled
using the attributes described by Ogawa and Inamura (Ogawa
and Inamura, 1974), although no normative psycholinguistic
data covering all of the 60 words were available at the time
of the present study. The lexical frequency of the words in
most cases exceeded 500 per 1 000 000 (National Language
Research Institute, 1970). All the words used in the study
are conventionally written in kanji, and kana is used for them
only rarely. The 60 kana words prepared as described above
each consisted of two to six kana characters.
Fig. 2 Mental recall of kanji orthography. (A) Visual
configurations of a kanji character can be classified into two
subtypes in terms of a single feature, i.e. some of them can be
split into two horizontally juxtaposed components (left–right
combination or L–R type) while others cannot (non-L–R type).
(B) Subjects mentally visualized the first character of each
compound kanji word and determined whether its graphic form
belonged to the L–R type.
Task 1: kana-to kanji transcription
Upon presentation of each kana word stimulus, the subjects
were asked to write roughly the first character of the
corresponding compound kanji word on a plastic board with
the right index finger (Fig. 1). The interstimulus interval of
3 s was chosen because normal adults require ~1.8 s to write
out a single kanji word to dictation (Kaiho and Nomura,
1983). The subjects could not see the movements of their
fingers. The responses of each subject were monitored with
a video camera and scored off-line.
Behavioural tasks
Four activation tasks, comprising kana-to-kanji transcription,
mental recall of kanji orthography and the semantic judgement
and oral reading of kana words, were used in the present
study (Fig. 1). Visual identification of kana characters (for
details, see below) was used as a common baseline for the
four tasks. In all the tasks, including the baseline task, the
same event sequence was employed for each trial: after a
period of 100 ms during which the subject fixated a cross
(visual angle 1°), either a kana word (activation tasks, 3 ⫾ 1°)
or a single kana character (baseline, 1°) appeared for 400 ms,
and was followed by a response period for 2500 ms. The
kana words or single kana characters were presented randomly
during each task epoch (see below). The order of the four
behavioural tasks was counterbalanced across the subjects.
Task 2: mental recall of kanji orthography
Cognitive psychological studies on the structural description
of kanji characters have extracted several features to define
their visual configurations, among which the left–right
(L–R) combination of letter-constituents (radicals) is a basic
rule which applies to many kanji characters (Kaiho and
Nomura, 1983; Saito, 1997). Some characters are composed
of two radicals that are juxtaposed horizontally, whereas
others have visual configurations whose constituents are not
arranged according to this rule (Fig. 2A). This basic feature
was exploited in the mental recall task in the present
experiment. In each trial, the subjects were instructed to
mentally transcribe each kana word stimulus to kanji script,
Posterior temporal activation in writing
957
i.e. to imagine the visual configuration of a two-character
kanji word corresponding to the stimulus word (Fig. 2B).
The subjects responded by raising the right index finger when
the first character of each kanji compound word was of the
L–R type and otherwise withheld the response. Half of the
60 trials included the L–R type of character and the other
half did not.
images, for each subject. In each session, starting with the
baseline task, seven task epochs, i.e. four for the baseline
and three for the active tasks, alternated every 30 s (except
that the fourth epoch of the baseline lasted 42 s). Therefore,
each session consisted of the alternating epochs of a single
activation task and the baseline task, and no two activation
tasks were performed within the same session.
Task 3: oral reading of kana words
Data analysis
Subjects were asked to read kana words aloud without
moving the jaw. In addition to a tight constraint on jaw
movement to minimize head motion (see below), they were
especially asked not to open the mouth wide; this allowed
the minimally audible vocalization necessary for the execution
of the task.
After image reconstruction, off-line processing of the
functional images was performed on an ULTRA-2
workstation (Sun Microsystems, Mountain View, Calif., USA)
using SPM96 software (Wellcome Department of Cognitive
Neurology, London, UK). Two initial images were discarded
from the analysis to eliminate non-equilibrium effects of
magnetization. Images were corrected for head motion,
resampled every 2 mm using bilinear interpolation, normalized to the standard brain space defined by the Montreal
Neurological Institute (Friston et al., 1995), and spatially
smoothed with an isotropic Gaussian filter (7 mm full width
at half maximum).
Statistical analysis of the fMRI data was performed at
both the individual and group levels. This was intended
especially to demonstrate the consistency of the results by
applying different statistical approaches at the same time.
For the individual-based analysis, the fMRI time series of
each subject were correlated with the boxcar reference
function, to which a high-pass filter (0.5 cycles/min) and
temporal smoothing were applied to remove low-frequency
noise and to improve the signal-to-noise ratio, respectively.
The resulting correlations were transformed into a Z-score
map (SPM{Z}) (Friston et al., 1994). The significant Z value
was thresholded at Z ⬎ 3.09 (corresponding to P ⬍ 0.001
at each voxel level, uncorrected for multiple comparison).
Activated brain structures were identified using the standard
brain atlas of Talairach and Tournoux (Talairach and
Tournoux, 1988). A region of interest was also set on the
left PITC to further evaluate changes in signal in this area
across the four tasks. The 4.6 ml volume region of interest,
covering most of Brodmann area 37 in the left posteroinferior
temporal cortex, was defined in Talairach coordinates as
x ⫽ –62 to –44 mm, y ⫽ –70 to –52 mm, z ⫽ –16 to 0 mm.
For each subject, the ratio of averaged signal intensities in
the task epochs to those in the baseline was calculated by
sampling a voxel with maximum Z score within the region
of interest for each task. (First scans within each epoch were
excluded to discount the lag in a haemodynamic response.)
The resulting percentage changes in signal were subjected to
one-way analysis of variance (ANOVA) to examine the main
effect of task. One-way ANOVA was used to examine the
main effect of task on the percentage changes in signal. They
were compared among the four tasks using post hoc ANOVA
(Fisher’s PLSD). For the multisubject statistical analysis, the
random effects kit for SPM96 (http://www.fil.ion.ucl.ac.uk)
was used. By fitting the haemodynamic response function,
Task 4: semantic judgement of kana words
The subjects were asked to decide whether the stimulus
nouns in kana denoted concrete objects or abstract concepts,
and to signal by raising the right index finger only in response
to abstract nouns (Fig. 1). The mean probability of appearance
of abstract nouns was 50%.
Common baseline
In each trial, a single kana character was randomly presented
for 400 ms, followed by a response period of 2500 ms.
Single characters were used for stimuli so that the subjects
could readily recognize the on and off times of task epochs
during scanning sessions (see below). The subject signalled
only when the kana character
(/ma/) appeared. The
probability of appearance of the target character was 50%.
fMRI procedure
After a 15 min training session, the subject lay supine in the
MRI scanner. Head motion was minimized by the use of
foam padding. The activation tasks were generated using
SuperLab (Cedrus, Phoenix, Ariz., USA) on a Macintosh
computer. The stimuli were back-projected onto a screen
using a video projection system via a mirror placed in the
head coil. Scanning was conducted with a 1.5 T whole-body
MRI system (Horizon; GE Medical, Milwaukee, Wis., USA)
using a standard head coil optimized for whole-brain echoplanar imaging. For functional imaging, we used a gradientecho echo-planar imaging sequence with the following
parameters: TR (repetition time) 6 s, TE (echo time) 43 ms,
flip angle 90°, field of view 22 ⫻ 22 cm, and pixel matrix
dimensions 64 ⫻ 64. A long TR, as used in recent fMRI
studies, enables coverage of the whole brain (Cornette et al.,
1998; Lobel et al., 1998). Thirty-two contiguous 3.5 mm
thick slices without gaps were obtained in the axial plane
for each subject. For each task, there were two scanning
sessions, each lasting 222 s and yielding 37 functional
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K. Nakamura et al.
Table 1 Maximum Z scores and the number of activated voxels in the left PITC in the four tasks
Subject
1
2
3
4
5
6
7
8
9
10
Transcription
Mental recall
Oral reading
Max.
Z score
No. of
voxels
Max.
Z score
No. of
voxels
Max.
Z score
No. of
voxels
Max.
Z score
No. of
voxels
6.92
5.90
–
5.59
7.29
4.39
6.05
5.29
6.03
5.79
129
205
–
32
253
17
207
73
29
252
4.02
4.69
4.46
4.27
5.55
5.26
5.80
6.26
–
3.70
20
78
14
42
48
90
102
154
–
7
–
5.04
–
–
–
5.87
–
4.69
–
–
–
36
–
–
–
104
–
77
–
–
–
4.44
–
–
–
4.22
5.27
–
–
–
–
28
–
–
–
22
16
–
–
–
images of the individual-level activation parameter were
computed as an adjusted mean image per condition per
session for each subject. The two adjusted mean images
derived from two scanning sessions were collapsed into a
straight mean image per condition per subject. For the
intersubject analysis, a paired t-test was applied to the
condition-specific mean images by the use of the PET
routine of SPM96. The PET statistics thus comprised eight
experimental conditions, i.e. four for the active tasks and
four for their respective baselines. A threshold of Z ⬎ 3.09
was used to determine the presence of significant activation
foci. The extent of clusters was corrected at P ⬍ 0.05 for
multiple comparison. To demonstrate common activation
foci across the task conditions, conjunction analysis of the
transcription and mental recall tasks to their respective
baselines was performed in addition (Price and Friston, 1997).
A conjoint activation map that essentially reflects the sum of
all the activations was constructed from the two independent
SPMs (statistical parametric maps), eliminating voxels where
differences between the two contrasts were significant. This
approach can be applied to combinations of SPMs obtained
by subtractions and enables statistical inference irrespective
of interactions among cognitive components. For comparisons
among the four tasks, uncorrected Z values are also reported
in order to describe the trend of activation. Additionally, the
region of interest defined above was applied to report the
Z scores in this area in the oral reading and semantic
judgement tasks.
Results
Behavioural data
Response accuracy (mean ⫾ standard deviation) in the
transcription, mental recall, semantic judgement and baseline
tasks during scanning was 93.8 ⫾ 4.3, 91.7 ⫾ 3.2, 94.3 ⫾ 3.9
and 98.8 ⫾ 1.4%, respectively. Accuracy of all the subjects
exceeded 85% in each of the tasks. The subjects also reported
that they read aloud all the kana word stimuli successfully
in the oral reading task.
Semantic judgement
fMRI results
Individual analysis
Table 1 summarizes the number of activated voxels and the
peak Z scores in the left PITC for each task (uncorrected for
multiple comparison). Significant activation of the left PITC
was observed in the transcription and mental recall tasks in
nine subjects, whereas the oral reading and semantic
judgement tasks activated the same area only in three subjects.
In the transcription task there were also activations in the
left sensorimotor areas and inferior frontal gyrus in all 10
subjects. The mental recall task activated the left middle and
inferior frontal gyri in all subjects. In the oral reading task,
the bilateral inferior frontal gyri were activated in all subjects
and the left superior temporal gyri in six subjects. The
semantic judgement task activated the left ventrolateral frontal
cortex, including the middle and inferior frontal gyri, in nine
subjects, and the left inferior parietal lobule in eight subjects.
The left superior temporal gyrus was also activated in
six subjects.
For each task, SPM{Z} maps (Z ⬎ 3.09, uncorrected) for
the 10 subjects are superimposed on axial planes of the
standard brain in Fig. 3. The left PITC activation across the
individual results converged at a single anatomical locus
(x ⫽ –50, y ⫽ –66, z ⫽ –12), where activated clusters
overlapped across eight subjects in transcription and six
subjects in mental recall. In the oral reading task the activated
clusters in the left PITC seen in three subjects did not overlap,
whereas in the semantic judgement task overlapping voxels
across two subjects were located more rostrally on the anterior
bank of the left inferior temporal sulcus (x ⫽ –60, y ⫽ –48,
z ⫽ –10). Figure 4 compares the mean % signal change at
peak voxels within the region of interest among the four
tasks. The signal increase in transcription was salient and
equalled that in mental recall, but only weak responses were
observed in oral reading and semantic judgement. One-way
ANOVA revealed a main effect of task [F(3,36) ⫽ 4.22, P ⫽
0.01]. A post hoc test disclosed a significant difference in
signal increase for the following comparisons: transcription
versus oral reading (P ⬍ 0.01); transcription versus semantic
Posterior temporal activation in writing
959
Fig. 3 Superimposed SPM{Z} maps for 10 subjects on the axial plane. The areas illustrated indicate the overlap in two or more subjects.
The activation in the left PITC overlapped at x ⫽ –50, y ⫽ –64, z ⫽ –14 in eight subjects in transcription and in six subjects in mental
recall (arrows). In oral reading there was no overlap of activated clusters in the left PITC, whereas in semantic judgement an activation
site common to two subjects was located more anterodorsally in the left PITC (x ⫽ –50, y ⫽ –48, z ⫽ –10).
judgement (P ⫽ 0.01); mental recall versus oral reading
(P ⫽ 0.03); and mental recall versus semantic judgement
(P⫽ 0.04). By contrast, the difference did not reach statistical
significance in transcription versus mental recall (P ⫽ 0.56)
or oral reading versus semantic judgement (P ⫽ 0.89).
Group analysis
Brain areas activated in the multisubject analysis are listed
in Tables 2, 3, 4 and 5 for transcription, mental recall, oral
reading and semantic judgement tasks, respectively (corrected
at P ⬍ 0.05). Figure 5 illustrates the activation sites projected
onto the standard brain space for each comparison. The
transcription task yielded extensive activations in the left
frontoparietal lobes, including the inferior and middle frontal
gyri and the precentral and postcentral gyri. Bilateral
activations were found in the supplementary motor areas,
cingulate and lingual gyri, basal nuclei, thalami and cerebellar
hemispheres. In the temporal lobe there was a significant
activation focus in the left inferior temporal and fusiform
gyri. In the mental recall task, there were activations in the
middle and inferior frontal gyri and the cingulate gyrus in
the left frontal lobe. Significant activations were also observed
in the inferior temporal and fusiform gyri and the left
supramarginal gyrus and inferior parietal lobule. Other
activated areas included the bilateral cunei, lingual gyri and
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relative to the last two tasks, for which retrieval of graphic
images is not a prerequisite for subsequent cognitive
processing.
Discussion
Fig. 4 Mean % signal change in the left PITC in each task.
Compared with the small increase in signal in oral reading and
semantic judgement, the left PITC is activated more strongly in
transcription and mental recall. Bars indicate standard errors. #P
⬍ 0.05 compared with oral reading; *P ⬍ 0.05 compared with
semantic judgement. TR ⫽ transcription; MR ⫽ mental recall;
OR ⫽ oral reading; SJ ⫽ semantic judgement.
cerebellar hemispheres. Conjunction analysis of the two tasks
to their respective baselines further revealed activations in
the left inferior temporal gyrus and bilateral medial frontal
cortices, inferior parietal areas, medial occipital areas, thalami
and cerebellar hemispheres (corrected at P ⬍ 0.05). The oral
reading task yielded significant bilateral activations in the
inferior frontal gyrus and superior and middle temporal
gyri. There were also bilateral activations in the precentral,
postcentral and lingual gyri and cerebellum. In addition, a
weaker tendency of activation was detected in the left PITC
(Z ⫽ 2.86, P ⫽ 0.002). In the semantic judgement task,
significant activations were observed in the left perisylvian
areas, including the middle and inferior frontal gyri, insular
cortex and superior temporal gyrus. Activated clusters were
also found in the bilateral lingual gyri and cerebellar
hemispheres. There was also a weak trend of activation in
the left PITC (Z ⫽ 2.76, P ⫽ 0.003).
Five additional contrasts were examined to compare the
responses of the whole brain to the four tasks. This was done
by comparing contrasted tasks with each other. For example,
transcription versus its baseline was contrasted with oral
reading versus its baseline. For simplicity, this comparison
is referred to as ‘transcription – oral reading’. The following
comparisons were included: transcription – oral reading;
transcription – semantic judgement; mental recall – oral
reading; mental recall – semantic judgement; and
(transcription ⫹ mental recall) – (oral reading ⫹ semantic
judgement). Results of the first four contrasts are reported in
Table 6 (each thresholded at Z ⬎ 3.09, uncorrected). A trend
of activation was found consistently in the left PITC through
the four comparisons, but there was no other cortical area
that acted similarly. Figure 6 illustrates SPM{Z} for the fifth
contrast, which also revealed activation of the left PITC
We carried out a set of experiments to elucidate the
neuropsychological mechanisms for the writing and mental
recall of kanji, focusing on the role of the left PITC predicted
from lesion data. Despite the technical advances of the
last decade, only a few investigators have used functional
neuroimaging to examine the neural correlates of reading
and writing Japanese (Sakurai et al., 1992, 1993; Sugishita
et al., 1996), including some neurolinguistic investigations
on brain-damaged patients (Morton and Sasanuma, 1984;
Paradis et al., 1985). The activation paradigms in the present
study included kana-to-kanji transcription, mental recall of
kanji orthography, oral reading and semantic judgement,
which involved different kinds of verbal processing of the
same kana word stimuli. Because we designed the
experiments to test particular hypotheses, the motor response
differed inherently among the task conditions. To compensate
for this, we adopted the cognitive conjunction approach for
group analysis of the fMRI data.
Figure 7 illustrates the verbal operations involved in each
task, based on a psycholinguistic model of written word
processing in Japanese (Sasanuma, 1987b). Because kana
script is rarely used to represent the 60 words selected for
the present study, the lexical or whole-word reading strategy
(Marshall and Newcombe, 1973) is unavailable for the
decoding of the unfamiliar kana words (this exceptional
condition is roughly comparable to that in which an English
speaker reads words spelled with phonetic symbols). Thus
the lexical property of the stimuli should be identified through
serial or letter-by-letter phonological conversion of each kana
character, which activates phonological lexicons.
Transcription and mental recall tasks require the digital and
mental retrieval of kanji orthography from the long-term
memory store, respectively, whereas oral reading and
semantic judgement tasks do not involve the visualization of
kanji orthography as an obligatory component. We tested the
last two tasks, which reflect the phonological and semantic
processing of stimulus words, respectively, in order to
compare the activation patterns with those occurring during
the first two tasks. The common baseline task was aimed at
differentiating the activation patterns among the four active
conditions, because all of them share the visual identification
of kana characters as an initial prelexical process for
subsequent higher-order language processing (Fig. 7). It was
used also in an attempt to cancel the influence of early visuoverbal processing of the stimulus words, as several lines of
evidence have indicated that neurons in the ventral visual
stream are involved in the processing of various verbal and
non-verbal visual stimuli (Luders et al., 1991; Puce et al.,
1996; Büchel et al., 1998).
Posterior temporal activation in writing
961
Fig. 5 Brain areas activated in the four tasks (group analysis). The left side of the coronal image corresponds to the left side of the brain.
(A) Transcription. In addition to the extensive activations in the left sensorimotor cortices, a significant activation focus was detected in
the left PITC (arrow). (B) Mental recall. Clusters of significant activations were observed in the left perisylvian cortices, including the
middle and inferior frontal, superior temporal and supramarginal gyri. A distinct activation was also found in the left PITC (arrow). (C)
Oral reading. Although bilateral activations were found in the bilateral perisylvian and sensorimotor areas, there was no significant
activation in the PITC in either hemisphere. (D) Semantic judgement. Significant activations were located in the left perisylvian areas,
including the middle and inferior frontal gyri, insula and anterior superior temporal gyrus. There was no significant activation in the left
PITC.
The role of the left PITC in kanji retrieval
The most important finding from the series of analyses in
the present study is that the left PITC is active not only in
actual writing but also in the mental recall of kanji. By
contrast, neural activity in this area did not significantly
change from the baseline during oral reading or semantic
judgement of the same word stimuli. Thus, the observed
activation of the left PITC should be attributed neither to the
motor execution of writing per se nor to non-specific neural
response to the visual stimuli. Rather, as a conjoint activation
focus of the first two tasks, it was specifically correlated with
the retrieval of kanji graphic images, which is commonly
implicated in these tasks, whereas no comparable signal
increase was found in the same area in the last two tasks,
which do not require such cognitive operations. The activation
site overlaps precisely the lateral surface of the left posterior
temporal lobe, corresponding mostly to Brodmann area 37,
to which Soma and colleagues pointed as the lesion site
critical for producing the pure agraphia of kanji (Soma et al.,
1989). The activation of the left PITC during the mental
recall of kanji is in good accordance with the classical
interpretation of the syndrome—that it might arise from
impaired recall of the visual graphic memory (Kawahata
et al., 1988; Mochizuki and Ohtomo, 1988; Soma et al.,
1989; Hamasaki et al., 1995).
The writing disorder uniquely found among Japanese
patients with a left PITC lesion may differ from the
symptomatology found in subjects using Western languages,
in which damage to the same brain site produces pure alexia,
anomia (Greenblatt, 1976; Henderson et al., 1985) and rarely
lexical agraphia (Croisile et al., 1989). Traditionally, the
kanji agraphia after left PITC lesion has been thought to
962
K. Nakamura et al.
Table 2 Brain regions activated by the transcription task
Brain area
No. of
voxels
Cluster level
P value
Talairach coordinates (mm)
x
Left inferior frontal gyrus
141
Left frontoparietal area
2555
Medial frontal gyrus
Cingulate gyrus
Precentral gyrus
Inferior parietal area
Left inferior temporal gyrus
124
Bilateral basal ganglia and thalami
476
Bilateral medial occipital areas and 2654
cerebellum
z
–47
⫹1
⫹24
5.05
–1
–3
–20
–36
–43
⫹10
⫹20
–7
⫹4
–13
–40
–63
⫹4
–50
⫹57
⫹33
⫹50
⫹50
–11
⫹3
–26
5.21
4.39
4.96
5.19
4.47
5.10
5.80
0.016
0.000
0.026
0.000
0.000
y
Max.
Z score
Table 3 Brain regions activated by the mental recall task
Brain area
No. of
voxels
Left inferior frontal gyrus
605
Left cingulate gyrus
101
Left inferior temporal gyrus
94
Left inferior parietal lobule
192
Bilateral medial occipital areas and 1696
cerebellum
Cluster level
P value
0.000
0.051
0.065
0.005
0.000
Talairach coordinates (mm)
x
y
z
–38
–3
–45
–36
⫹10
⫹24
⫹10
–56
–38
–77
⫹13
⫹44
–10
⫹40
–17
Max.
Z score
4.87
3.86
4.20
4.27
5.26
Table 4 Brain regions activated by the oral reading task
Brain area
No. of
voxels
Cluster level
P value
Talairach coordinates (mm)
x
Left frontotemporal junction
Left frontotemporal area
Left frontoparietal area
Left medial occipital area and
cerebellum
Right medial occipital area and
cerebellum
y
Max.
Z score
z
337
1601
363
486
0.000
0.000
0.000
0.000
–54
⫹64
–48
–20
⫹8
–20
–9
–82
⫹34
⫹12
⫹31
–14
4.50
5.39
4.91
5.52
151
0.009
⫹16
–64
–22
4.60
Table 5 Brain regions activated by the semantic judgement task
Brain area
No. of
voxels
Cluster level
P value
Talairach coordinates (mm)
x
Left middle frontal gyrus
Left frontotemporal junction
Left medial occipital area and
cerebellum
Right medial occipital area and
cerebellum
y
z
Max.
Z score
381
162
365
0.000
0.007
0.000
–38
–45
–13
⫹10
⫹28
–81
⫹34
⫹3
–24
5.21
4.74
4.36
155
0.008
⫹8
–74
–19
4.16
represent a Japanese equivalent of lexical agraphia because
of their similar neurolinguistic features and the proximity of
the lesion sites (Soma et al., 1989; Yokota et al., 1990;
Sakurai et al., 1997). In most reported cases of lexical
agraphia, however, the lesions responsible were located more
dorsally, at the left occipitoparietal junction (Roeltgen, 1993).
Interestingly, the left posterior temporal activation in Englishspeaking people that Petrides and colleagues found in the
‘writing words to dictation’ task (Petrides et al., 1995) is
also localized more dorsally (x ⫽ –50 mm, y ⫽ –66 mm,
z ⫽ 5 mm in Talairach coordinates) than the PITC activation
found in the present study. Taking these results together, it
Posterior temporal activation in writing
963
Table 6 Brain areas activated in direct comparisons among the tasks
Brain area
Frontal
R middle frontal gyrus
L inferior frontal gyrus
R medial frontal cortex
L medial frontal cortex
L frontoparietal area
L cingulate cortex
Temporal
R superior temporal gyrus
L inferior temporal gyrus
Parietal
R superior parietal lobule
L inferior parietal sulcus
R precuneus
L precuneus
Subcortical
R basal ganglia/thalamus
L basal ganglia/thalamus
R cerebellum
L cerebellum
Transcription
minus
oral reading
Transcription
minus
semantic judgement
Mental recall
minus
oral reading
Coordinates
(x, y, z)
Z
score
Coordinates
(x, y, z)
Z
score
Coordinates
(x, y, z)
⫹24, –3, ⫹49
4.01
⫹22, –3, ⫹49
4.08
⫹6, ⫹48, ⫹46
3.89
–31, –38, ⫹54
6.08
Mental recall
minus
semantic judgement
Coordinates
(x, y, z)
Z
score
⫹32, ⫹12, ⫹39 3.93
–45, ⫹28, ⫹19 4.48
–20, ⫹4, ⫹49
3.78
4.51
6.45
5.16
–13, –5, ⫹40
4.30
–13, ⫹32, ⫹8
3.31
4.81
⫹59, –25, ⫹13 3.70
–41, –58, –10
3.48
–48, –60, –10
4.64
–50, –62, –10
3.40
⫹25, ⫹44, ⫹56 3.87
⫹25, –44, ⫹54 4.00
–36, –38, ⫹36
4.09
⫹27, –58, ⫹49 3.45
–29, –42, ⫹35 3.53
–43, –58, –12
–4, –19, ⫹50
–29, –13, ⫹57
–3, ⫹3, ⫹33
⫹20, –63, ⫹46 3.94
–8, ⫹1, ⫹9
⫹25, –57, –26
4.93
6.55
Z
score
–8, –79, ⫹38
–15, –25, ⫹11
⫹13, –62, –21
⫹8, ⫹20, ⫹1
3.61
–43, –56, –21
3.72
3.68
4.66
7.10
Each of the contrasts was computed by comparing a pair of tasks relative to their respective baselines. L ⫽ left; R ⫽ right.
is possible, despite the apparent resemblance in
symptomatology, that writing alphabetical letters and kanji
are controlled by different subregions within the left
temporoparietal cortex.
The finding that the left PITC is indeed activated by the
retrieval of kanji, however, does not preclude the possibility
that the area could also be active when subjects form visual
images of kana characters. Lesion studies and functional
imaging data in normal humans indicate that the left
occipitotemporal regions serve for the generation of various
kinds of mental images, including non-verbal motor imagery
(Farah, 1989; Roland and Gulyás, 1994). In particular,
Goldenberg and colleagues reported activation of the left
PITC in an alphabet-scrutinizing task in which subjects were
engaged in visual imagery of alphabetical letters (Goldenberg
et al., 1989). Thus, the left PITC is likely to be involved in
the mental recall of other script systems as a key cortical
area linking encoded verbal input to visual graphemic images.
In the act of writing, however, the area plays an especially
important role for kanji, which should be more dependent
than phonographic scripts on the effective visualization of
graphic forms.
Furthermore, the present results suggest that retrieval of
the kanji graphic images occurs mainly in the left hemisphere.
Kawamura and colleagues reported that the ability to write
kanji was lateralized to the left hemisphere in a patient with
left unilateral kanji agraphia due to destruction of the posterior
corpus callosum (Kawamura et al., 1989), while another
study on callosal disconnection suggested that this ability
could be shared by the right hemisphere (Yamadori et al.,
1983). In the present study, none of the subjects showed
unilateral right-sided activation of the PITC. Although a
possible advantage of the right hemisphere has long been
speculated for the visual processing of kanji (Benson, 1985;
Coltheart, 1987), the overall tendency, as seen from our
individual fMRI data, is that the left hemisphere functions
predominantly in the active retrieval of graphic images of
kanji in right-handed people.
Frontal activations in decoding kana script
The left ventrolateral frontal cortex or Broca’s area was
commonly activated in all the four contrasts. It probably
reflects phonological decoding of the kana character strings
that occurs prelexically, as all the tasks involve this component
at the initial stage of word processing (Fig. 7). The importance
of the area in reading kana has been suggested by lesion
studies showing that performance in the reading of kana
tends to be more severely affected in patients with Broca’s
aphasia (Paradis et al., 1985), which may be interpreted as
the breakdown of a ‘phonological processor’ essential for
translating kana characters into phonology (Sasanuma and
Fujimura, 1971). For the transcription and oral reading tasks,
however, the activation observed could also be associated
with the motor execution of reading and writing, respectively.
Mental recall and semantic judgement strongly activated
964
K. Nakamura et al.
Fig. 6 Unilateral activation of the left PITC (arrow). The figure
illustrates SPM{Z}, where transcription ⫹ mental recall is
compared with oral reading ⫹ semantic judgement. (The task
conditions are contrasted with their respective baselines.) Note
that the activation focus in the left PITC that was commonly
found in the first two tasks survived direct comparison with the
last two tasks. Other activations were in the right medial frontal
cortex, left frontoparietal junction, bilateral superior parietal areas
and right cerebellum. The figure is corrected at P ⬍ 0.05 for the
purpose of display.
the left dorsolateral prefrontal cortex, and inferior frontal
activation in transcription also extended to this area. Previous
functional imaging data have consistently reported activation
of this area during tasks which involve the semantic
processing of words through access to visual or verbal longterm memory (Démonet et al., 1992; Vandenberghe et al.,
1996; Warburton et al., 1996; Binder et al., 1997). That only
oral reading yielded no similar activation of the area may be
accounted for by the assumption that this task involves
principally simple letter-to-sound conversion rather than
activation of further lexical–semantic processing.
Oral reading and semantic processing of kana
words
Oral reading of kana words activated the bilateral perisylvian
frontotemporal cortices. Sakurai and colleagues used similar
activation paradigms in their PET study (Sakurai et al.,
Fig. 7 Psycholinguistic processing involved in the activation
paradigms used in the study. When a word that is only rarely
written in kana is presented visually in kana, it is identified as a
lexical item through letter-by-letter phonological decoding. The
word thus identified is transcribed into kanji script by explicit or
implicit retrieval of a visual graphic image of the kanji
(transcription, TR). Direct conversion from the phonological
lexicon to a kanji motor grapheme, which is rather unlikely, may
be operating in rare cases. Mental recall of kanji orthography
requires retrieval of visual images of kanji (mental recall, MR).
By contrast, oral reading of the kana word is achieved through
either the direct letter-by-letter phonological pathway or the
indirect lexical–semantic pathway (oral reading, OR). The same
kana word is subject to the subsequent semantic processing
(semantic judgement, SJ) which follows the phonological
decoding of kana characters. Note that retrieval of the kanji
configuration is neither required nor obligatory in the last two
tasks. All four types of language processing have the visual
identification of each kana character as the common initial
component (baseline, BL).
1993). Although the distribution of the activated areas that
they reported is mostly consistent with ours, they also
described activation of the bilateral (left-side predominant)
activation of the PITC, which was not observed in the present
study but could be attributed to a difference in the baseline
condition. Because a resting state with visual fixation was
used in their study, the PITC activation should be interpreted
as reflecting the visual recognition of stimulus letters; this
Posterior temporal activation in writing
was largely cancelled out in the present study. In another
PET study using the same baseline, they also reported
activation of the PITC during oral reading of kanji words
(Sakurai et al., 1992). As the ventral visual areas are
specialized for the processing of visual objects in humans
(Ungerleider and Haxby, 1994) and are sensitive to various
visual stimuli, as shown by past neuroimaging studies (Price
et al., 1996; Puce et al., 1996), it should be emphasized that
these observations by Sakurai and colleagues (Sakurai et al.,
1992, 1993) are reasonable per se, but are different in nature
from the left PITC activation seen in the present study.
In the semantic judgement task, activations were observed
in the left dorsolateral prefrontal cortex and the left inferior
frontal and anterior superior temporal gyri. While similar
tasks that require semantic-level processing of words have
never been applied to Japanese subjects in functional imaging
studies, our finding largely replicates the results of past studies
with English-speaking people which described activation of
the left lateral frontal and superior temporal cortices (Wise
et al., 1991; Démonet et al., 1992; Howard et al., 1992;
Pugh et al., 1996; Binder et al., 1997). The left inferior
prefrontal or Broca’s area is reported to play an important
role in the reading comprehension of kana words, because
kana script depends more on the phonological decoding
process, whereas the reading comprehension of kanji may
involve direct access to the semantic system (Sasanuma and
Fujimura, 1971; Sasanuma, 1987a; Morton and Sasanuma,
1984).
Some of the present subjects reported that they occasionally
imagined kanji characters corresponding to a stimulus kana
word to determine the meaning of the word in the semantic
judgement task. However, this did not yield a measurable
signal increase in the left PITC, probably because the mental
visualization of kanji is a possible, but not obligatory, process
constantly used, although it might occur in some cases. It is
also possible that subjects visualize referents of the stimulus
words to determine their semantic property, but neither did
this yield significant group-level activation in the temporoparieto-occipital networks involved in visual imagery (Roland
and Gulyás, 1994). This may partly be because half of the
stimulus words were abstract nouns with a very low imagery
level which could evoke no distinct visual representations. It
is more likely, however, that the execution of the task, i.e.
selecting abstract nouns from the list of words, was processed
by higher-order verbal semantic knowledge and did not
necessarily require such visualization of the word referents.
Other activations
The transcription task activated broad areas of the left
frontoparietal cortices. Bilateral activation of the
supplementary motor area was also observed. These areas
are commonly activated by tasks which involve complex
serial movement of the fingers (Roland et al., 1980; Shibasaki
et al., 1993). Activation of the medial occipital areas was
also observed in all the comparisons. Such activation is
965
primarily attributed to the difference in visual stimulus
properties between the active tasks and baseline. This may
imply that the latter might well not control for the very early
stage of visual processing. However, we believe that this is
not a serious drawback of the experimental design as the
response of the early visual area is outside the interest of the
current experiments.
Conclusion
The present study demonstrated that the left PITC was
activated in normal people equally for the writing and
for the mental recall of kanji orthography. By contrast,
phonological and semantic processing of the same words
activated the left perisylvian frontotemporal areas, but did
not yield similar activation in the PITC. Overall, the results
support the hypothesized neural pathway for writing kanji
(Iwata, 1984), whereby the left PITC plays a central role in
the recall of the ‘visual engrams of letters’. In the act of
writing, even in writing kanji, one may not make a conscious
effort to recall the visual images of letters or words to be
written, because the sequential visuomotor skill appears to
proceed rather automatically in normally educated adults. In
this series of experiments we found that the skill is supported
by the neural subsystem that is specialized for the retrieval
of visual graphic forms. Coupled with lesion data, our results
provide converging evidence that the left PITC essentially
subserves this retrieval process and allow further insights
into the neuropsychological mechanisms for writing.
Acknowledgements
This research was supported by Grants-in-Aid for Scientific
Research (A) 09308031, for Scientific Research on Priority
Areas 08279106 and for International Scientific Research
10044269 from the Japan Ministry of Education, Science,
Sports, and Culture, Research for the Future Program JSPSRFTF97L00201 from the Japan Society for the Promotion
of Science, and General Research Grants for Aging and
Health ‘Physiological parameters for evaluation of aging of
brain’ and ‘Analysis of aged brain function with neuroimaging
techniques’ from the Japan Ministry of Health of Health
and Welfare.
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Received May 25, 1999. Revised October 25, 1999.
Accepted November 16, 1999