Correlated Functional Changes of thePrefrontal Cortex in Twins Induced byClassroom Education of Second Language

As the neural substrates of second language (L2) acquisition arelargely unknown, they may or may not be similar to those of first
language (L1) representation. We used functional imaging to
examine whether training in the conjugation of English verbs frompresent to past tense alters brain activations in 13-year-old twins. A
novel experimental design contrasted past tense verb identificationand verb matching, which were tested in either English (L2) orJapanese (L1). After 2 month classroom training in the past tenseusing bingo games, the two individuals in each pair exhibited significantly correlated performances. When pre- and post-scanningsessions were compared with each other for L2, the left dorsal
inferior frontal gyrus (IFG) exhibited significantly correlated activation increases within each pair of twins and the increases were positively correlated with individual performance improvements.
Moreover, the cortical plasticity for L2 acquisition was guided
toward the L1 specialization of the left dorsal IFG, in spite of notabledifferences between L1 and L2 in the students’ linguistic knowledge
and in their performance in making past tense forms. These findings
suggest a cortical mechanism underlying L2 acquisition, which critically depends on shared genetic and environmental factors for eachtwin in a surprisingly predictive manner.
Keywords: functional imaging, grammar, inferior frontal gyrus, language
acquisition, past tense

Kuniyoshi L. Sakai1,2, Kunihiko Miura2,3, Nobuko Narafu2,3
and Yukimasa Muraishi2,31Department of Cognitive and Behavioral Science, Graduate

School of Arts and Sciences, University of Tokyo, Komaba, 38-1 Komaba, Meguro-ku, Tokyo, Japan, 2CREST, Japan Scienceand Technology Agency, Kawaguchi-shi, Japan and 3The
Secondary Education School Attached to the Faculty of
Education of the University of Tokyo, 1-15-1 Minamidai,
Nakano-ku, Tokyo, Japan

studying English for the first time at a secondary education
school in Japan. We targeted twins as subjects, because it is
intriguing to ask whether shared factors of twins actually influence their language abilities and neural substrates for Japanese(L1) and English (L2). For 2 months, the students participatedin intensive training in English verbs as part of their standard
classroom education (see Materials and Methods). All first-year
students (n = 117) in three classes received the training and inno case did both members of a twin pair belong to the sameclass. To evaluate directly the brain’s changes in activation due
to this training, the twins completed two sets of functional
magnetic resonance imaging (fMRI) sessions, one before thetraining (day 1) and one after the training (day 2). Figure 1 illustrates the experimental paradigm with four tasks used in fMRI
sessions: an English verb-matching (EM) task, an English pasttense (EP) task, a Japanese verb-matching (JM) task and a Japanese past tense (JP) task. There were two EP task blocks in asingle fMRI session: one block (EPr) with seven regular verbs
and one irregular verb (at a randomized position) and the other(EPi) with seven irregular verbs and one regular verb. General
cognitive factors such as word recognition and response selection were controlled by the EM and JM tasks, which weredirectly compared with the EP and JP tasks, respectively. A
particular challenge in this study was to assess the effect of an
educational method used in classroom lessons directly in termsof brain activation.

Introduction
The native or first language (L1) is normally acquired in thefirst several years of life, during which children rapidly expand
their linguistic knowledge (Boysson-Bardies, 1999; Gopnik etal., 1999). In contrast, a second language (L2) can be masteredat any time in life, though the L2 ability becomes rarely
comparable to L1 if it is acquired beyond the hypothesized critical period around puberty (Lenneberg, 1967; Johnson and
Newport, 1989). Whether L2 relies on the same dedicatedmechanism of L1, which may be arguably universal grammar, isthus a matter of debate (Epstein et al., 1996). It has been
recently reported that L1 and L2 are represented differentiallyin cortical areas during discourse production or listening tasks(Dehaene et al., 1997; Kim et al., 1997). However, otherimaging studies have reported common neural substrates of L1and L2 during word generation tasks (Klein et al., 1995; Cheeet al., 1999). The critical experiments thus would be to clarify
brain plasticity that represents new acquisition of L2, i.e. thedynamic processes of L2 acquisition and associated corticalchanges, rather than static states that reflect a certain level ofL2 performance.
In the present study, we examined whether the learning ofEnglish past tense verbs (64 regular and 64 irregular verbs) as
L2 knowledge alters brain activations for first-year students

Materials and Methods

Cerebral Cortex V 14 N 11 © Oxford University Press 2004; all rights reserved

Cerebral Cortex November 2004;14:1233–1239; doi:10.1093/cercor/bhh084

ParticipantsParticipants in the present fMRI study were 18 native Japanese
speakers (11 females and 7 males, all aged 13) without any neurological problems. They consisted of seven monozygotic and two
dizygotic twin pairs, as determined by serological analyses of blood
types and DNA markers. All subjects showed right-handedness (laterality quotients: 44–100) according to the Edinburgh inventory. One
dizygotic twin pair had lived in the United States from age 7–9 withEnglish exposure and thus the data on this pair were excluded fromthe analyses. None of the other pairs had learned English past tenseverbs before the present training. The participants were in a supine
position in the magnet, while the participant’s head was immobilizedwith padding inside the radio-frequency coil. The data from one
monozygotic twin pair were not included in the analyses because ofhead movements during scanning. The current results thus based onseven twin pairs (eight females and six males). Informed consent was
obtained from all twin individuals and their parents. This study wasapproved by the Secondary Education School Attached to the Facultyof Education of the University of Tokyo and by the institutional review
board of the University of Tokyo, Komaba.
Tasks
In each 3 s trial of the fMRI experiments, word or pseudoword stimuli
in yellow letters against a dark background were presented visually at

Figure 1. The four language tasks used in the functional imaging sessions. (A) English verb-matching (EM) task (‘E’). (B) English past tense (EP) task (circled ‘E’). (C) Japaneseverb-matching (JM) task (‘J’). One example (tsukamu; gloss: catch) is shown. (D) Japanese past tense (JP) task (circled ‘J’). For this example, the one on the left (tsukannda; gloss:caught) is correct. Japanese stimuli were presented in both the hiragana and kanji writing systems and were matched with English words of the same meaning. For fixation, a red
cross was always shown at the center of the screen, but it was omitted from the stimuli. See Materials and Methods for details of each trial.
the center of the screen (Fig. 1). First, a symbol of ‘E’ (EM), circled ‘E’(EP), ‘J’ (JM) or circled ‘J’ (JP) was shown for 400 ms at the initiationof every trial, indicating the task to be performed. Next, a present
tense verb was shown for 1300 ms, during which the subject read itsilently for EM and JM, or read its past tense form silently for EP and JP
if they knew it (otherwise, they read the presented verb). Finally, twochoice stimuli were presented for 1000 ms and the subjects chose thesame present tense verb for EM and JM, or chose the correct pasttense form for EP and JP even if it was unfamiliar to them, by pushing
one of two buttons. The time limit given for responses was as short as1000 ms, so that responses without preplanning were discouraged.
No feedback on performance was given to any subject.
The four tasks were conducted in a block design and the stimuli
used in each block were different. Six trials were tested in each EM
block and eight trials were tested in each block for the other tasks.
The EM task served as the baseline; one EM block and one block eachof JM, EPr, EPi and JP were alternately presented (a total of nine
blocks) for each fMRI session. Ten fMRI sessions were carried out in
one day. The order of tasks was counterbalanced across subjects. The
stimulus presentation and behavioral data collection were controlled
by LabVIEW software and interface (National Instruments, Austin,
TX). The subjects wore earplugs and an eyeglass-like MRI-compatible
display (resolution: 800 × 600, VisuaStim XGA; Resonance Technology
Inc., Northridge, CA). The same stimuli and tasks were used on days 1
and 2 to equalize any material-dependent conditions except practiceeffects.
Training
For each classroom lesson, two bingo sheets (a 5 × 5 matrix on each
sheet, with rows B, I, N, G and O as well as a ‘free’ square in thecentre) were prepared. The first sheet contained a list of eight verb
pairs matching present tense of a verb to the past tense (e.g.
close–closed), while the second sheet contained eight past tenseverbs only. Before each lesson began, the students were asked tocomplete these sheets by filling in each row with five of eight verb
items, one item per square. During the game with the first sheet, theteacher called out each row’s name (circularly in the order of B, I, N,
G and O) and any verb pair; each student then marked the square ofthat row in which the called verb pair had been already written.
‘Bingo!’ is announced by the student when one row, column, or diagonal line of five squares has been marked. The first game continues
until one student announces ‘Bingo! Bingo!’ when all squares aremarked. During the game with the second sheet, the teacher calledout each row’s name and any present tense verb and each student
then marked the square of that row in which the corresponding pasttense verb had been already written. The purpose of the second
game is to conjugate English verbs from present to past tense. It
takes ∼5 min to complete these two games.

1234 Prefrontal Cortex Changes during Second Language Education • Sakai et al.

A set of 64 verbs with regular inflection and a set of 64 verbs withirregular inflection were prepared and they were grouped on 16 bingo
sheets as follows: for class A, either regular or irregular verbs withsimilar sound patterns (e.g. ‘bring–brought’ and ‘think–thought’)
were grouped together; for class B, either regular or irregular verbs
were grouped, while verbs with different sound patterns were mixed
together; and for class C, all verbs were grouped randomly. Fromthese sets, we chose 48 verbs (24 regular and 24 irregular) for thefMRI sessions and 50 verbs (25 regular and 25 irregular) for an English
past tense examination. Through the 2 month period, each class had
25 lessons, going through the nine bingo sheets twice. The original
method of using bingo games in class to teach English words wasdeveloped by Mr Katsuhiko Osa.
fMRI Data Acquisition and Analyses
The fMRI scans were conducted using a 1.5 T scanner (Stratis II,
Premium; Hitachi Medical Corporation, Tokyo, Japan). Using a
gradient-echo echo-planar imaging sequence (repetition time, 3 s;echo time, 50.5 ms; acquisition time, 1850 ms; resolution, 3 × 3 mm2),
we scanned 16 horizontal slices, each 6 mm thick and having a 1 mm
gap, covering from z = –49 to 62 mm. We performed group analyses
using SPM99 statistical parametric mapping software (Wellcome
Department of Imaging Neuroscience, London, UK). We realigned thefunctional volume data in multiple sessions and removed sessions that
included data with a translation of >2 mm in one of the three directions and a rotation of >1.4°. The data were normalized to the standard
brain, resampled every 3 mm using bilinear interpolation andsmoothed with an isotropic Gaussian kernel of 12 mm full width at
half maximum. Task-specific effects were estimated with a generallinear model using a boxcar waveform convolved with the canonicalhemodynamic response function. Random effects analyses were
performed for all of intersubject comparisons. The statistical parametric maps in each comparison were thresholded at corrected P <0.05 for the cluster level and uncorrected P < 0.001 for the voxel level.
Statistical significance of positive correlation between the two individuals in each twin pair was tested using Spearman rank correlation(one-sided), which is resistant to outliers, i.e. high leverage points.

Results
By the end of training, the students showed significant
improvements in identifying the correct English past tenseverbs, as assessed by past tense examination in class. The same
examination was administered without consultation before
and after the 2 month training period. Given a verb in thepresent tense (e.g. ‘bring’), the students marked which of two
possible past tense verb forms (e.g. ‘brought’ or ‘bringed’) wascorrect. For present tense verbs that seemed unfamiliar, thestudents were instructed not to mark either of the two pasttense forms. The mean scores of the first and second examination for all 117 students were 14 ± 3.4% and 61 ± 2.9% (mean ±SE), respectively. There was no statistically significant difference in examination scores among the three classes (P > 0.1).
The seven twin pairs (n = 14) also showed better scores forthe second examination: regular verbs, 64 ± 5.7%; and irregularverbs, 55 ± 6.4%. There was no significant difference between
the scores of regular and irregular verbs [paired t-test, t(13) =1.3, P > 0.2] and thus the score data were collapsed. The two
individuals in each pair exhibited marginally correlated
performances on the second examination (r = 0.69, Spearman
rank correlation coefficient rS = 0.62, P = 0.06; Fig. 2A), in spiteof large interpair differences in performance improvements. In
order to establish that this correlation within each pairoccurred not by chance but due to factors that individual twins
had in common with their counterpart twins within a pair,each individual was randomly assigned to a new pair toproduce >100 permutations. These random pairings resulted in
the normal distribution with mean r = 0.0 and SD = 0.40. Therefore, the above correlation coefficient of r = 0.69 reaches statistical significance at P < 0.05 (Z > 1.64).
The accuracies of the seven twin pairs for EM, JM and JP, performed during fMRI sessions, was 90, 95 and 91%, respectively,

Figure 2. Significant correlation for performances on past tense verbs within each pairof twins. (A) The score of an English past tense examination is plotted for each pair oftwins (identified as twin A and twin B). Open and filled dots denote data on day 1(before training) and day 2 (after training), respectively. (B) The accuracy for the EP
tasks in fMRI sessions on day 2 is plotted for each pair of twins. A regression line forday 2 data is shown for each panel.

all of which remained unchanged for days 1 and 2. According
to an analysis of variance (ANOVA) with two variables [task(EM, JM and JP) × day (days 1 and 2)], accuracy data showedsignificant main effects of task (P < 0.0005), while the main
effects of day and their interactions were not significant (P >0.05). In the EP tasks, forced two-choice were imposed even if
present tense verbs seemed unfamiliar, and the students chose
verbs with incorrect regular inflections (e.g. ‘selled’ rather
than ‘sold’) more often than those with incorrect irregularinflections (e.g. ‘smold’ rather than ‘smelled’, in analogy with‘sell’–‘sold’). For day 1, the mean accuracies for the past tense
forms of regular verbs (seven stimuli in EPr and one in EPi) andthat for irregular verbs (seven stimuli in EPi and one in EPr)
were 79 ± 3.9 and 22 ± 3.9%, respectively (51 ± 1.0% on average); for day 2, they were 77 ± 3.7 and 43 ± 6.3%, respectively(60 ± 1.9% on average). An ANOVA on these accuracy data confirmed the significant interaction of verb type by day (P < 0.05).
The unusually high accuracy for regular verbs was probably
due to mere guesswork of choosing verbs ending in ‘-ed’
when past tense verbs cannot be recalled with confidence. The
individuals within the twin pairs were highly correlated witheach other in their overall performances of the EP tasks for day
2 (r = 0.71, rS = 0.79, P < 0.025; Fig. 2B). The permutation
procedure, which resulted in the normal distribution withmean r = 0.0 and SD = 0.39, also confirmed statistical significance at P < 0.05.
In parallel with the performance improvements for English
past tense verbs, we observed clear activation increases incortical regions (Fig. 3 and Table 1). When EPr blocks were
contrasted with EM blocks in a random effects analysis for day
2, major activations were found in the following regions: thedorsal region of the left inferior frontal gyrus (IFG) spanning
the opercular part and the triangular part of IFG (F3op/F3t),
the left F3t/F2 [Brodmann’s area (BA) 46] and the right cerebellum (lobule VI, extending to Crus I; Fig. 3A and Table 1). Allof these activations were absent in EPr – EM for day 1.
Although the apparent performance for regular verb inflectionwas ∼80% for both days 1 and 2, the almost pure guesswork
involved in choosing verbs ending in ‘-ed’ for day 1 did not
sufficiently induce this activation. When EPi blocks were
contrasted with EM blocks for day 2, significant activations
were observed in the following regions: the left dorsal IFG(F3op/F3t), the left ventral IFG spanning the triangular partand the orbital part of IFG (F3t/F3O), the left F3t/F2 (BA 46),
the left angular gyrus and supramarginal gyrus (AG/SMG) andthe right cerebellum (Fig. 3B and Table 1). All of these activations were absent in EPi – EM for day 1. It may be notable thatthe activated regions of the left IFG for day 2 in EPi – EM wereslightly wider than those in EPr – EM (Table 1) and that the left
AG/SMG activation was observed only in EPi – EM. However,the direct comparison EPi – EPr showed no significant activation for day 2.
Given the consistency of activations between the EPr and EPi
blocks, we performed a paired t-test of day 2 – day 1 as asecond level analysis of (EPr + EPi) – EM. This random effects
analysis resulted in a single activated region of the left dorsal
IFG (Fig. 3C and Table 1). Moreover, the JP – JM contrast for
day 2, with the same statistical analyses as used in EPr – EM and
EPi – EM, revealed the left IFG activation that extends fromdorsal (F3op/F3t) to ventral (F3t/F3O) regions (Fig. 3D and
Table 1). This left IFG activation was stable and remained
unchanged between days 1 and 2, in that a paired t-test of

Cerebral Cortex November 2004, V 14 N 11 1235

Figure 3. The neural systems for processing L1 and L2 past tense verbs. The activated regions were projected onto a surface-rendered standard brain. (A) EPr – EM for day 2. (B)EPi – EM for day 2. The most prominent activation change was observed in the left (L) inferior frontal gyrus (IFG). (C) A paired t-test of day 2 – day 1 as a second level analysis of(EPr + EPi) – EM. (D) JP – JM for day 2.

Table 1
Cortical regions involved in English and Japanese verb tasks
BA

Side

x

F3op/F3t

44/45

L

–51

27

F3t/F2

46

L

–48

42

Precentral gyrus

6

R

51

F1M

6

M

–3

Cerebellum

–

R

27

F3op/F3t

44/45

L

F3t/F3O

45/47

L

F3t/F246

AG/SMG
Cerebellum

Brain regionyzCluster size

Z-value

27

386

4.8

–3

115

4.2

6

27

62

4.0

24

51

71

3.8

–69

–27

157

3.7

–45

21

30

478

4.9

–33

27

–3

164

4.9

L

–45

48

0

57

3.8

39/40

L

–30

–66

39

303

4.4

–

R

12

–93

–6

230

4.0

44/45

L

–51

24

24

88

4.0

44/45

L

–54

9

18

395

4.2

21

L

–63

–45

0

109

4.3

EPr – EM (day2)

EPi – EM (day2)(EPr + EPi) – EM (day2 – day1)
F3op/F3t
JP – JM (day2)
F3op/F3t
JM – EM (day2)
MTG

Stereotactic coordinates (x, y, z) in the standard brain space (mm) as defined by Montreal Neurological Institute (MNI) are shown for each local maximum of Z-values in the contrasts indicated. BA,
Brodmann’s area; L, left; R, right; M, medial; F3op, inferior frontal gyrus, opercular part; F3t, inferior frontal gyrus, triangular part; F3O, inferior frontal gyrus, orbital part; F2, middle frontal gyrus; F1M, superior
frontal gyrus, medial; AG/SMG, angular gyrus and supramarginal gyrus; MTG, middle temporal gyrus.

day 2 – day 1 as a second level analysis of JP – JM showed nosignificant activation. It is thus striking to note that the left
prefrontal regions activated for the English past tense verbs

1236 Prefrontal Cortex Changes during Second Language Education • Sakai et al.

exactly match the regions activated for the Japanese past tenseverbs. Indeed, the conjunction analysis of (EPr + EPi) – EM and
JP – JM revealed significant activation only in the left dorsal IFG

(cluster size, 56 voxels). These results suggest that the activation increases in the left dorsal IFG represent the acquisition of
past tense knowledge.
We next examined whether or not shared factors of twins
influence the functional changes observed here. Consistent
with the correlated performances for the past tense examination and the EP tasks, the activation increases at one local
maximum (–45, 21, 30) of the left dorsal IFG (F3op/F3t),
which were calculated for (EPr + EPi) – EM across days 1 and 2(0.21 ± 0.04%; mean ± SE), showed a highly significant correlation within each pair of twins (r = 0.80; rS = 0.79, P < 0.025)(Fig. 4A). The permutation procedure, which resulted in thenormal distribution with mean r = 0.0 and SD = 0.39, also
confirmed statistical significance at P = 0.02. The activation
changes of the same region in JP – JM across days 1 and 2 (0.05± 0.06%, i.e., no significant change) showed no positive correlation within each pair of twins (r = –0.46), indicating that thesignificant correlation is selective to L2 acquisition. In contrast,
the activation change at one local maximum (27, –69, –27) of
the right cerebellum, which were also calculated for (EPr + EPi)
– EM across days 1 and 2, showed no significant correlation(r = –0.017), and the activation was more variable among individuals (Fig. 4B). It is thus surprising that functional changes
specifically observed in the left dorsal IFG are influenced by

Figure 4. The region-specific correlated activation increases for L2 within each pair oftwins. (A) The activation increases (∆signal change: day 2–day 1) of the left dorsal IFG(–45, 21, 30) in (EPr + EPi) – EM, plotted for each pair of twins (identified as twin A
and twin B). (B) The activation changes of the right cerebellum (27, –69, –27) in (EPr
+ EPi) – EM across days 1 and 2. A regression line is shown for each panel.

shared factors for each pair of twins in a highly predictive
manner.
Finally, we tested whether or not the activation increases in
the left dorsal IFG predicted the extent to which each individual subject improved his/her knowledge of the past tense.
We found a significant positive correlation (r = 0.63, Fisher’s r
to Z transformation Z = 2.5, P < 0.02, two-sided) between the
improvements in examination scores and the activation
increases in (EPr + EPi) – EM across days 1 and 2 (Fig. 5). Therefore, we conclude that the amount by which activation
increases in the left dorsal IFG is a good indicator of individual
improvement in acquiring L2 past tense knowledge.

Discussion
The results are striking in three ways. First, after classroom
training in past tense verbs in L2, each 13-year-old twin pair
exhibited significantly correlated performances for both thepast tense examination and the EP tasks. Secondly, the left
dorsal IFG exhibited significantly correlated activation
increases within each pair of twins and the increases werepositively correlated with individual performance improvements. These results suggest that the functional changes specifically observed in the left dorsal IFG are susceptible to shared
genetic and environmental factors for each twin in a surprisingly predictive manner. Thirdly, the cortical plasticity for L2
acquisition was guided toward the L1 specialization of the left
dorsal IFG, observed at least at the age of 13, in spite of notabledifferences between L1 and L2 in the students’ linguisticknowledge and in their performance in making past tense
forms. The present fMRI study thus successfully elucidates one
type of cerebral mechanisms underlying language acquisition,
indicating how new linguistic knowledge is acquired andrepresented in individual brains. To our knowledge, thepresent study is the first direct demonstration that classroom
education, if properly executed, can change the function of
the prefrontal cortex.
The left IFG activation observed for the EP tasks on day 2 andfor the JP task on both days cannot be explained by taskdifficulty or other domain-general factors, because the EP
tasks were easier on day 2 than on day 1 and the JP task wasmuch easier for the subjects. We have recently established

Figure 5. Significant correlation between L2 performance improvements andactivation increases in the left dorsal IFG. For all individual participants (n = 14), theactivation increases (∆signal change: day 2–day 1) of the left dorsal IFG (–45, 21, 30)
in (EPr + EPi) – EM are plotted against improvements in examination scores (∆score:day 2–day 1). A regression line is shown.

Cerebral Cortex November 2004, V 14 N 11 1237

that the left IFG is selectively involved in syntactic processes
and that its function is indeed separable from domain-general
cognitive factors such as task difficulty and short-term memory(Hashimoto and Sakai, 2002; Sakai et al., 2002, 2003; Suzuki
and Sakai, 2003). We also excluded the possible involvementof familiarization in discriminating and choosing real words
over nonwords. If such a general factor had resulted in the left
IFG activation for the EP and JP tasks, the EM and JM tasks
would have produced comparable activation, and thus neither(EPr + EPi) – EM nor JP – JM would have shown any activation.
Moreover, the left IFG activation is independent of reading
skills and semantic processes associated with presented verbs.
The contrast between the two language tasks JM – EM would
extract highly developed reading skills and semantic processesof L1, but this contrast resulted in significant activation of theleft middle temporal gyrus (MTG) alone (Table 1). Furthermore, the absence of significant activation in a paired t-test of
day 2 – day 1 as a second level analysis of JP – JM ruled out
general practice effects associated with performing the sametasks twice, as well as normal brain development that occurs instudents over a two-month period. The right cerebellum activation observed in EPr – EM and EPi – EM for day 2, but not in JP– JM, is consistent with its transient role in practice-related
learning (Raichle et al., 1994).
The English past tense debate has been a major issue in cognitive science, focusing on the role of grammatical rules and/or
associative memories in acquiring knowledge of the past tense(Chomsky and Halle, 1968; Rumelhart and McClelland, 1986;
Pinker, 1991; Marslen-Wilson and Tyler, 1997). One positronemission tomography (PET) study (Jaeger et al., 1996) reports
activation of widespread cortical regions for past tense generation, but data have not been conclusive as to the regular/
irregular verb distinction. This is because task difficulty may
account for the differences in brain activation. The present
study contributes to this debate from a cross-linguistic point ofview, comparing the identification of Japanese (L1) and English(L2) past tense verbs. We suggest that syntactic mechanisms,
rather than domain-general associative mechanisms, may be
crucial in identifying past tense verbs. There are two reasonsfor this suggestion. First, Japanese past tense forms basicallyfollow several sets of morphosyntactical rules (Tsujimura,1996). Acquiring English morphosyntax as L2 involves not only
the explicit knowledge of placing ‘-ed’ at the end of verbs, butalso the knowledge of exceptional rules, such that some verbs
do not end in ‘-ed’; an exception thus proves the rule even for
irregular verbs. Secondly, neuroimaging studies have accumulated the evidence for the syntactic specialization of the left
IFG (Stromswold et al., 1996; Embick et al., 2000; Friederici etal., 2000; Hashimoto and Sakai, 2002; Sakai et al., 2002),
though more work is still needed for language development.
The present study further demonstrates that appropriate L2
training guides brain function toward L1 specialization. Futurestudies with substantial numbers of monozygotic and dizygotic
twins at various ages will clarify whether genetic or environmental factors are responsible for the behavioral and functionalchanges observed here. Our approach to evaluate educational
methods in terms of not only indirect behavioral changes but
direct functional changes takes a first step toward a new era in
the brain science of education.

1238 Prefrontal Cortex Changes during Second Language Education • Sakai et al.

Notes
We thank Yoshiki Hotta for initial guidance in the twin studies; Masao
Ito and Yasushi Miyashita for their encouragement and helpful suggestions; the twin study group of researchers at Graduate School of
Medicine, University of Tokyo for their zygosity analyses; Toshio
Mitsuhashi, Kazuyoshi Hirano, Masako Fukushima, Yasuo Tanabe,
Akiko Katsumata and Yuko Sugiura for their help in the twin studies;
Kei Suzuki, Satoshi Suo, Natsuki Saeki, Ryuichiro Hashimoto andYoshinori Tatsuno for their technical assistance; and Minako Makifor administrative assistance. This study was supported by a Core
Research for Evolutional Science and Technology (CREST) grant fromthe Japan Science and Technology Agency (JST) and by a Young
Investigators’ Grant from the Human Frontier Science Program (HFSP)
to K.L.S.
Address correspondence to Kuniyoshi L. Sakai, Department of
Cognitive and Behavioral Science, Graduate School of Arts andSciences, University of Tokyo, Komaba, 3-8-1 Komaba, Meguro-ku,
Tokyo 153-8902, Japan. E-mail: sakai@mind.c.u-tokyo.ac.jp.

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