Ohsugi et al. BMC Neuroscience 2013, 14:10
http://www.biomedcentral.com/1471-2202/14/10

RESEARCH ARTICLE

Open Access

Differences in dual-task performance andprefrontal cortex activation between younger andolder adults
Hironori Ohsugi1*, Shohei Ohgi1†, Kenta Shigemori2† and Eric B Schneider3†

Abstract
Background: The purpose of this study was to examine task-related changes in prefrontal cortex (PFC) activity
during a dual-task in both healthy young and older adults and compare patterns of activation between the agegroups. We also sought to determine whether brain activation during a dual-task relates to executive/attentional
function and how measured factors associated with both of these functions vary between older and younger
adults.
Results: Thirty-five healthy volunteers (20 young and 15 elderly) participated in this study. Near-infrared
spectroscopy (NIRS) was employed to measure PFC activation during a single-task (performing calculations or
stepping) and dual-task (performing both single-tasks at once). Cognitive function was assessed in the older
patients with the Trail-making test part B (TMT-B). Major outcomes were task performance, brain activation duringtask (oxygenated haemoglobin: Oxy-Hb) measured by NIRS, and TMT-B score. Mixed ANOVAs were used tocompare task factors and age groups in task performance. Mixed ANOVAs also compared task factors, age groupand time factors in task-induced changes in measured Oxy-Hb. Among the older participants, correlations between
the TMT-B score and Oxy-Hb values measured in each single-task and in the dual-task were examined using a
Pearson correlation coefficient.
Oxy-Hb values were significantly increased in both the calculation task and the dual-task within patients in bothage groups. However, the Oxy-Hb values associated with there were higher in the older group during the post-task
period for the dual-task. Also, there were significant negative correlations between both task-performance accuracy
and Oxy-Hb values during the dual-task and participant TMT-B scores.
Conclusions: Older adults demonstrated age-specific PFC activation in response to dual-task challenge. There wasalso a significant negative correlation between PFC activation during dual-task and executive/attentional function.
These findings suggest that the high cognitive load induced by dual-task activity generates increased PFC activity
in older adults. However, this relationship appeared to be strongest in participants with better baseline attention
and executive functions.
Keywords: Dual-task, Near-infrared spectroscopy, Executive function, Attentional function* Correspondence: hironori.o.10.30@gmail.com†
Equal contributors
1
Graduate School of Health Sciences, Seirei Christopher University, 3453
Mikatahara-Cho, Hamamatsu-City, Shizuoka 433-8558, Japan
Full list of author information is available at the end of the article© 2013 Ohsugi et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andreproduction in any medium, provided the original work is properly cited.

Ohsugi et al. BMC Neuroscience 2013, 14:10
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Background
Cognitive functions, such as selective attention, memory
and executive function, decline with age [1,2]. The population is aging with ever larger numbers of individuals
reaching ages where decline in function is more common [3]. Age-related changes to the brain have beenshown to occur earliest in the prefrontal cortex (PFC)[4]. The PFC has been associated with memory, attention,
executive function and emotion, as well as playing a rolein a variety of other complex cognitive functions [5-7].
Pathological or age-related changes in this area have been
associated with a number of neuropsychiatric disorders
with cognitive, emotional, behavioral, or affective manifestations. These disorders include schizophrenia, depression
and dementia [8]. The decline in cognitive ability associated with aging has been related to disuse of certain
cognitive functions and a corresponding reduction inbrain activity [9]. Previous studies have suggested that
increasing activity in the PFC might be able to prevent, ormoderate, age-related changes to the brain [10]. Neuronal
activation leads to increase of regional cerebral blood flow
[11,12]. In addition to increased blood flow in active areas,other factors associated with the transport of certain
blood-borne factors have been shown to be increased inbrain areas in the presence of increased neural activity.
For example, Nishijima, et al. [13] showed that neuronal
activity elicited by electrical, sensory, or behavioral stimulation increases insulin-like growth factor-1 (IGF-I) input
in activated regions. IGF-1 modulates neuronal growth,survival, neural excitability, and cognitive function. Therefore, it might be hypothesized that regular activation of
the PFC may prevent decline of the brain functions associated with this most important brain area.
Numerous studies have reported that regular physicalactivity and cognitive training are associated with better
cognitive function [14-18]. Therefore, it is thought that a
combination of both cognitive and physical activity
might be useful in preventing, or slowing, the decline ofcognitive function seen in many older adults. There is
growing evidence that dual-task (combining both physicaland cognitive activity) training better supports healthy
executive function, working memory and the ability to
divide attention than either physical or cognitive training
in isolation [19-23]. Current literature suggests that dualtask activity also may be an effective tool to prevent the
decline of overall cognitive function [24-26]. Pedroso et al.
[24] showed that, over time, dual-task training improves
dual-task performance in patients with mild to moderatedementia. Erickson et al. [26] showed that improvementsof dual-task performance correlate with measured changes
in brain activation. Also several neuroimaging studies haverevealed increased brain activity in the PFC during dualtask activity. D’Esposito et al. [27] compared single-task
performance with a concurrent performance of both tasks

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and discovered that activation of the PFC occurred only
during the dual-task condition whereas this area was not
active during either single-task. Koechlin et al. [28] also
demonstrated increased activation in PFC bilaterally
during a dual-task condition compared to similar measurements when a single-task was being performed. However, Callicott et al. [29] have demonstrated an ‘inverted-U’
shaped neuro-physiological response as subjects are moved
from activities producing the lowest cognitive load
toward those producing the highest cognitive load leading these authors to suggest that excessive processing
demands are actually accompanied by a diminution incortical activity. In another study, Reuter-Lorenz andCappell [30] suggested older adult demonstrated overactivation in PFC during a cognitive task.
A number of studies have suggested that older age isassociated with substantial differences in hemodynamic
response to stimuli. For example, Schroeter [31] suggested that aging decreases the hemodynamic responsein the frontal association cortex during cognitive task. In
this way, the brain activation during dual-task in older
adults was still controversial. Therefore, the purposes ofthis study were as follows: 1) to clarify and compare
task-related changes in PFC activity, measured by examining changes in brain blood oxygen levels comparing brain
activation during single-task activities with a dual-task; 2)
to examine age-related differences across single- and dualtask conditions between healthy young individuals andhealthy older adults; 3) to examine whether levels of brain
activation during dual-task activity are associated withbaseline levels of executive and attentional functioning in
the older age group.

Methods
Participants

Thirty-five healthy volunteers participated in this study.
The younger group was selected from individuals aged
21–35 years of age and included 20 individuals. The
older group was selected from individuals greater than
65 years of age and included 15 individuals. All participants
were healthy and without impairment of visual or auditory
senses. Both young and old participants demonstrated independence in activities of daily living. Informed consent
was obtained from all participants prior to enrollment.
Written informed consent was obtained from the patient
for publication of the image in Figure 1. A copy of the written consent is available for review by the Editor-in-Chief of
this journal. This study was approved by the Ethics
Committee of Seirei Christopher University (approvalNo. 10054).
ProtocolThe independent motor execution task (physical singletask) was performed by seated participants stepping inOhsugi et al. BMC Neuroscience 2013, 14:10
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Figure 1 NIRS probe setting and task protocol. On the left: NIRS probe setting, on the right: brain mapping and ROI setup, bottom: task
protocol.

place with each foot while counting out loud forwardfrom zero. The cognitive single-task involved serial
subtractions of 7 beginning with 100 and continuing asfollows: 100, 93, 86, 79, etc. The results of each calculation were spoken out loud so accuracy could beassessed. Both the physical and cognitive single-tasks
were performed in the seated position with eyes closed.
The dual-task combined the cognitive and motor execution tasks with seated participants performing anotherseries of serial 7 subtraction problems while stepping,again with their eyes closed. PFC activation wasrecorded using near-infrared spectroscopy (NIRS) during
both the physical and cognitive single-task activities aswell as during the dual-task. Figure 1 demonstrates theexperimental protocol. Each subject was instructed toperform either one of the single-tasks or the dual-task
randomly after a rest period. In order to randomize theorder of tasks across individuals, subjects selected one
task pattern from the six possible patterns by lot (the tasks
and the associated patterns for selection were as follows: 1)
stepping task, 2) calculation task, 3) dual-task, 1-2-3/
1-3-2/ 2-1-3/ 2-3-1/ 3-1-2/ 3-2-1,) (Figure 1). Rest and task
periods were set for 30 seconds and each task was repeatedthree times. During the rest period, participants were asked
to simply count out loud at their own pace.
Measurement of brain activation

PFC activity was assessed using the NIRS (ETG-7100,
Hitachi Medical, Tokyo, Japan) which uses two wavelengths of near-infrared light (695 nm and 830 nm). The
distances between the injectors and detectors were
3.0 cm, and it was determined that the machine measures points associated with the surface of the cerebral

cortices [32,33]. The NIRS probes contain 3 × 10 lines ofplastic transmitter/receiver shells (47 channels). We
placed the optode grid on the head of the subjects
according to 10–20 positions and the lowest probes wereplaced along Fp1-Fp2 (Figure 1). NIRS measured therelative changes in the concentrations of oxygenatedhemoglobin (Oxy-Hb), deoxygenated hemoglobin (DeoxyHb) and total hemoglobin (Total-Hb). Fundamental
data of Hb was display and uses [mM*mm], which isan index of Hb change as a scaled variable. We usedchanges in oxy-Hb values as indicators of change inthe regional cerebral blood volume, because the oxyHb is more sensitive than deoxy-Hb as a parameter formeasuring the blood flow changes associated withbrain activation [34]. Sampling frequency was 10 Hz,
the processed moving average was 5 seconds, a 0.5 Hz
low-pass filter was used to remove the effects of Mayer
waves and a 0.01 Hz high-pass filter was used to remove baseline drift. Baseline corrections were madeusing the least squares method based upon the value ofthe measurement 10 seconds before task initiation andthe value of the measurement 20–30 seconds after taskcompletion. The task was repeated three times and thedata from each of the three task blocks were averaged.
These analyses were performed using the ‘integral
mode’ of the ETG-7100 software. The Oxy-Hb data
produced by the NIRS probes were segregated by theregion of interest (ROI) [35], and the probes focusedon the PFC were isolated for analysis. 14 channels(probe number 22, 23, 24, 25, 26, 32, 33, 34, 35, 41, 42,
43, 44, 45) corresponded to the PFC and were selected
as the ROI (Figure 1). Average values for Oxy-Hb were
calculated across the whole task period to confirm theOhsugi et al. BMC Neuroscience 2013, 14:10
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task related change, and at each 10 second period toconsider the time-dependent change, namely, pre-task,
task 0-10s, task 10-20s, task 20-30s, post task 0-10s,
post task 10-20s, post task 20-30s.
Task performance

The number of steps made by each participant during
both the stepping single-task and the combined dual-task
were counted. The total number of serial 7 subtractions
performed were counted and the numbers of correct andincorrect subtractions were recorded during both thesubtraction single-task and the combined subtraction/
stepping dual-task. The proportion of correct subtractions
was calculated for both single and dual-task trials.
Measurement of baseline cognitive function among theolder adults

The Mini-Mental State Examination (MMSE) and TrailMaking Test (TMT) were performed for assessment ofcognitive function in older participants. MMSE is one of
the most common tools to screen for cognitive impairment
in older adults [36]. The MMSE screens for impairment inoverall brain function (i.e. the frontal, parietal, and temporal lobes) [37]. The TMT assesses several cognitive
functions including working memory, attention, motor
speed and more [38,39]. The TMT consists of twoparts, A and B. Performance on TMT Part B (TMT-B)
has been associated with PFC-related cognitive functions,
including executive function, attention and working
memory [39,40]. Because we were specifically examining
PFC activity and function and wanted to determine if
there was a relationship between baseline cognitive functioning and PFC activity in the older adult group, TMT-B
was administered to the older participants. TMT-B
consists of numbers from 1 to 13 and Japanese charactersscattered on a sheet of paper, and participants must draw
a line alternately between consecutive numbers and theappropriate sequential Japanese character. The timerequired to complete the TMT-B task was measured foreach participant and was collected as required, accounting for the number of errors present. The number of
errors in TMT has been associated with attentional
control, working memory and executive functioning[41]. Errors involve drawing a line between a particularcharacter or number and an inappropriate number, or
failing to draw a line between characters in accordancewith the instructions.
Statistical analysis

To compare task factors and age groups in task performance (number of steps, total number answered, proportionof calculations performed correctly), we performed mixed
ANOVAs respectively with group (younger vs. older) as
the between subjects variable and task (single vs. dual) as

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the within-subjects variable. To compare the Oxy-Hb
values associated with task factors and age groups, we
performed mixed ANOVA with age group (younger vs.
older) as the between subjects variable and task (steppingvs. calculate vs. dual) as the within-subjects variable. To
compare task factor, age group and time factor in taskinduced changes in Oxy-Hb values at various times acrossthe study period using the longitudinally collected NIRS
data, we performed mixed ANOVA with group (younger
vs. older) as the between subjects variable and, task
(stepping vs. calculate vs. dual) and time factor (pre-task,
task 0-10s, task 10-20s, task 20-30s, post task 0-10s, post
task 10-20s, post task 20-30s) as the within-subjects
variables. Post hoc tests were performed using the
Bonferroni method to reduce the possibility of Type I
errors [42]. To examine the relationship between cognitive functioning and brain activation, the correlation
between the TMT-B score (number of errors), Oxy-Hb
values in whole task period in each task and dual-task
performance in the older age group was analyzed usinga Pearson correlation coefficient. All statistical analyses were performed using IBM SPSS Statistics 19(SPSS, Inc., an IBM Company, Tokyo, Japan), the levelof statistical significance was set at 0.05.

Results
Background of participants

The younger participants (10 males and 10 females)
ranged in age from 22 to 35 years (mean: 26.0, S.D. 3.6)
and the older participants (6 males and 9 females)
ranged in age from 69 to 87 years (mean: 77.9, S.D. 5.3).
None of the older participants had a score below 25 on
the MMSE (mean MMSE score: 28.9, S.D. 1.5). The
mean time required for the older participants tocomplete the TMT-B was 161.4 seconds (S.D. 105.4) andthe mean number of error in TMT-B was 2.8 (S.D. 2.6).
The MMSE and TMT were not given to the younger
participants.
Task performances

There were main effects of age group on the proportion of calculations performed correctly (F (1, 33) =10.02, P < 0.01, partial η2 = 0.23) and task factor in
number of steps (F (1, 33) = 7.39, P = 0.01, partial η2 = 0.18).
There were no main effects of task factor in proportion
performance correctly (F (1, 33) = 0.04, P = 0.84), in total
number answered (F (1, 33) = 0.04, P = 0.84). Also, no main
effect was shown for age group in total number
answered (F (1, 33) = 0.11, P = 0.74) and in number ofsteps (F (1, 33) = 0.56, P = 0.46). The age group by task
factor interaction was not significant in each parameter(in number of steps (F (1, 33) = 0.28, P = 0.10), in total
number answered (F (1, 33) = 0.00, P = 0.97), in proportion
performance correctly (F (1, 33) = 0.45, P = 0.51)). However,Ohsugi et al. BMC Neuroscience 2013, 14:10
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the post hoc test showed that the number of steps was significantly lower for the dual-task compared with thesingle-task in the older group (P < 0.01). Older participants
performed fewer computations correctly than younger
participants in both the computational single-task (85.4%
vs. 96.3%, respectively, P < 0.01) and the combined dualtask (87.5% vs. 96.0%, respectively, P < 0.01) (See: Table 1).

Table 2 The Oxy-Hb value in whole task period

NIRS results
Table 2 showed the Oxy-Hb value in whole task period.
The Oxy-Hb values across the entire testing period
showed a significant relationship with task performance(F (2, 32) = 23.57, P < 0.01, partial η2 = 0.42), but not
across age groups (F (1, 33) = 14.31, P = 0.26). The agegroup by task factor interaction was not significant ineach parameter (F (2, 32) = 1.26, P = 0.29). Post hoc testing showed Oxy-Hb values during the stepping task
were significantly lower than during the calculation task
(P < 0.01) and the dual-task (P < 0.01). The Oxy-Hb
values in the time series demonstrated a main effect for thetime factor (F (6, 198) = 12.86, P < 0.01, partial η2 = 0.28). Theinteractions were significant between time factor and age
group (F (6, 198) = 3.29, P < 0.01, partial η2 = 0.09) andtime factor by task factor (F (12, 396) = 8.91, P < 0.01,
partial η2 = 0.21). Examined across the study interval,
Oxy-Hb values during the dual-task showed a significant time factor by age factor interaction (F (6, 198) =4.31, P < 0.01, partial η2 = 0.21). Post-hoc test results
showed that the older group demonstrated higher OxyHb values than the younger group (P < 0.01) within the
post-task 0-10s period for the dual-task activity. There
were no significant time factors by age factor interactions in either the calculation (F (6, 198) = 1.00, P = 0.42)
or the stepping single-task activities (F (6, 198) = 1.09,
P = 0.37) (See: Figure 2 and 3).

errors in TMT-B was also negatively correlated with thepercentage of correct calculations during the dual-task(r = −0.58, P < 0.05). The Oxy-Hb values observed during the calculation task, as well as during the step task,
were not significantly correlated with TMT-B scores(calculation task: r = −0.46, P = 0.09, stepping task:r = −0.29, P = 0.30) (See: Figure 4).

Correlation between dual-task performance, Oxy-Hb
values and the TMT-B in the older group

There was a significant negative correlation between the
Oxy-Hb values during the dual-task and the number of
errors in TMT-B (r = −0.63, P < 0.05). The number ofDual-task

Younger group

Older group0.024 ± 0.056

0.049 ± 0.045

Calculation task

0.036 ± 0.047

0.037 ± 0.030

Stepping task

−0.015 ± 0.038−0.015 ± 0.015

mean ± S.D.

Discussion
We examined PFC activation by measuring changes in
the concentration of Oxy-Hb levels in the PFC using
NIRS during a dual-task condition and compared thiswith measured activation during two different singletasks (calculation and stepping). The results demonstrated that: 1) Oxy-Hb values were significantly
increased during both the calculation single-task and the
combined dual-task; 2) during the dual-task, the older
adults demonstrated significantly higher Oxy-Hb values
than the younger adults, and 3) the increased activation(higher Oxy-Hb values) associated with dual-task performance in the older participants persisted 10 seconds
beyond the completion of the task itself. Also, there wasa significant negative correlation between Oxy-Hb values
during the dual-task and TMT-B scores. There was also
a significant negative correlation between the proportionof correct calculations made during the dual-task andTMT-B scores.
Increasing Oxy-Hb values has been demonstrated tobe related to increases in cerebral blood volume inresponse to neuronal activation [12]. Measured Oxy-Hb
was significantly increased during both the dual-task andthe calculation single-task compared to the stepping
single-task. As expected, increased Oxy-Hb was not

Table 1 Task performance
Younger group
Number of steps a
Total number answered b
Proportion performed correctly b

Older group

Single-task

Dual-task

Single-task

Dual-task

40.8 ±9.139.5 ± 9.7

45.5 ± 11.0

40.1 ± 14.0*

8.1

8.3

7.7

8.0

(2.6-19.7)(2.0-19.3)(4.0-20.3)(3.3-24.0)

96.3

96.0

85.4**

87.5**(72.9-100)(71.4-100)(41.7-100)(52.9-100)

a: mean ± S.D., b: Median (range), *: significant different between single-task and dual-task (P < 0.05), **: significant different between younger and older group(P < 0.01).
The number of steps was significantly decreased in dual-task compared with single task in the older group. The proportions performed correctly were significantly
lower in the older group than in the younger group in both tasks.

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Figure 2 Hemodynamic changes in PFC in each task (true timecourses). Top: in dual-task, middle: in calculation task, bottom: instepping task, solid line: Older group, dotted line: Younger group.

observed in the PFC during the stepping single-task because this is a simple motor task which does not require
activation in the PFC. It is possible that the stepping
single-task might increase Oxy-Hb in motor-relatedareas of the brain. However, this was not measured during our study. Both the calculation single-task and the
combined dual-task require PCF activation and our findings support the results reported in previous studies[21,22,43,44]. It has been suggested that actively increasing PFC activation in aging individuals might help
to prevent or delay age-related changes to the brain[10,13]. Therefore, a regular schedule of dual-task
training for older individuals might mitigate the age-

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Figure 3 Hemodynamic changes in PFC in each task (averaged
in 10 sec). Top: in dual-task, middle: in calculation task, bottom: instepping task, solid line: Older group, dotted line: Younger group.

related decline of cognitive function often observed inolder adults.
Time series measurements of Oxy-Hb values in boththe stepping and calculating single-tasks demonstrated
no significant difference between younger and older participants. This suggests that PFC activities in response toeither single-task did not differ across age groups. However, significantly different temporal patterns of Oxy-Hb
values were observed between the two age groups when
performing the combined dual-task. In the older group,
Oxy-Hb levels gradually increased and this increase wassustained until the completion of the dual-task. Among
younger participants, Oxy-Hb levels increased rapidly at

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Figure 4 Correlation between Oxy-Hb values and the TMT-B in
the older group. (○): dual-task, (●): calculation task, (□): steppingtask.

the onset of the dual-task and decreased substantiallyprior to task completion. Reuter-Lorenz and Cappell[30] have demonstrated overactivation in lateral and inferior PFC during higher levels of task demand in older
individuals. Our results support previous reports that
dual-task activity is associated with increased brain activation due to higher cognitive load in older participants.
The results of this study, which indicated that older participants had higher PFC activation during the dual-task
period, correspond with those reported by ReuterLorenz and Cappell [30] and suggest that performing adual-task might impose a higher cognitive load in theolder individuals compared with the younger participants. During dual-task performance, the number ofsteps counted by older participants was significantly
decreased compared to the number of steps counted
during performance of the stepping single-task. However, among older subjects, neither the number of calculations, nor the proportion performed correctly differedsignificantly during the dual-task from those observed
during single-task performance. From our observations
during the dual-task, it appears that older participants
may turn their attention to the execution of the calculation task at the expense of the stepping task while young
subjects are able to maintain appropriate attention to both
calculation and stepping. This finding suggests thatolder participants required increased PFC activation inorder to maintain attention to both the stepping andcalculating tasks. It is possible that this requirement
for increased PFC activation is related to decreased
brain function associated with aging.
The comparison of single-task performance between
young and older participant demonstrated a significant
different in the proportion of calculations performed
correctly, but no significant different in the total number

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of calculations performed or in the total number ofsteps. Also, there was no significant difference in taskrelated Oxy-Hb levels across age groups for each singletask (calculation and stepping). These results suggestthat the calculation task was more difficult for the older
participants compared with the younger group eventhough PFC activation was not significantly different
across the two age groups during the calculation task.
Schroeter [31] indicated that aging is generally associated with decreases in the hemodynamic response
within the frontal association cortex during cognitive
tasks. However, Reuter-Lorenz and Cappell [30] suggested older adult demonstrated overactivation in PFC
during a particularly challenging cognitive task. Our
results are in line with those reported by Reuter-Lorenz
and Cappell [30], in that older participants had increasing PFC activation during the higher cognitive load
imposed by the dual-task. It also seems likely that thecalculating/stepping dual-task used in this study was not
sufficiently challenging to be affected by the decreased
activation observed in older adults exposed to highly
complex tasks observed by Callicott et al. [29].
We also analyzed the relationship between brain
activity during dual-task performance and participant
executive function and attentional function, as measured by the TMT-B. Oxy-Hb values were negatively
correlated with the number of errors in TMT-B. Previous
studies suggested that PFC volume decreases with age[45] and that cerebral blood volume decreases withdementia [46]. Therefore, the relationship we observed
between lower PFC Oxy-Hb values and a greater numberof errors on the TMT-B test may reflect a decrease inbrain function due to aging-related cognitive decline orincipient dementia. Moreover, our result demonstrated asignificant negative correlation between dual-task performance and TMT-B scores among the older study participants. Montero-Odasso et al. [47] have demonstrated
that dual-task performance correlates with TMT-B
performance. Successful dual-task performance requires
attentional function and working memory. Decreases inthese functions have been associated with decreased PFC
activation in older adults.
There were some limitations in this study. First,
because of limitations imposed by the measurement
environment, this study used stepping in a chair as aphysical activity task. Second, previous study has
shown that elderly people with dementia demonstrate
reduced brain activation during a cognitive task compared with individuals without dementia [48]. All participants in this study, both older and younger, werecognitively intact so it is not possible to extrapolatethese results to populations of older adults with preexisting changes in cognitive ability. Finally, while ourstudy might suggest that structured dual-task activity

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facilitates PFC activation in older adults, future study
will need to clarify whether dual-task training can leadto facilitated PFC activation in older adults enablingthem to maintain cognitive function.

Conclusions
In conclusion, both younger and older participants showedsignificantly greater PFC activation during the dual-task
compared to either of the tasks in isolation. As a group,
older participants demonstrated higher peak Oxy-Hb andlonger PFC activation during the dual-task compared with
their younger counterparts. This result indicates that dualtask activity imposes a greater cognitive load on older individuals and performing the dual-task more strongly affectedchanges in brain activation among the older group. A significant negative correlation between PFC hemodynamic
activation during dual-task and executive-attentional function in older participants was observed. Therefore, our findings suggest that the increased cognitive load induced bydual-task activity leads to higher PFC activity in older adults
and that higher levels of increased activation during thedual-task are associated with a significantly lower error rateon the TMT-B test. It seems possible that, in the therapeutic environment, appropriately designed dual-task training may be a useful tool for the prevention or delay ofsome aspects of cognitive decline. Further research is warranted to determine how best to design dual-task interventions for vulnerable populations, as well as to assess thevalue of such interventions on the maintenance of cognitiveand functional ability as individuals grow older.
Abbreviations
PFC: Prefrontal cortex; NIRS: Near-infrared spectroscopy; TMT: Trail-Making
Test; TMT-B: Trail-making test part B; Oxy-Hb: Oxygenated hemoglobin;
Deoxy-Hb: Deoxygenated hemoglobin; Total-Hb: Total hemoglobin;
IGF-I: Insulin-like growth factor-1; ROI: Region of interest;
MMSE: Mini-mental state examination.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
HO was the lead writer of this manuscript and has made study design,acquisition of data, or analysis and interpretation of data. SO had a majorrole in the conception and design of the study, supervised all aspects of thestudy's implementation. KS and EBS had assisted the data interpretation andhad contributed to the writing of the manuscript. All authors read andapproved the final manuscript.
Acknowledgements
We gratefully acknowledge the assistance of the Yuyunosato facility staff(Yuyunosato, in Japan) in recruiting participants for this study.
Author details
1
Graduate School of Health Sciences, Seirei Christopher University, 3453
Mikatahara-Cho, Hamamatsu-City, Shizuoka 433-8558, Japan. 2Department ofhealthcare, Kansai University of Health and welfare science, 3-11-1,
Asahigaoka, Kashiwara-City, Osaka 582-0026, Japan. 3Johns Hopkins School of
Medicine, Center for Surgical Trials and Outcomes Research, 600 N. Wolfe St,
Baltimore, MD 21205, USA.

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Received: 14 July 2012 Accepted: 29 November 2012
Published: 18 January 2013
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doi:10.1186/1471-2202-14-10
Cite this article as: Ohsugi et al.: Differences in dual-task performanceand prefrontal cortex activation between younger and older adults.
BMC Neuroscience 2013 14:10.

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