Vol.1, No.3, 239-2
doi:10.4236/health.2009.13039
SciRes Copyright © 2009 Openly accessible at http://www.scirp.org/journal/HEALTH/
43 (2009) Health
Right prefrontal cortex is activated for perceiving postural
limits: a functional near-infrared spectroscopy study
Noriyuki Kamata1, Yoshimi Matsuo2, Ayako Matsuya3, Satoru Inoue1, Kazuo Abe3,4
1Rehabilitation Unit, Osaka University Hospital, Osaka, Japan;
2Faculty of Rehabilitation, Kobe Gakuin University, Hyogo, Japan
3Faculty of Nursing and Rehabilitation, Konan Women’s University, Hyogo, Japan
4Department of Neurology and Rehabilitation Center, Konan Hospital, Hyogo, Japan
Received 25 September 2009; revised 26 October 2009; accepted 27 October 2009.
ABSTRACT
The purpose of this study was to investigate
neuronal mechanisms active during the percep-
tion of forward postural limits in a standing po-
sition and to specify fall-related brain activity
using optical functional near-infrared spectros-
copy. The study group included six right-handed,
healthy female volunteers (range: 19, 20 years).
The optical imaging device comprised 16 opto-
des designed to provide 24-channel recording of
changes in hemoglobin oxygenation. We meas-
ured the changes of oxygenated hemoglobin
levels in the frontal region when subjects per-
ceived reachability in a standing position. Com-
pared with those in other regions, the oxygen-
ated hemoglobin levels in the right frontal region
compatible with the right prefrontal cortex sig-
nificantly increased. This result suggests that
brain activities in the right prefrontal cortex are
related to perception of reachability. Overesti-
mation of postural limits has been reported as
one of the risk factor for falling. This overesti-
mation might be induced by dysfunction in the
prefrontal cortex, resulting in a failure to inhibit
a motor program that would have caused a loss
of balance in reaching. Activation of the right
prefrontal cortex may be a key factor for pre-
venting accidental falls in the elderly and in pa-
tients with neurological disorders.
Keywords: Postural Limits; Falls; Functional
Near-Infrared Spectroscopy (fNIRS); Prefrontal
Cortex (PFC)
1. INTRODUCTION
Most people can appropriately perceive reachability, which
is defined as the distance to which one could reach if actually
executing the reach. Previous studies often utilized forward
perceived reachability in a standing position as an index of
one’s own perceived postural limits [1-3]. Reaching move-
ments are programmed based on this perception, and one
can usually execute these movements safely by keeping the
center of mass within postural limits [4].
Our previous study and others have reported that eld-
erly and neurological patients, including patients with
Parkinson’s disease, tended to overestimate their reach-
ability when standing, and thus, overestimate their own
postural limits, even if a target is not within actual reach
[3,5]. In addition, this overestimation has been reported as
one of the risk factors of multiple falls [6]. Therefore,
improving the perception of reachability might decrease
the number of accidental falls in the elderly and in neu-
rological patients. For creating a rationale for this new
intervention, it is useful to investigate the neuronal
mechanisms of this abnormal estimation of reachability.
However, no research has yet examined such brain ac-
tivities with regard to perception of reachability.
Functional near-infrared spectroscopy (fNIRS) can
evaluate cortical activity by measuring the changes of
hemoglobin oxygenation of blood within a few centime-
ters of the skull surface [7]. We adapted this technique to
our study since it was suitable for use during dynamic
tasks such as walking and in a standing position [8,9].
Thus, the purpose of this study was to clarify neuronal
mechanism during the perception of forward postural
limits in a standing position by fNIRS and to specify
fall-related brain regions.
2. METHODS
2.1. Subjects
The study group included six right-handed, healthy fe-
males (range: 19, 20 years). Informed consent was ob-
tained form each subject in accordance with the Helsinki
Declaration.

N. Kamata et al. / HEALTH 1 (2009) 239-243
SciRes Copyright © 2009 Openly accessible at http://www.scirp.org/journal/HEALTH/
240
analog switch
in left hand
optodes of fNIRStarget of functional reach instrument
70cm
analog switch
in left hand
optodes of fNIRStarget of functional reach instrument
70cm
Figure 1. Position of subject and experimental devices. The
target of the functional reach instrument can be moved along the
dotted line. The distance from the target to the subject is 70cm.
9
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(b)(a)
Figure 2. (a) Schema for location of the array of optodes. The
optode array consists of 8 light fibers (white circles) and 8
detectors (black circles). The change of dortical hemoglobin
content was measured in each channel between a light fiber and
a detector (square numbers from 1 to 24). The center of the 4th
row of optodes (channel 2) was located in the Cz position of the
international 10-20 system. (b) Location of 13 regions of interest
(circles labeled A-M). Each region consists of 4 near-
est-neighbor channels For example, region of interest A was
formed by channels 1, 4, 5, and 8.
１task (35s)
Pre
(10s)
PR
task
(15s) Post
(10s)
Pre
(10s)
Control
task
(15s) Post
(10s)
Total 350s
１task (35s)
Pre
(10s)
PR
task
(15s) Post
(10s)
Pre
(10s)
Control
task
(15s) Post
(10s)
Total 350s
Figure 3. Task design for fNIRS. The perceived reachability tasks
(taller blocks) and control tasks (lower blocks) were measured
alternately and repeated continuously 5 times.
2.2. Experimental Devices
We used an optical imaging device (FOIRE3000, Shi-
madzu, Kyoto, Japan) and a standard device for the
functional reach test [10] (GB-200, OG Giken, Okayama,
Japan) with a wired analog switch. Subjects stood before
the target of the functional reach test instrument with
their feet positioned shoulder-width apart, holding the
analog switch in their left hand (Figure 1).
2.3. fNIRS
The schema for location of the array of optodes in opti-
cal imaging device is showed in Figure 2a. The device
consisted of 16 optodes, including 8 light-source fibers
and 8 detectors arranged in a 4 × 4 array with the inter-
optode distance set at 3.0cm. We located the center of
the 4th row of optodes in the Cz position, in accordance
with to the international electroencephalogram 10-20
system. This configuration permitted 24-channel re-
cording of changes in oxygenated hemoglobin (oxy-Hb),
deoxygenated hemoglobin (deoxy-Hb), and total hemo-
globin (total-Hb) in the motor-related cortex within the
covered 9×9-cm skull surface.
2.4. Task Design and Experimental Protocol
The task design for this fNIRS study is shown in Figure 3.
We conducted two tasks, the perceived reachability task
and the control task. Each task took a total of 35 seconds
and consisted of a 10-second pretask period, a 15-second
task period, and a 15-second posttask period. The two
tasks were measured alternately, and the protocol was
repeated 5 times. Total duration for each fNIRS measure-
ment session was 350 seconds.
During the tasks, the subject was instructed to concen-
trate on the target while in a standing position with arms at
her sides and maintaining a static posture. In the perceived
reachability task, the examiner moved the target in a direc-
tion away from the subject during the 15-second test. When
the subject judged that the target had arrived at the reach-
able limit for her right arm, she pushed the analog switch to
record her perception. In control tasks, the examiner moved
the target in a direction nearer to the subject.
2.5. Data Analysis
The hemoglobin oxygenation data was sampled every
160ms. We used the change of oxy-Hb level (mM-cm) as
the index of cortical activity. When cortical activity in-
creased, cortex needed more oxygen that increases oxy-
Hb level and it correlated better with the change of re-
gional cerebral blood flow than deoxy-Hb or total-Hb
[11]. First, the 5 repetitions of oxy-Hb measurement in
each task were grand-averaged in each channel. In addi-
tion, we obtained the data from the last 10 seconds of
each task period because hemodynamic changes as
measured by fNIRS lag behind the task stimulus by a
few seconds [12]. Second, to adjust for the influence of

N. Kamata et al. / HEALTH 1 (2009) 239-243
SciRes Copyright © 2009 Openly accessible at http://www.scirp.org/journal/HEALTH/
241
＊
２４ ２３
２１
２２
２０ １８１９
１６１７ １５
１４ １３ １１１２
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８
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３
１０ ９
２ １
M
C
HG
I
F
L
E
J
K
RtLt
B
D
A
-2.1
-1.6
-1.1
-0.6
-0.1
0.4
0.9
1.4
1.9
2.4
ABCDEFGHI JKLM
oxy-Hb
deoxy-Hb
total-Hb
*
*
***
*P<0.05
**
*
＊
２４ ２３
２１
２２
２０ １８１９
１６１７ １５
１４ １３ １１１２
７５
８
６４
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２ １
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C
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I
F
L
E
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B
D
A
＊
２４ ２３
２１
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２０ １８１９
１６１７ １５
１４ １３ １１１２
７５
８
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１０ ９
２ １
２４ ２３
２１
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１６１７ １５
１４ １３ １１１２
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-2.1
-1.6
-1.1
-0.6
-0.1
0.4
0.9
1.4
1.9
2.4
ABCDEFGHI JKLM
oxy-Hb
deoxy-Hb
total-Hb
*
*
***
*P<0.05
**
*
(a) (b)
Figure 4. Mean values of effect size in regions of interest. (a) Values are mean ± standard error. Effect size of oxy-Hb (white bars) or
total-Hb (hatched bars) significantly increased in regions A, B, D, F, and K. The effect magnitude of deoxy-Hb (black bars) tended to
show negative scores. (b) The effect size of oxy-Hb located in regions of interest A, B, D, F, and K significantly increased (black circles).
differential light-path lengths among subjects or chan-
nels and to emphasize the changes of oxy-Hb level dur-
ing perception of reachability, the effect size was calcu-
lated by the following formula: Effect size = (mean
oxy-Hb during perceived reachability task – mean
oxy-Hb during control task) / standard deviation of
oxy-Hb during the control task [8,13]. Finally, we estab-
lished 13 regions of interest, which consisted of the 4
nearest neighboring channels (Figure 2b). The data for
each region included a total of 24 effect-size values (6
subjects × 4 channels). On the basis of these values, we
used 1-sample t tests to assess the regions in which the
oxy-Hb level was significantly increased during the per-
ception of reachability. Statistical significance was de-
fined as P<0.05.
To examine changes of oxy-Hb, deoxy-Hb and to-
tal-Hb during control task, we calculated the Z scores in
each subject and each channel by following fomula: Z
score = (mean value during control task – mean value
during pretask period of control task) / standard devia-
tion during pretask period of control task [12]. All mean-
Z scores of oxy-Hb, deoxy-Hb and total-Hb in each
channel ranged from -1 to 2 and therefore, we judged
that hemoglobin levels were not changed by the control
task.
3. RESULTS
The mean values of effect size in each channel are
shown in Table 1. The effect tended to increase in the
right frontal region during the perception of reachability.
Statistical analysis also showed that the mean oxy-Hb
effect size significantly increased in regions of interest A,
B, D, F, and K (P<0.05) (Figure 4).
4. DISCUSSION
The significant change in oxy-Hb during the perception
of reachability indicated increased neural activity in the
right frontal lobe. Previous researches have reported that
the perception of reachability was estimated by internal
mental simulation or motor imagery of the reaching
movement [14-16]. Literally, motor imagery for the right
hand recruits multiple cortical areas, including the left
supplementary motor area, the premotor cortex [17], and
the primary motor cortex [18]. As previous studies have
indicated that motor imagery is related to estimation of
the right arm-reach range, neural activity would be pre-
dominantly in the left frontal lobe, not in the right frontal
lobe. However, since we observed activations in the right
frontal lobe, our results do not support the existence of a
close connection between perceived reachability and
motor imagery. The lateral area of Cz position in the
international 10-20 system corresponds with sensorimo-
tor cortex. Significant increases of oxy-Hb level in re-
gions of interest A, B, and D may be induced by the act
of pushing the analog switch in the left hand during the
perceived reachability task. Thus, we hypothesize that
regions F and K in the right frontal lobe, located in the
prefrontal cortex (PFC), are key regions in the percep-

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242
Table 1. The mean effect size of oxy-Hb, deoxy-Hb and total-Hb in each Channel.
Ch11.11± 1.68-0.34± 0.690.78± 0.78
Ch20.45± 1.300.12± 0.220.52± 0.50
Ch30.42± 1.730.06± 0.810.75± 0.68
Ch40.43± 1.21-0.16± 0.560.51± 0.51
Ch50.79± 1.370.12± 0.520.70± 0.54
Ch60.80± 1.800.23± 0.620.86± 0.68
Ch7-0.40± 0.720.19± 0.600.28± 0.42
Ch80.53± 1.05-0.20± 0.580.49± 0.47
Ch90.87± 2.500.26± 0.631.07± 0.94
Ch100.07± 1.01-0.09± 0.520.38± 0.43
Ch110.62± 1.400.06± 0.850.73± 0.57
Ch120.90± 1.40-0.52± 0.640.60± 0.70
Ch130.34± 1.71-0.07± 0.840.70± 0.69
Ch14-0.08± 1.560.40± 0.890.69± 0.65
Ch151.22± 2.31-0.27± 1.191.11± 1.00
Ch160.17± 1.20-0.55± 1.150.49± 0.70
Ch170.74± 2.34-0.45± 0.980.90± 1.00
Ch182.55± 3.43-3.22± 4.841.90± 2.91
Ch190.39± 3.050.08± 1.251.19± 1.20
Ch200.62± 3.95-1.06± 2.641.54± 1.88
Ch210.25± 1.89-0.31± 1.070.73± 0.83
Ch221.47± 3.11-2.76± 1.890.93± 2.04
Ch230.89± 3.03-0.92± 2.561.39± 1.56
Ch240.41± 2.61-0.89± 3.001.28± 1.58
Effect size of oxy-HbEffect size of deoxy-HbEffect size of total-Hb
Values are mean ± standerd diviation.
tion of reachability in a standing position; in other words,
perception of the subject’s own postural limits.
We also investigated the functional relationship be-
tween perceived reachability and cognitive function.
Previous studies have shown that healthy young subjects
tend to overestimate their own reachability while in a
sitting position, although they underestimate their own
reachability in a standing position. Robinovich [2] called
this underestimation a potential safety factor in reducing
the risk of loss of balance. This safety factor means that
the process of perceiving one’s own postural limits are
controlled by an inhibitory neural mechanism of a motor
program executing the reaching motion without risk of a
fall. Shallice proposed the notion of a supervisory atten-
tional system in the frontal lobe that selects appropriate
schema among activated schemas in response to various
situations, subsequently inhibiting inappropriate ones
[19]. In addition, the PFC in the right hemisphere is ac-
tivated by a GO/NO-GO task [20]. Therefore, the right
PFC activity observed in our study may represent an
inhibitory mechanism for estimating safe reaching in a
standing position. Recently, Ambrose et al. reported that
elderly fallers with impaired working memory overesti-
mated their postural limits compared with those with
preserved working memory [21]. They also reported that
an impaired executive function might promote fall risks
due to misjudgment of motor planning in daily activity.
Working memory and executive function are believed to
be conducted mainly in the PFC [22]. Consequently, our
results indicate that working memory may be associated
with perception of one’s own postural limits.
5. CONCLUSIONS
Overestimation of postural limits is a possible risk factor
for falls. Our study using fNIRS suggests that overesti-
mation of the postural limits may result from dysfunction
of the right PFC, which subsequently fails to inhibit an
inappropriate motor program. Thus, activation of the right
PFC may be a key factor for preventing accidental falls in
the elderly and in patients with neurological disorders.
Interventions to activate the right PFC could be useful for
preventing accidental falls.
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