Neuroscience Research 39 (2001) 1 – 10
www.elsevier.com/locate/neures

Review

Sentence processing in the cerebral cortex
Kuniyoshi L. Sakai a,b,*, Ryuichiro Hashimoto a, Fumitaka Homae aaDepartment of Cogniti6e and Beha6ioral Science, Graduate School of Arts and Sciences, The Uni6ersity of Tokyo, Komaba, 3 -8 -1 Komaba,
Meguro-ku, Tokyo, 153 -8902, Japanb
CREST, Japan Science and Technology Corporation, Kawaguchi-shi, 332 -0012, Japan
Received 15 May 2000; accepted 8 October 2000

Abstract
Human language is a unique faculty of the mind. It has been the ultimate mystery throughout the history of neuroscience.
Despite many aphasia and functional imaging studies, the exact correlation between cortical language areas and subcomponentsof the linguistic system has not been established. One notable drawback is that most functional imaging studies have tested
language tasks at the word level, such as lexical decision and word generation tasks, thereby neglecting the syntactic aspects of
the language faculty. As proposed by Chomsky, the critical knowledge of language involves universal grammar (UG), whichgoverns the syntactic structure of sentences. In this article, we will review recent advances made by functional neurolmaging
studies of language, focusing especially on sentence processing in the cerebral cortex. We also present the recent results of ourfunctional magnetic resonance imaging (fMRI) study intended to identify cortical areas specifically involved in syntactic
processing. A study of sentence processing that employs a newly developed technique, optical topography (OT), is also presented.
Based on these findings, we propose a modular specialization of Broca’s area, Wernicke’s area, and the angular gyrus/supramarginal gyrus. The current direction of research in neuroscience is beginning to establish the existence of distinct modules responsible
for our knowledge of language. © 2001 Elsevier Science Ireland Ltd and the Japan Neuroscience Society. All rights reserved.
Keywords: Language; Speech recognition; Syntax; Semantics; Phonology; Universal grammar (UG); Functional magnetic resonance imaging(fMRI); Optical topography (OT)

1. Introduction
Linguistics has addressed the following key
questions:
1. What constitutes the knowledge of language?
2. How is the knowledge of language acquired?
Evidently, we know about language and can intuitively judge the grammaticality of a sentence as far as
our native language is concerned. But such knowledge
about grammatical rules is mostly implicit, and wecannot fully explain why it is grammatical. An adequate explanation of linguistic knowledge would require a detailed analysis of various sentences inaccordance with a theoretical framework for linguistic
structures. On the other hand, a human child can* Corresponding author. Tel./fax: +81-3-54546261.
E-mail address: sakai@mind.c.u-tokyo.ac.jp (K.L. Sakai).

acquire any natural language within a few years, without the aid of analytical thinking and without explicit
instruction of ‘grammars’ usually taught at school.
Therefore, the origin of grammatical rules should be
ascribed to an innate system located in the humanbrain. Since language is a subsystem of the mind andthe mind itself has biological constraints of the brain,
language inherently reflects some aspects of biologicalproperties. Linguistics can be regarded as an effort todiscover the fundamental laws and general principles
that explain the properties and constraints of language
systems. Noam Chomsky has proposed a generalframework for these inquiries as universal grammar(UG), a concept that revolutionized linguistics andcognitive science (Chomsky, 1957; Smith, 1999; Chomsky, 2000).
It is important to ask how language is related to or
separated from other aspects of the mind. Probably

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K.L. Sakai et al. / Neuroscience Research 39 (2001) 1–10

inspired by Chomsky’s modular approach to the studyof mind (Chomsky, 1980), Fodor (1983) postulated ‘themodularity of mind’, which attributed language to an
input system as one of modules like sensory systems.
However, Chomsky claimed that it is too narrow toregard the ‘language module’ solely as an input system,and that it is rather a ‘central system’ (Chomsky, 1986).
Our position is that the language system does indeed
represent a distinct module, which is segregated fromother systems of the mind, i.e. the modules of perception, memory, and consciousness (Fig. 1). Nevertheless,language closely interacts with these cognitive facultiesof the mind. First, language is encoded by a series ofphonemes (segmental units), and its phonological form
can be perceived either through the auditory perceptionof speech sounds or through the visual perception ofletters and signs. Phonemes are further recognized asmeaningful units or semantic representation of words,
in reference to stored information in long-term memory. As to the modularity of language and memory,there is experimental evidence that syntactic processing
is separable from the working memory system underlying other general functions (Caplan and Waters, 1999).
Further, normal speech comprehension and speech production is only possible in a conscious state. As Dennett (1978) noted, ‘If one supposes…that one’s thinking
is one’s ‘stream of consciousness’,… then we must grantthat thinking is an activity restricted to language-users.’
On the other hand, syntactic operations themselves,
which govern the hierarchical organization of words
and phrases in sentences, are mostly unconscious. These
multiple processes of linguistic information suggest thatthe language system itself has internal modularity(Chomsky, 1984), and that it is further divided into
distinct modules or subsystems, such as phonology,
semantics, and syntax, which interact systematicallywith each other (Fig. 2).
The hypothesis of functional modules states that
individual modules constitute a system as a whole. If
modules of phonology, semantics, and syntax conceivably exist in the language system, information flow
among these modules, as well as the roles of theirFig. 2. Modules of language and their interactions.

Fig. 3. Cortical language areas and their interactions.

interactions should be clarified. A further criticalquestion is whether these modules correspond to distinct areas of the brain. The identification of specialized
cortical areas responsible for these distinct aspects oflinguistic competence is the first step towards understanding how language is instantiated in the brain.
Lesion studies of aphasia, alexia, and agraphia havesuggested three candidate areas for language function:
Wernicke’s area in the superior temporal cortex, AG/
SMG (the angular gyrus (Brodmann’s area (BA) 39)
and the supramarginal gyrus (BA 40) in the parietotemporal cortex, and Broca’s area (the pars opercularis(BA 44) and the pars triangularis (BA 45) in theinferior frontal cortex (Fig. 3). In this paper, we consider Wernicke’s area as containing the planum temporale (BA 42/22), the superior temporal gyrus (BA 22),and the superior part of the middle temporal gyrus (BA21). However, it should be noted that this conventionalterm is often too broad to specify particular areas.
Despite the long history of neurolinguistic studies(Obler and Gjerlow, 1999), the individual roles of theseareas continue to be debated, and the exact correlation
between cortical language areas and subcomponents of
the linguistic system has not yet been established. Recently developed functional imaging techniques addressthese critical issues. Such imaging techniques should be
combined with detailed anatomical studies in order tocontribute to an understanding of both structural andfunctional bases of language information processing.

2. The module of syntactic processing

Fig. 1. A model of reciprocal intertactions between cognitive components of mind and language

One key question that addresses the modular organization of language in the cerebral cortex is the undetermined role of Broca’s area in syntactic processing, anK.L. Sakai et al. / Neuroscience Research 39 (2001) 1–10

3

Fig. 6
Fig. 4. Cortical activation in grammar (GR) and spelling (SP) conditions. (A) GR vs CO; (B) SP vs CO. fMRI images in t-maps weresuperimposed on structural images showing z =4, 12, 20, and 28 horizontal slices for a single representative subject. The color bars at lightindicate the t-values of the comparison. The left side (L) of the brain is shown at the left. Activation during the GR condition was generally
greater in the language areas than activation during the SP condition; this difference was particularly prominent in Broca’s area (B), comparedwith Wernicke’s area (W) and AG/SMG (Embick et al., 2000).
Fig. 6. Superior temporal cortex activation during speech recognition. (A) Story task vs control; (B) Repeat task vs control. OT images in r-maps
for signal changes averaged among all subjects were superimposed on lateral images of a brain. The color bars at night indicate the correlation
coefficient (r) of Coxy time points with a boxcar waveform (each period, 36 s; delay, 6 s). Note the prominent activation in the mid-lateral partof the bilateral temporal cortex.

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K.L. Sakai et al. / Neuroscience Research 39 (2001) 1–10

issue which has been debated from a number of different perspectives. The notion that Broca’s area is a locus
for syntactic processing stems initially from the aphasia
literature. After Broca’s initial insight, Broca’s area was
first regarded as a speech production area, because
patients diagnosed with Broca’s aphasia were relatively
or grossly inarticulate but were able to understandspoken language. The agrammatism of Broca’s aphasics
suggested that Broca’s area is the locus of syntactic
processing or the locus of the grammatical system(Geschwind, 1970; Goodglass, 1976). More recent studies, however, have argued that there is dissociation
between Broca’s aphasics’ problems with syntactic processing/comprehension and lesions in Broca’s area
(Caplan et al., 1996; Dronkers, 1996), although dissenting views on this matter continue to be voiced(Grodzinsky, 2000).
Event-related brain potential (ERP) studies haveidentified a component, the P600, which correlates witha subject’s recognition of syntactic ill-formedness (Osterhout and Holcomb, 1992; Gunter et al., 1997). However, the language specificity of this component has
been challenged (Patel et al., 1998), and the specificcortical generator of the component has not been localized. A second component, the left anterior negativity(LAN), has also been associated with error detection ingrammatical processing (Friederici et al., 1993; Münte
et al., 1993). Its source is once again unclear, but its
detection by left-anterior electrodes is suggestive of theinvolvement of Broca’s area. In the imaging literature,
activation in Broca’s area has been found during theperformance of some linguistic tasks, while other studies have argued for the involvement of Broca’s area indecidedly nonsyntactic processing, such as in thephonological processing of words or letters (Poeppel,
1996; Fiez and Petersen, 1998). Two prior imaging
studies (Stromswold et al., 1996; Just et al., 1996) haveattributed activation in Broca’s area during syntactic
tasks to an increase in general complexity, rather thanto any specific role played by this area as to syntax. In
these studies, increased sentential complexity correlatedwith an increase in activity in Broca’s area. Activity in
Broca’s area in these experiments might stem from thefact that Broca’s area is specifically involved in syntactic processing, but it may simply reflect a general increase in demands on the entire linguistic system. In
addition, verbal short-term memory may be primarily
involved, rather than syntactic processing per se. The
task used in one study was to judge the semantic
plausibility of a visually presented sentence, and sentences with center-embedded and right-branching relative clauses were compared (Stromswold et al., 1996).
Increased activity in Broca’s area was observed in thesame task under interference conditions that inhibitedthe subvocal rehearsal of sentences (Caplan et al.,2000), as well as in a task with auditorily presented cleft

object vs cleft subject sentences (Caplan et al., 1998).
Another study (Just et al., 1996), noting an increase inactivated voxels in both Broca’s and Wernicke’s areasthat correlated with sentential complexity, concluded
that increased sentential complexity resulted in the recruitment of more neural tissue in each of a network ofcortical areas, with no single region more specificallyinvolved in sentence processing than any other.
Three recent fMRI studies (Dapretto andBookheimer, 1999; Kang et al., 1999; Ni et al., 2000)
have claimed to have evoked differential activity in partof Broca’s area (BA 44) during syntactic as opposed tosemantic processing of sentences or phrases. However,each contrastive experimental condition in these studies
involved both syntactic and semantic processing under
the same task instructions. In neither study was there
any experimental history or independent evidence tosupport the authors’claims about implicit and conflicting task demands across conditions. In addition, different sets of sentences were used for the two conditions,thus involving uncontrolled cognitive factors. These
three studies used ‘implicit’ tasks for both syntactic andsemantic conditions which involve: (i) listening to a pairof sentences to decide whether they have the same
literal meaning (Dapretto and Bookheimer, 1999), (ii)simple reading (Kang et al., 1999), and (iii) listening todecide whether a sentence contained a ‘living thing’ (Niet al., 2000). These task designs lack a control for theapparent attention to syntactic/semantic anomaly anddifference involved. Therefore, it is premature to conclude that these studies dissociate ‘form’ from ‘content’.
Indeed, cortical areas implicated in processing semantic
inforination as opposed to syntactic information areleft BA 47 (Dapretto and Bookheimer, 1999), right BA
10, 45, 46 (Kang et al., 1999), and various other widespread areas in both of the hemispheres (Ni et al.,2000). These conflicting results may stem from themultiplicity of cognitive factors involved in those tasks,
especially in the ‘semantic’ tasks. Moreover, it is notclear whether Broca’s area is activated during ‘explicit’
detection of a syntactic anomaly, which is a key issue inestablishing its involvement in syntactic processing. In
one study with an explicit anomaly detection task, there
was little difference between cortical areas activatedduring syntactic and semantic conditions (Ni et al.,2000).
Given this uncertainty about the role played by
Broca’s area in syntactic processing, we have tried to
identify cortical areas associated specifically with syntactic processing, independent of error detection requiring verbal short-term memory and of error detection ina linguistic context (Embick et al., 2000). We used an
explicit syntactic paradigm with an established experimental history and cognitive theory of the task. Furthermore, the same lexical material was employed
across conditions. Our study combines a version of theK.L. Sakai et al. / Neuroscience Research 39 (2001) 1–10
Table 1
Sample stimuli used in grammar (GR) and spelling (SP) conditions
Error

GR

SP

1

Bill wrote paper a about
the discussion of thetreaty.

Bill wrote a papger about
the discussion of the treaty.

1Mary wanted to readabout the destruction theof city.

Mary waanted to readabout the destruction of the
city.

1

John drove to store the ina very fast car two weeks
ago.

John drove to the store in avery fasvt car two weeksago.

2

Mary asked question a
Mary askepd a question
about theorem the in class. about the theorem in c1lass.

2

The editor read article thewith revisions Anne’s after
lunch.

The editor read the artilcewith Anne’s rezvisions after
lunch.

2

Tom drove the to beachon Will’s fast extremely
motorcycle.

Tom drove to tfe beach on
Will’s extremely fqast
motorcycle.

error-detection paradigm that has been well-exemplified
in ERP studies of syntactic anomaly (Neville et al.,1991), with a linguistic control condition that involves
both normal sentence processing and error detection of
misspelled words, comparable in difficulty to syntactic
error detection. The sentential stimuli use the same
lexical material in English across two conditions ofgrammar (GR) and spelling (SP), and differ only according to the types of errors they contain (Table 1).
Sentences of the GR type contained one or two errors
in word order; sentences of the SP type contained one
or two errors in spelling. In each condition, stimuli
were presented visually, and the task was to determine
whether the sentence contained one or two errors bypressing one of two buttons. By using this one- vs
two-error design, we were able to place stimuli of thesame error-type in blocks, while maintaining a task that
required the processing of each stimulus. In an additional Control (CO) condition, subjects viewed rows ofcolored Ls and Ts, with a basic association between asingle color and a letter; for instance, purple Ts andyellow Ls. In this case, the task was to find matches fora target combination in the upper left-hand comer ofthe screen, where the letter/color violated the basic
pattern; the subject, scanning the further rows of letters, determined whether there was a single match tothis combination, or two matches. Each of the SP and
GR conditions combined linguistic processing with anerror-detection task. The difference between the two
conditions lies in the different types of errors, namely,
grammatical errors, which induce syntactic violations,and spelling errors, which concern orthographic representations. The CO condition controls for both a serial
search and short-term memory of targets.

5

Eight native speakers of English (six male and two
female; foreign students at The University of Tokyo,
Komaba) participated in this study. All the subjects
were right-handed. As to the comparison of behavioral
data between GR and SP, there was no consistentsionificant difference in both RT and accuracy acrossconditions with one error and two errors. We foundthat each of the three cortical language areas, i.e.
AG/SMG, Wernicke’s area, and Broca’s area, showedsignificant increases in signal changes during both GR
and SP tasks, when each condition was compared with
the CO condition (Fig. 4). In addition, the GR condition produced significantly more activation than SP
across language areas. An ANOVA for the left hemisphere (region× condition×block) showed significant
main effects of regions and conditions (PB0.0001), but
no main effect of blocks (P\0.5). Moreover, there wasa significant interaction between regions and conditions(PB 0.05), but there were no other significant interactions (P\0.1). These results suggest that the corticallanguage areas were not uniformly activated under the
GR and SP conditions; rather, there was a clear dissociation among language-related regions. The differential
response between GR and SP was significantly greaterin Broca’s area than in Wernicke’s area, AG/SMG, andthe night homolog of Broca’s area (Fig. 5). One notablefeature of this study is that it did not attempt to isolate
Broca’s area for some task, but that it showed thedifferential contribution of Broca’s area to a welldefined language task.
Given that the task demands were controlled acrossexperimental conditions, these data suggest that Broca’s
area is selectively involved in syntactic processing. They

Fig. 5. A syntactic specialization for Broca’s area. A histogram
comparing the values for percent signal change (mean 9SEM ofsubjects and blocks) for each language condition vs the control(white =SP, black=GR) is shown in each region of interest. Notethe prominent condition difference in the left Broca’s area (L. Broca),
which is larger than in other language areas and than in the righthomolog of Broca’s area (R. Broca) (Embick et al., 2000).

6K.L. Sakai et al. / Neuroscience Research 39 (2001) 1–10

also preclude an interpretation according to which general computational complexity would be the only difference between the GR and SP conditions, as the
behavioral data did not reveal a consistent complexity
contrast between these two conditions. Differences in
activation observed between GR and SP can instead be
attributed to the different linguistic systems involved ineach condition; syntactic error detection in GR, as
opposed to orthographic error detection and normal
syntactic processing in SP. The source of the differences
between GR and SP in Wernicke’s area and AG/SMG
is less clear. It could be that error detection focused in
Broca’s area induces an increase in activation in otherlanguage areas through feedback projections as the
subject attempts reanalysis of the apparently deviant
sentence. It is also possible that a certain amount ofsyntactic processing takes place in Wernicke’s area andin AG/SMG. Finally, although we claim that Broca’s
area is involved in syntactic processing in a particularmanner, we do not make claims about exclusivity;
whether Broca’s area is directly associated with otherlinguistic and/or non-linguistic modules remains an
open question. The involvement of Broca’s area in theprocess of speech production is another issue for future
study (Levelt, 1999). Future work combining electrophysiological and hemodynamic methods will hopefully
clarify the relationship between temporal response components like the LAN/P600 and the activation in Broca’s area observed in this experiment.

3. The modules of phonological and semantic processing
The phonological and semantic aspects of language
processing have been studied primarily at the lexicallevel. A positron emission tomography (PET) study byDémonet et al. (1992) and their subsequent study (Démonet et al., 1994) clearly showed that auditory phonological processing was associated with activation in
Wernicke’s area, whereas semantic processing was associated with activation in the bilateral AG/SMG as wellas in the left prefrontal area (BA 8, 9) and the posterior
cingulate cortex (BA 30, 31). The latter result regarding
semantic processing was obtained by a contrast between a lexico-semantic task for judging attributes inadjective-noun pairs and a phonological task for monitoring phonemes; no significant difference in activation
was found in Broca’s area and in Wernicke’s area. This
result is particularly notable, in that it suggests theexistence of distinct functional modules for phonological and semantic processing. Furthermore, the functional role of AG/SMG and its adjacent areas insemantic processing conforms with that suggested by aprevious lesion study, which showed that pure deficits
in semantic comprehension at the single-word level
were correlated with damage to the left posterior tem-poral and inferior parietal regions (BA 39, 37, 22, and21) (Hart and Gordon, 1990).
On the other hand, there has been significant controversy about the role of AG/SMG and frontal regions in
the lexico–semantic tasks studied with functional imaging techniques. As to the cortical areas that are activated under both auditory and visual conditions, a PET
study with word generation and association tasks suggested the involvement of the left inferior prefrontal
cortex (BA 47) (Petersen et al., 1988, 1989), whereas an
fMRI study with a concrete/abstract judgment tasksuggested the left inferior frontal gyrus (BA 44, 45) andthe bilateral anterior prefrontal cortex (BA 10, 46)(Chee et al., 1999). However, the superior temporal
cortex was not consistently activated in these studies.
The left inferior frontal cortex (BA 45, 46, and 47) was
also associated with semantic category generation andsemantic memory tasks in fMRI studies (Shaywitz etal., 1995; Gabrieli et al., 1996; Crosson et al., 1999).
Another recent fMRI study has reported that phonological processing in a syllable-counting task activatedthe dorsal portion of the left inferior frontal gyrus (BA44, 45), and that semantic processing in a concrete/abstract judgment task activated the ventral portion of theleft inferior frontal gyrus (BA 45, 47) (Poldrack et al.,1999), which is in agreement with previous proposals(Fiez, 1997; Gabrieli et al., 1998).
When these previous studies are considered together,it becomes apparent that the question remains unanswered as to the dependency of cortical responses onprocessing levels of language stimuli (either lexical levelor sentence/discourse level), as well as their dependency
on input modalities (either auditory or visual presentation). Therefore, the delineation of phonological andsemantic processing as well as the exact roles of corticallanguage areas in these processes necessitate carefullyplanned experiments in the near future. The applicationof transcranial magnetic stimulation TMS) may provide
an additional method of overcoming the limits of imaging studies, thereby uncovering the causal link between
cortical activity and the subcomponents of the linguistic
system.

4. Sentence processing in the temporal cortex
There have been an increasing number of neuroimaging studies of sentence processing since a pioneering
PET study by Mazoyer et al. (1993), which showed thatthe left middle temporal gyrus was selectively activatedwhen subjects listened to stories in a native language, ascompared with the condition of listening to semantically anomalous sentences, sentences with pseudowords, a list of words, or story in an unknown
language. These results indicate the selective involvement of the left temporal association areas (Wernicke’s

K.L. Sakai et al. / Neuroscience Research 39 (2001) 1–10

area) in meaningful sentence processing. Another PET
study reported significantly increased activity in the left
superior temporal gyrus (BA 22, 39) and the bilateral
temporal poles (BA 38), when story comprehension
tasks were compared with a condition in which semantically unlinked sentences were presented (Fletcher etal., 1995). Further, the left superior temporal gyrus
showed significant activation when a sentence readingtask was contrasted with the presentation of consonant
strings in an fMRI study (Bavelier et al., 1997). Activation in the posterior part of the left superior and middle
temporal gyri (BA 22, 37) as well as in the bilateral
AG/SMG correlated with linguistic complexity of visually-presented sentences (negative sentences vs. affirmatives) (Carpenter et al., 1999). The left AG was
activated more consistently among tested subjects,
when a task to check the order of actions (presented inphrases) was compared with a task to detect an error in
the word order (Crozier et al., 1999), although thiscomparison involved a variety of other factors such as
motor imagery. Two additional imaging studies(Maguire et al., 1999; St George et al., 1999) reported
activation in the left middle temporal sulcus and thetemporal pole (BA 21, 38), when story comprehension
was enhanced in a paradigm developed by Bransford
and Johnson (1972). Although the exact loci of activated areas were markedly different among these studies with sentence/discourse comprehension tasks, it islikely that a part of Wernicke’s area, AG/SMG, andthe adjacent cortices subserve as a module for sentencecomprehension or semantics. This module would becomplementary to Broca’s area as a syntactic module.
The individual roles of Wernicke’s area and AG/SMG
should be clarified by future studies.
To address the issue of sentence processing in the
cerebral cortex further, we adopted several new approaches in our recent study using Optical Topography(OT) (Sato et al., 1999). First, we compared two conditions, namely, listening to successive sentences of astory and listening to repeated sentences. The lattercondition subserved as a control for basic sentence
processing. Second, we used a dichotic listening taskthat required intensive tracking of speech sounds. In aprevious fMRI study, we compared a similar paradigm
with a diotic (binaural) listening control, and foundthat subregions of the auditory and language areas
show enhanced activity during the dichotic listening
condition (Hashimoto et al., 2000). That fMRI study isparticularly notable in that it agrees with a previous
anatomical study by Rivier and Clarke (1997) withrespect to the anatomical location of these areas andthe order of the proposed hierarchical levels. Such
research will enhance the understanding of both structural and functional bases of language information
processing. Third, we used a recently developed noninvasive imaging technique, OT, which measures tempo-

7

ral changes in hemoglobin oxygenation simultaneously
at multiple regions (Maki et al., 1995; Yamashita et al.,
1996; Koizumi et al., 1999). OT is a new extension ofnear-infrared spectroscopy (NIRS) for acquiring a topographical image; NIRS measures spectroscopic
reflection and scattering at a single region with a lightemitter and a detector (Chance et al., 1993; Hoshi andTamura, 1993; Kato et al., 1993; Villringer et al., 1993).
There are several advantages of using OT over otherfunctional mapping techniques. First, it is possible toindependently measure the temporal changes in oxyhemoglobin concentration (Coxy) and deoxyhemoglobin
concentration (Cdeoxy). Second, there is no scanningnoise to interfere with the experimental auditory stimuli. Third, its signal-to-noise ratio is relatively high,allowing for the observation of cortical activity with asmall number of trials. One major disadvantage of OT
is that its measurement is restricted to the corticalsurface. Nevertheless, OT has the potential to introduce
a new dimension to the mapping of human cognitive
functions.
In our OT study, we measured the local changes innear-infrared light absorption simultaneously from 44
points in both hemispheres. The measured region ineach hemisphere centered on the Sylvian fissure andcovered an area of 6× 12 cm2. Target stimuli andnon-target stimuli were simultaneously presented to
opposite ears every 2 s, and a target was alternatively
presented to either the left ear or the right ear at
random intervals. Subjects were asked to track targets
and to press a button when targets shifted from one ear
to the other. We tested: (i) a control task, in which atone and white noise were presented as targets andnontargets, respectively, (ii) a repeat task, in which thetarget was one repeated sentence within a task block,and (iii) a story task, in which the targets were successive, different sentences of a continuous story. In therepeat and story tasks, target sentences were read inJapanese, and non-targets were prepared by scrambling
the sequence of syllables of the correspondent target. A
sentence different from the target for the repeat task
and contextually anomalous phrases for the story task
were used as probe stimuli. Therefore, these tasks could
not be completed appropriately by identifying speechsounds without paying attention to their meanings, andthey were equally balanced in terms of behavioral control for task difficulty. Seven male native speakers ofJapanese participated in this study. All the subjects
were righthanded. The results of this study are relevantto the cortical activity of native speakers confronted
with their own language.
We observed left-dominant activation in the superior
temporal cortex (the superior and middle temporalgyn), preferentially during the story task over the repeat
task when compared with the control task (Fig. 6).
Wider regions were clearly more activated during the8

K.L. Sakai et al. / Neuroscience Research 39 (2001) 1–10

Fig. 7. Focal activation in the left superior temporal cortex during sentence processing. OT images in r-maps for a direct comparison between
story and repeat tasks. Left, r-maps of Coxy temporal changes; Right, r-maps of Cdeoxy temporal changes. Activation is localized in the middle
temporal gyrus in both comparisons.
Fig. 8. Hemodynamics in speech-recognition tasks relative to the control task. (A) Story and control tasks; (B) Repeat and control tasks. There
were three periods of either the story task (S) or the repeat task (R) in each run. Red lines show the mostly positive temporal changes of Coxy,whereas the blue lines reveal the mostly negative temporal changes of Cdeoxy. These temporal changes were calculated from averaged data among
subjects.

story task than during the repeat task in both hemispheres. This finding is consistent with the results of aprevious PET study that showed activation of the left
superior temporal conex when subjects listened to continuous speech in their native language (Mazoyer et al.,1993). The direct comparison between the hemodynamics in the story task and that in the repeat task showed
focal activation in the left superior temporal cortex(Fig. 7). Both an increase in Coxy and a decrease in
Cdeoxy were significantly larger in the middle temporalgyrus than in the superior temporal gyrus. The temporal changes in the left superior temporal cortex are
shown in Fig. 8. With a delay of 6 s, an increase in Coxywas synchronized with each onset of the story task, andafter reaching a plateau, Coxy returned to the baseline
level at the end of the task. Although a decrease inK.L. Sakai et al. / Neuroscience Research 39 (2001) 1–10

Cdeoxy was also synchronized with each period of thestory task, Cdeoxy did not exactly mirror the temporal
dynamics of Coxy. This result indicates that the temporal changes in Coxy. and Cdeoxy may reflect different
physiological processes whose temporal dynamics arecorrelated over the long term ( ~ 30 s) but are different
in the short term ( B 10 s). Similar, but smaller, changes
in both Coxy. and Cdeoxy were observed in the repeat
run. These results suggest that the hemodynamics in the
mid-lateral part of the left temporal cortex reflect cognitive factors involved in the processing of sentences. A
critical difference between the story and repeat tasks
would be the load of speech stimuli to be processed.
Recognition of successive different sentences of a story
demands more auditory, memory, and language information processing than the recognition of repeatedsentences. The temporal cortex activation reported here
is also consistent with the role of the primate temporal
association area in memory storage and memory retrieval (Sakai and Miyashita, 1993; Sakai et al., 1994).

5. Conclusion
Based on converging evidence from aphasic andimaging studies, we propose a modular specialization of
Wernicke’s area, AG/SMG, and Broca’s area, which is
directly related to phonological, semantic, and syntactic
processing. Further, the left inferior frontal regions are
involved in some aspects of phonological and semantic
processing, whereas the left middle temporal regions are
critical for sentence processing. This rather broad delineation at the current stage of imaging studies reflects
the difficulty of dissociating linguistic components from
confounding cognitive factors. The language systemdoes not stand alone but interacts with other systems ofperception, memory, and consciousness, as well as withthe speech output system. Future work combining electrophysiological (ERP, MEG), hemodynamic (PET,
fMRI, OT), and magnetic stimulation (TMS) methods
will allow us further parcellation of language processingin the cerebral cortex and will enable us to addressquestions about module-specific brain areas and how
they actually perform linguistic computations.

Acknowledgements
We would like to thank Dr Yasushi Miyashita for his
encouragement, Dr David Embick, Dr Alec Marantz,
Dr Wayne O’Neil, Mr Hiroki Sato, and Mr Tatsuya
Takeuchi for collaborating in fMRI and OT experiments, and Ms Hiromi Matsuda for her administrative
assistance. This work was supported by a CREST grantfrom JST and a grant from Toyota Physical and Chemical Research Institute to KLS.

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