Neuroscience & Medicine, 2010, 1, 64-70
doi:10.4236/nm.2010.12010 Published Online December 2010 (http://www.SciRP.org/journal/nm)
Lateralization of Receptive Language Function
Using near Infrared Spectroscopy
Natacha Paquette 1,2, Berta Gonzalez-Frankenberger 1,2, Phetsamone Vannasing 1, Julie Tremblay 1,
Olivia Florea 1,2, Renée Beland 1,2, Franco Lep ore 1,2, Maryse Lassonde 1,2
1Centre de Recherche, University Hospital Center Sainte-Justine, Montreal, QC, Canada; 2Centre de Recherche en Neuropsychologie
et Cognition, Université de Montréal, Montréal, QC, Canada
Received September 1st, 2010; revised September 8th, 2010; accepted September 13th, 2010
ABSTRACT
In recent decades, functional magnetic resonance imaging (fMRI) has proven to be more effective than the Wada test in
the evaluation of language lateralization in special populations such as epileptic patients and children. However, fMRI
requires that subjects remain motionless during data acquisition, making the assessment of receptive and expressive
language difficult in young children and population with special needs. Near-Infrared spectroscopy (NIRS) is a non-
invasive technique that has proven to be more tolerant to motion artifacts. The aim of the pr esent study was to investi-
gate the use of NIRS to assess receptive language patterns using a story listening paradigm. Four native French-speake rs
listened to stories read aloud by a bilingual speaker in both French and Arabic. To determine if the signal recorded was
affected by episodic memory processes, a familiar story and an unknown story were presented. Results showed that
listening to stories in French elicited a significantly h igher left lateralized response than listening to stor ies in Arabic,
independently of the familiarity of the story. These results confirm that NIRS is a useful non-inva sive technique to assess
receptive language in adults and can be used to investigate language lateralization among children and epileptic pa-
tients slated for epilepsy surgery.
Keywords: Language Lateralization, Near Infrared Spectroscopy (NIRS), Optical Imagi n g, Brain Mapping , E pi l epsy
1. Introduction
Pre-surgical examination of epileptic patients traditionally
includes language lateralization assessment [1]. However,
language is a complex en tity involving multiple levels of
processing. Expressive language tasks (e.g. verbal flu-
ency) are the most frequently used paradigms to investi-
gate language latera lization [2,3]. Receptive language pa ra -
digms, however, may be more suitable when working
with young children or patients with mental retardation
as they do not require active participation of the subject
[4]. A number of functional magnetic resonance imaging
(fMRI) and positron emission tomography (PET) studies
suggest a left temporo-frontal stream specifically involved
during syntactic and semantic processing, both necessary
to comprehension [5-7]. For instance, the processing of
sentence with canonical Subject-Verb-Object structure
(SVO) involves a pathway that includes the frontal infe-
rior gyrus, the supplementary motor area and the tempo-
ral inferior gyrus [8]. These authors further suggest that
the left temporal inferior gyrus would play a role in the
integration of the Subject, the Verb and the Object into a
semantically coherent sentence.
It thus appears that the integration of acoustic, seman-
tic and syntactic processes is necessary for language
comprehension [9]. Therefore, studies aiming to localize
receptive language must rely on language tasks requiring
integration of information processed in theses modules,
such as coherent sentences or story comprehension tasks.
Using fMRI, Schlosser, Aoyagi, Fulbright, Gore & M cC arthy
(1998) observed a stronger activation of the left superior
temporal sulcus compared to the right homologous re-
gion when English- speaking participants listened to En g-
lish sentences [10]. In contrast, Turkish sentence presen-
tation (control task) did not induce similar cerebral acti-
vations in any of the participants. Reporting similar re-
sults, Mazoyer et al. (1993) used fMRI and PET while
participants were listening to Tamil (participants’ un-
known language) and French (participants’ mother t ong ue)
spoken stories. After subtraction, they found a stronger

Lateralization of Receptive Language Function Using near Infrared Spectroscopy 65
activation for French stories in the left superior and left
medial temporal gyri [5].
Although these studies confirm a left hemisphere spe-
cialization for receptive language processing [5,10], the
specific involvement of different brain regions in each
level of processing is still controversial [11]. Some au-
thors suggest that other processes such as mental imagery
and episodic memory retrieval may be implicated when
subjects listen to stories [12]. For instance, activation that
has been observed in the parieto-temporal junction and in
the prefrontal medial cortex may be due to the latter
processes [11,13]. Because mental imagery and episodic
memory retrieval might be associated with story com-
prehension, their relation with receptive language proc-
essing must be further investigated. To our knowledge,
no previous studies have investigated the impact of epi-
sodic memory and mental imagery processes on the br ain
activation patterns observed in receptive language proc-
essing. The use of a paradigm involving the presentation
of a known story versus an unknown one might shed
light on this matter.
The brain activation patterns of receptive language
processing have been mainly studied with fMRI and PET.
However, the invasive and restrictive nature of these
techniques often make them inappropriate for young
children, epileptic patients or patients with mental retar-
dation [2,14]. To date, few studies have been conducted
with near-infrared spectroscopy, a non-invasive tech-
nique that allows the measurement of blood oxygenation
changes related to cerebral activation [15,16]. Also
known as optical imaging, this technique is based on the
light absorption properties of oxyhemoglobin (HbO) and
deoxyhemoglobin (HbR) [17]. Good agreements have
been observed between NIRS and fMRI, MEG and PET
[9,18,19] However, NIRS has a better temporal resolu-
tion than fMRI and its mobile and cheaper nature confers
it with important advantages over the other techniques.
Moreover, its configuration does not require subject con-
tainment, thus allowing the participant to move and
speak. This makes it ideal while evalu ating cognitive and
linguistic functions or for research with young children
and special populations [2,4,9,20].
The present study aims to investigate the use of NIRS
to assess brain lateralization patterns for receptive lan-
guage functions in healthy adults while further control-
ling for episodic memory retrieval and mental imagery
processes. Using a story listening task, we hypothesized
that 1) French-speaking participants would show a
greater left lateralized activation pattern in response to a
French story compared to an Arabic one and, 2) if epi-
sodic memory retrieval affects the processing of the in-
formation, a different activation pattern should be ob-
served in response to an unknown story (Martine and the
Witch) compared to a known story (Snow White).
2. Methodology
2.1. Participants
Six healthy volunteers (3 men; mean age = 22 years
(16-28 years), SD = 3.85) without neurological impair-
ments were tested. The handedness of each subject was
assessed using the Edinburgh Inventory [21]: four were
right-handed and two were ambidextrous with a right
predominance. All were native from the Quebec province,
French-speaking and without knowledge of the Arabic
language. Two subjects (1 man, 1 woman) were with-
drawn from the analyses due to technical artifacts. This
study has been approved by the Ethics Committee of the
Ste-Justine University Hospital Center and informed
consent was obtained from all participants.
2.2. Optical Imaging Recording
The data were gathered using a multi-channel spec-
trometer Imagent Tissue Oxymeter (ISS Inc., Champaign,
III, USA) made of 50 sources emitting a 690 nm wave-
length, 50 sources emitting a 830 nm wavelength and 16
detectors. The sources were placed on the subject’s scalp
using a rigid helmet adapted to the subject’s head. Due to
the anatomical variability of the subjects’ head, two dif-
ferent helmet sizes were used (57 cm and 59 cm), and a
standard montage was created for each of these helmets.
Both montages were created using the software Brain-
sight TM Frameless 39 (Rogue Research, Can ada) from a
standardized MRI template, the Colin27 [22]. A total of
144 channels, using a source-detector distance from 2.9
cm to 6 cm, were symmetrically laid out to cover the left
cerebral regions known to be related to language func-
tions (Broca’s area and Wernicke’s area), as well as the
right homologous regions. Figure 1 shows the regions
covered by the montage.
For each subject, the exact localization of each source
and detector, as well as four fiducial points (nasion, left
and right pre-auricular, and tip of the nose), were digi-
tized and recorded using the stereotaxic system Brain-
sight to allow the individual reconstitution of the mon-
tage on the MRI template. Finally, a simultaneous EEG
recording with four electrodes placed on the scalp (Fz,
Cz, Pz and Oz according to the 10/20 international sys-
tem) was carried out in order to control for the subjects'
alert state during the task.
2.3. Stimuli
Two stories were used: Snow-White (known story) and
Martine and the Witch (unknown story). Stories were
recorded using Cool Edict ProTm in French and Arabic
by the same speaker to control for acoustic and voice
factors. The amplitude (between 64 dB and 76 dB) and the
duration of the stimuli (20 s each) were adjusted and stan-

Lateralization of Receptive Language Function Using near Infrared Spectroscopy 66
(a)
(b)
Figure 1. Cerebral regions covered by the standard mon-
tage (a) and cortical representation of the activated regions
observed in all subjects (b).
dardized with the sa me software. All the stimuli were pre-
sented to the participants using MatLab 7.0.4 and trans-
mitted by two loudspeakers located at an equal distance
(approximately 155 cm ) from the subject, at ear level.
2.4. Procedure
Testing took place in a dark, sound-proof room. Subjects
came twice to the laboratory. The experimental procedure
and the language sequence were the same from one visit to
the other. Participants were seated, with eyes closed. They
were asked to relax in order to avoid abrupt movements
and to listen carefully to th e stories. They listened first to
the story of Snow-White in both languages and, in a
second testing session, to the story of Martine and the
Witch in both languages. The time interval between both
sessions was approximately two months to control for
repeated measure reactivity. At each visit, participants
listened to short extracts of the story read in French and
the same story extracts read in Arabic. Each condition
comprised 18 blocks with an in terstimulus interval of 4 0s.
Stories were presented in a continuous order to make it
possible for the participant to follow the story. The order
of the language was counter-balanced from one subject
to the other (all the stimuli in French followed by all the
stimuli in Arabic or all the stimuli in Arabic followed by
all the stimuli in French). The total duration of each re-
cording session was approximately 80 min, including the
set-up of the helmet, optodes, detectors and electrodes. At
the end of each session, participants had to answer some
questions related to the stories to further control for com-
prehen sion and attention levels as well as for the familiar-
ity of the stories.
2.5. Data Processing
The data acquisition rate was 19.5312 Hz downsampled
by a factor of 5 to lighten the data processing. The raw
hemodynamic signal was normalized with a 10 s pre-
stimulus time. Artefact rejection took place by with-
drawing segments with light intensity amplitudes smaller
than 100 DC or a normalized standard deviation higher
than 50%. The optical inten sity of the raw data (DC) was
filtered using a low frequency zero-phase digital filtering
with a cut off frequency at 0.1 Hz. A Modified Beer
Lambert Law with a differential path length factor (DPF)
correction according to the age of each subject was ap-
plied [23,24]. Finally, the variation in the HbO and HbR
concentrations were averaged for each channel and each
condition. Averages were co-registered and projected on
the Colin27 standard MRI template [22] to visualize the
activated brain regions. Subsequent analysis was con-
ducted only on the HbO signal.
3. Results
Preliminary analysis—All participants answered correctly
the questions regarding the content of each of the two
stories. None reported having ever heard the “un-known”
story Martine and the Witch and all of them were quite
familiar with the “known” story Snow White. Finally,
EEG monitoring revealed no signs of drowsiness in any
condition.
Using the international 10-20 system [25], six regions
were delimited for all subjects: left frontal-temporal (F7 and
T3), left medial-temporal (T3 and T5) left temporal-parietal
(T5 and P3), as well as the right homologous areas (see
Figure 1(a)). For each of these regions, oxyhemoglobin
(HbO) and deoxyhemoglobin (HbR) changes during task
periods were examined and the region of interest (ROI) was
selected using the maximal amplitude and duration of HbO
changes. Each subject’s ROIs were then fitted on a seg-
mented Atlas 116 template [26].
In response to French, the regions of activation found
in all subjects included the superior temporal gyrus, the
middle temporal gyrus and the angular gyrus (see Figure
1(b) for a representation of the activated areas). Subse-
quent analyses were conducted on these individual ROIs.
Figures 2 and 3 show the hemodynamic changes re-
corded in response to the known and the unknown stories
respectively in both languages for subject GT whose re-
sults are representative of the group. For the French condi-
tion, HbO concentration increased at the beginning of the
story segment in the left hemisphere (blue lines), while in
the right hemisphere only a small increase was observed
(red lines). A maximal peak was recorded around 6 s after
the beginning of the stimulus in both hemispheres and for
both stories. However, the ampli tude of th e cha nge i n th e

Lateralization of Receptive Language Function Using near Infrared Spectroscopy 67
signal induced by the story in French was higher and
lasted longer in the left hemisphere (until 16 s after the
beginning of the stimulus compared to 10 s in the right
hemisphere). This effect was observed for both stories
(known and unknown stories). In contrast, the change in
the hemodynamic signal recorded in response to the story
in Arabic showed a decrease starting at 9 s after the be-
ginning of the stimulus in both hemispheres and for both
stories.
In order to assess the hemispheric lateralization pattern,
a comparison by subtraction was performed. For each of
the four conditions, the hemodynamic signal induced in
the right hemisphere was subtracted from the hemody-
namic signal observed in the left hemisphere. The area
under the curve (AUC) of the subtraction for HbO con-
centration (between 0 and 25 seconds) was then used as a
measure of lateralization. According to this calculation, a
positive HbO AUC would suggest left hemisphere domi-
nance while a negative HbO AUC would suggest right
hemisphere dominance. Figures 2(e), 2(f) and 3(e), 3(f)
display the results of the subtraction for subject GT. The
group mean (four subjects) and standard error of AUC for
each condition are plotted in Figure 4.
Effects of language and story familiarity were further
assessed using a two-way repeated measure ANOVA
(French/Arabic language for known/unknown story), in
which the dependent measure was the AUC resulting
from the subtraction (left AUC minus right AUC). As
expected, results revealed a significant main effect for
language [F (1, 3) = 10.33, p < 0.05] with a large effect
size (eta square = 0.78). The story familiarity (known vs.
unknown) was not significant [F (1, 3) = 0.12, p = 0.75,
eta square = 0.04] neither was the interaction language by
familiarity effect [F (1, 3) = 0.51, p = 0.84, eta square =
0.02].
4. Discussion
Our findings indicate that the hemodynamic signal cha ng es
associated to French stories are greater in the left than the
right temporal regions, suggesting a left hemisphere domi-
nance for receptive language in French-speaking partici-
pants. In contrast, Arabic stories (i.e. unknown language)
did not induce specific hemispheric patterns. Consistent
with previous reports [5,10] using similar listening tasks
in fMRI or PET, the left superior temporal gyrus and left
middle temporal gyrus, were particularly activated. De-
spite the limited sample size of our study, a very large
effect size for language was found, fu rther suppo rting the
efficacy of optical imaging in assessing receptive language
lateralization processes.
Figure 2. Hemodynamic responses to the known story for subject GT. The y-axis indicates relative changes in concentration (mi-
cromolar) for HbO (continuous line) and HbR (dotted line) during presentation of the story segments (20 s). Hemodynamic
changes during stories in French in the left and right hemispheres are represented respectively in (a) and (c), whereas hemody-
namic changes during stories in Arabic in the left and right hemispheres are represented in (b) and (d). Hemispheric subtractions
of the hemodynamic signal (left minus right) are illustrated for the story told in French (e) and in Arabic (f).

Lateralization of Receptive Language Function Using near Infrared Spectroscopy 68
Figure 3. Hemodynamic responses to the unknown story for the same participant (GT). The y-axis indicates relative changes in
concentration (micromolar) for HbO (continuous line) and HbR (dotted line) during the presentation of the story segments (20 s).
Hemodynamic changes during the story in French in the left and right hemispheres are represented respectively in (a) and (c),
whereas hemodynamic chan ges during th e story in Arabic in the left and righ t hemisphere are represented in (b) and (d).
The findings of the present study also provide a new ap-
proach to calculate language hemispheric lateralization.
Previous studies have mainly used the Laterality Index (LI)
formula (L + R/L –R) where L is the maximal peak found in
the left hemisphere and R is the maximal p eak found in the
right hemisphere. The usual LI value goes from –1 (right
hemisphere dominance) to +1 (left hemisphere dominance).
However, the interpretation of the laterality index depends
on the use of subjectiv e parameters such as number o f vox-
els used in fMRI, the maximal peak, or the selected timing
Figure 4. Average (n = 4) of the hemispheric lateralization.
(Area Under the Curve H bO Left - A UC HbO right) in response to the kn own
story (b lack bars) and the unkno wn story (gr ay bars) in bo th languag es. The
y-axis indicates average changes in concentration (micromolar) for HbO
Error bars indicate the standard errors. Positive HbO AUC indicates left
hemisphere specialization while negative HbO AUC suggests right
hemisphere specialization.
[27]. Moreover, its computation is only po ssible with positive
or absolute values, which limits its use with blood-oxygen
level dependent measures (BOLD) as in optical imaging
and fMRI. In the present study, we suggest that subt ract i ng
the hemodynamic signal of the hemispheric regions (Area
under the Curve HBO Left-AUC HBO Right) provides a
more objective measure of hemispheric lateralization. This
new method may be more suitable for optical imaging as it
takes into account the decrease in HbO concentration. The
use of the subtracted AUC values as a measure of la te r al i z a-
tion may thus provide a more confident index because it
better reflects the variation of HbO concentration all along
the story segments. Further validation of this new method
for measuring language late ralization i s needed.
Finally, this study also ai med to determine wheth er the
presentation of a well known story would affect the acti-
vation patterns observed in specific brain regions involved
in memory of imagery processes. Our results suggest that
participants responded similarly to the known and un-
known stories, regardless of the episodic memory re-
trieval expected while listening to the known story. This
result confirms the robustness of our p aradigm in a ss ess in g
language rather than memory processes.
In summary, our findings confirm the use of optical
imaging as a reliable and simple tool to study receptive
language lateralization patterns in adults using story
comprehension paradigms. Taking into account the numer-

Lateralization of Receptive Language Function Using near Infrared Spectroscopy 69
ous advantages of NIRS, these results are encouraging for
further investigation of language development in chi l d re n a s
well as for receptive language lateralization patterns in
special populations such as patients with mental retarda-
tion and/or epileptic patients. This is of special impor-
tance, considering the fact that these populations often
show restricted capabilities making other imaging meth-
ods inappropriate to study language lateralization which,
in cases of intractable epilepsy, constitute a necessary part
of the pre-surgical inv e stigation.
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