World Journal of Neuroscience, 2011, 1, 19-27
doi:10.4236/wjns.2011.12003 Published Online August 2011 (http://www.SciRP.org/journal/wjns/ WJNS ).
Published Online August 2011 in SciRes. http://www.scirp.org/journal/W JNS
Neural correlates of focused attention in cognitively normal
older adults
Jennifer R. Bowes1, Patr ick Stroman 1,2,3, Angeles Garcia1,4
1Centre for Neuroscience Studies, Queen’s University, Kingston, Canada;
2Department of Diagnostic Radiology, Queen’s University, Kingston, Canada;
3Department of Physics, Queen’s University, Kingston, Canada;
4Department of Medicine, Queen’s University, Kingston, Canada.
Received 28 April 20 11; revised 1 8 May 2011; accepted 22 Jul y 2011.
ABSTRACT
Focused attention (FA) is among the cognitive func-
tions that decline with aging. The Stroop task was
used to investigate the neural correlates underlying
FA in cognitively normal older adults. Twenty-one
participants underwent a novel functional magnetic
resonance imaging (fMRI) verbal Stroop task para-
digm. Colour words were printed in an incongruent
ink colour. Series 1 consisted of four blocks “Read
the word” followed by four blocks “Say the colour of
the ink”; Series 2 alternated between the two condi-
tions. Functional data were analyzed using SPM5 to
detect anatomical areas with significant signal inten-
sity differences between the conditions. Within-group
analyses of the “Say the colour of the ink” minus
“Read the word” contrast yielded significant activa-
tion in the left supplementary motor area, bilateral
inferior frontal gyrus, bilateral precentral gyrus, left
insula and right superior frontal gyrus (p < 0.05, un-
corrected). These results, using verbal responses, are
consistent with previous manual modality Stroop-
fMRI studies in older adults. Verbal responses may
provide a more suitable modality for older adults and
certain patient populations.
Keywords: fMRI; Focused Attention; Stroop
1. INTRODUCTION
There is a growing interest in studying cognitive do-
mains, such as attention and inhibitory control, which
decline during the aging process. Older adults appear to
be more susceptible to cognitive interference than y-
ounger adults [1] and the frontal lobe, which is instru-
mental in exercising attention control, is susceptible to
some of the earliest and more rapid pathological changes
that occur in the aging brain [2]. Consequently, patho-
logical changes in the frontal lobe may contribute to the
increased susceptibility of older adults to cognitive in-
terference. More specifically, attention plays a critical
role in restricting the sensory input load that enters our
processing system [3], and attentional control is engaged,
most importantly, in times of cognitive conflict [4]. Fo-
cused attention (FA) biases the information we are ex-
posed to by enhancing task-relevant information, and is
used as a measure of the ability to inhibit irrelevant in-
formation [5]. In order to understand the changes that
occur with aging, and with diseases such as Alzheimer ’s
Disease (AD), it is therefore very important to under-
stand the changes that occur in the processes that control
attention.
The Stroop test [6] is a well-known experimental para-
digm that introduces cognitive conflict by presenting
colour names printed in a non-matching (incongruent)
ink colour, and is considered the gold standard for as-
sessment of FA. Cognitive interference reveals itself in
the Stroop task by an increase in response latency and/or
higher error rate when naming the ink colour [1,4].
However, the information that can be obtained about at-
tentional processes may be significantly enhanced by
combining the Stroop task with functional magnetic
resonance imaging (fMRI). Finding the ne ural substr ates
that underlie the Stroop effect may advance our under-
standi ng of how humans maintain attention and perform
the Stroop task [7]. The high spatial resolution and non-
invasive nature of fMRI makes it a valuable tool for
identifying the brain regions mediating FA. Initial Stroop-
fMRI studies in young adults have provided the founda-
tion to allow further investigations into the functional
processes in healthy aging. However, the means by
which we study the cognitive processes may require dif-
ferent approaches based on the demographics of those
being studied. While Stroop-fMRI studies in young

J. R. Bowes et al. / World Journal of Neuroscience 1 (2011) 19-27 20
adults have employed both verbal and manual response
modalities, only the manual button press modality has
been used with older adults [8-10]. By both self-report
and performance, older adults have more difficulty using
the button-box than the young adults [10]. The button-
box modality adds additional cognitive demands by re-
quiring subjects to remember which button corresponds
to which colour stimuli. This modality may add task
difficulty disproportionately for older adults.
Just as cognitively normal older adults appear suscep-
tible to cognitive interference, pathological conditions
such as AD interfere with cognitive function that in-
crease susceptibility to cognitive interference. An as-
sessment of cognitive functioning in older adults and
certain patient populations, such as those diagnosed with
AD and mild cognitive impairment (MCI), are an im-
portant part of clinical care. The Stroop task is among
the tools used in a clinical setting to assess cognitive
function, specifically FA, but has also been studied ex-
tensively in experimental paradigms. If cognitively nor-
mal older adults report difficulty during a manual mo-
dality Stroop-fMRI paradigm, one might expect that pa-
tients with cognitive impairments, such as those diag-
nosed with AD, would find such a paradigm even more
difficult. In order to gain a better understanding of the
neural mechanism of FA in these populations, an ex-
perimental paradigm suitable to the cognitive abilities of
such persons must be applied in order to more accurately
ascertain that the cognitive function of FA is being cap-
tured. The use of verbal modality in Stroop-fMRI para-
digms may be a suitable paradigm that allows one to
investigate FA in older adults and in patient populations
such as AD and MCI. In order to extrapolate the findings
from experimental studies to the clinical setting, one
must minimize the differences in the administration of
the Stroop task across the two settings. The use of the
verbal response modality in the fMRI task would be
consistent with the verbal responses required in the pa-
per version of the Stroop task that is used in clinical set-
tings.
Although many variations of the Stroop task paradigm
exist, the majority of Stroop-fMRI studies have in-
structed subjects to name the ink colour across incon-
gruent, congrue nt, neutral or non-lexical stimuli to yield
brain regions underlying Stroop interference. However,
in fMRI, to best determine the brain regions underlying a
given cognitive process, the differences between the two
conditions being compared should be minimized as to
isolate the cognitive process of interest. In the current
study, the colour word stimuli presented are identical in
all incongruent trials, with the only difference being the
instructions given to the subject (“Read the word” or
“Say the colour of the ink”). In this way, the current ex-
perimental paradigm isolates the cognitive process of FA
better than the previous Stroop-fMRI studies in older
adults, and in doing so, improves the similarity between
the fMRI Stroop task and the original paper version of
the Stroop task.
The current study offers a novel Stroop-fMRI para-
digm that employed a verbal response modality using
incongruent colour-word trials to yield the Stroop effect
by contrast ing reading the word from saying the ink co-
lour in cognitively normal older adults.
2. METHODS
2.1. Subject Population
The study was approved by the University Research
Ethics Board. All subjects gav e written informed consent
prior to undergoing any study procedures. Twenty-one
cognitively normal, independent community dwelling
older adults (13 women, 8 men) were recruited. Subjects
were all native or highly proficient English-speaking
volunteers between the ages of 60 and 85 years (mean
age  SD, 72 ± 8), who could safely undergo a MRI,
with no colour blindness, neurological or other medical
conditions that could interfere with the task protocol.
2.2. Cognitive Assessment
Subjects underwent a neuropsychological test battery to
assess their general cognitive function including the fol-
lowing tests : the Mini-Mental State Examinatio n (MMSE)
[11], the Montreal Cognitive Assessment (MoCA) [12],
the Mattis Dementia Rating Scale (DRS) [13], the
Stroop test, the Trail Making Test- Part B (TMT-B) [14],
and the California Verbal Learning Test-Version II
(CVLT-II) [15]. Subjects were considered to have nor-
mal cognitive abilities with the following test scores:
MMSE  26, MoCA  26, DRS  123, Stroop colour-
word score of > 65 and CVLT-II verbal recall sub-scores
> 1.5 SD below the mean for age, sex and years of edu-
cation.
2.3. fMRI Experimental Task
The fMRI experiment was carried out at the Queen’s
University Research MRI Facility. The Stroop test used
was an adaptation from the word-colour incongruent
task taken from the paper version of the Stroop test. The
four colour word stimuli used in the experiment were:
blue, green, tan and red. Colour word stimuli were pre-
sented visually via back projection onto a screen that
was viewed through a mirror attached to the head coil of
the scanner. The presentation of the colour word stimuli
was run using MatlabR2006b (The Mathworks, Natick,
MA). An MR-compatible microphone with noise can-
cellation was placed in front of the participant’s mouth
to record the verbal responses to the presented colour
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J. R. Bowes et al. / World Journal of Neuroscience 1 (2011) 19-27 21
performed twice and h erein referred to as Series 2a and 2 b. word stimuli. Subjects were instructed to speak aloud,
but quietly, and without excessive enunciation, in an
attempt to minimize head motion while speaking. Verbal
reminders to keep their head still and limit any body
movements were made at short rest intervals between the
series, if movement for a given subject was a concern.
Subjects were given headphones to wear to reduce the
noise of the MR scanner and to provide a means to
communicate with the subject throughout the experiment.
Padding was placed between the outside of headphones
and the sides of the head coil to reduce the opportunity
for the subjects to move their head. The experimental
protocol was carried out as a block design with four
functional series’ as displayed in Figure 1. Each block
was 28 seconds and consisted of 16 colour word stimuli,
each of which was presented for 1.75 seconds. Each
block was separated by a 14-second rest period. Series 0
consisted of 4 blocks with colour word stimuli presented
in black ink and participants were instructed to read the
word. The instructions “Read the word” preceded the
commencement of the first block with a fixation cross
displayed during the remaining rest periods. A total of 91
images were acquired with a sequence scan time of ap-
proximately 3 minutes. Series 1 and 2 consisted of 8
blocks with colour word stimuli presented in an incon-
gruent ink colour with the rest period preceding each
block displaying the instructions for the subsequent
block. A total of 175 images were acquired with a se-
quence scan time of approximately 6 minutes for each
Series 1 and 2. In Series 1, participants were instructed
to “Read the word” (herein referred to as “Word” condi-
tion) in the first 4 blocks, and instructed to “Say the
colour of the ink” (herein referred to as “Colour” condi-
tion) in the last 4 blocks. In Series 2, blocks alternated
between “Word” and “Colour” conditions. Series 2 was
2.4. Image Acquisition
All imaging was acquired on a 3 Tesla Siemens Magne-
tom Trio MRI system (Siemens Medical Systems, Er-
lange n, Ge r ma n y) i n c o nj unc t i o n wit h a 1 2 -c ha nnel he ad
coil. Motion correction software was used during scan-
ning, and in the subsequent data analysis. Structural and
functional sequences were acquired. A 176 slice, high-
resolution anatomical scan was acquired with a T1-
weighted 3D, MP-RAGE sequence (single shot, ascend-
ing sequence in the sagittal plane with TR = 1760 msec,
TE = 2.2 msec, flip angle = 9˚, FoV = 256 mm, voxel
size = 1 mm3). Functional data was acquired along the
anterior commissure-posterior commissure (AC-PC) line
with blood oxygenation level dependent (BOLD) T2*-
weighted echo planar imaging. Thirty-two axial slices
(TR = 2000 msec, TE = 30 msec, flip angle = 78˚, FoV =
211 mm, voxel size = 3.3 mm cubic voxels) were ac-
quired providing whole-brain coverage using interleaved
acquisition.
2.5. Data Analysis
Statistical analysis on demographics, cognitive assess-
ment and performance accuracy was performed using
SPSS, Version 17.0 (SPSS Inc., Chicago, IL). Subject’s
verbal responses to colour word stimuli were recorded
for analysis of performance accuracy on the Stroop-
fMRI task. Condition blocks with less than 75% accu-
racy were excluded from fMRI analysis. Errors were
classified as incorrect, missed or corrected responses.
Spatial pre-processing and statistical analysis of the
imaging data was carried out using SPM5 (Wellcome
Department of Cognitive Neurology, University College
Figure 1. Stroop- fMRI experimental paradigm. In Series 0, 4 blocks of colour word stimuli were
present ed in bl ack ink and p arti cipan ts were asked to read th e word. The first rest period displ ayed
the instru ction of “Read the word”; t he remaining rest peri ods displayed a fixation cross. In Series
1, 2a, and 2b presented 8 blocks of colour word stimuli presented in an incongruent ink colour,
with the rest period displaying the instructions to the subsequent condition block. In Series 1, par-
ticipants were asked to ‘Read the word’ for the first 4 blocks, and to “Say the colour of the ink”
for the last 4 blo cks. Series 2a and 2b are identical, with bl ocks alternated between t he “Read the
word” and “Say the colour of the ink” conditions.
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J. R. Bowes et al. / World Journal of Neuroscience 1 (2011) 19-27 22
London, England). The first two functional scans in each
series were discarded from the analyses to allow the lon-
gitudinal magnetization to reach a steady state. The fol-
lowing pre-processing steps were carried out: realign-
ment, co-registration, segmentation, normalization and
smoothing. First, functional T2*-weighted images were
spatially realigned to the first analyzed volume scanned
in the run using a six-parameter rigid-body transforma-
tion to compute a mean functional image. Next, the high
resolution T1-weighted structural scan was co-registered
to the mean realigned functional images. SPM5 com-
bines segmentation, spatial normalization and bias cor-
rection in a unified model approach [16]. The segmented
images were then normalized into the standard stereotac-
tic space of the Montreal Neurological Institute (MNI)
template. Lastly, the functional images were smoothed
with a Gaussian kernel of 8 mm × 8 mm × 8 m full
width at half maximum. A 128-second temporal high
pass filter (with 1/128 seconds (0.0078 Hz) as the fre-
quency cut off) was applied t o the functional data to e x-
clude low frequency fluctuatio ns and artifacts. Statistical
analysis was performed using the univariate approach of
the general linear model [17] whereby the box-car ref-
erence function is convolved with the hemodynamic
response function to account for the delay in the BOLD
signal. For each subject, a design matrix was created
with the rest periods, correct “Word” blocks and correct
“Colour” blocks applied as regressors, in addition to the
six realignment parameters. Error blocks were repre-
sented as separate regressors in the design matrix, though
not used in any contrasts. Voxel-wise statistical analysis
was then carried o ut to dete rmine which voxels were acti-
vated by the different experimental conditions. Fixed-
effects analysis was applied to each participant resulting
in statistical parametric maps (SPMs) for every contrast
of interest, using a significance threshold of p = 0.001,
uncorrected for multiple comparisons. Individual SPMs
from each participant were then pooled together and
entered into a random-effects analysis. A one- sample
t-test was applied to in vestigate the within-group activa-
tion level with a significance threshold of p = 0.05, un-
corrected for multiple comparisons. To control for false
positives, a spatial extent cluster threshold of 3 voxels
was applied. The coordinates of voxels that survived the
statistical threshold were entered into MRICro software
[18], which uses an automated anatomical labeling
(AAL) template [19] to report the localization of the
activation. Significant voxels reported in SPM5 are re-
ported in MNI space, and the AAL template was created
based on the anatomical parcellation of the spatially
nor malized si ngle- subj ect, se gmented high re solutio n T1
volume provided by MNI. Realignment parameters of
motion-corrected and non motion-corrected functional
data were used to estimate subject motion during the ex-
perimental task.
3. RESULTS
3.1. Behavioural Results
Demographic descriptives and mean neuropsychological
test battery scores are listed in Table 1. In the paper ver-
sion of the Stroop task administered as part of the test
battery, all subjects were significantly better reading the
word than nami ng the c olour of t he ink (p < 0.001).
Both non-motion corrected and motion corrected data
were viewed to inspect subject motion parameters. The
average subject movement was estimated based on the
rotation about and the translation along each of the 3
coordinate axes (x, y, and z). There was a mean (SD)
translation of 2.85  1.193 mm and a rotation of 2.964 
1.454 degrees for non-motion-corrected acquired images.
For the motion corrected acquired images, the mean (
SD) translation was 1.786  0.681 mm and a rotation of
1.905  0.785 degrees.
Performance accuracy during the Stroop-fMRI ex-
periment was assessed. The mean (±SD) numberof total
errors across all series was 8.00 ± 6.834. The mean (±
SD) number of errors in Series 1, Series 2a and Series 2b
were 1.38 ± 2.397, 3.57 ± 4.976 and 3.05 ± 4.511, re-
spectively. There were no significant differences in the
numbers of errors between Series 1 and 2a (p = 0.107),
Series 1 and 2b (p = 0.144) and Series 2a and 2b (=
0.725). The mean (±SD) numbers of errors in each of the
“Word” and “Colour” conditions were 2.90 ± 3.961 and
4.86 ± 4.983, respectively. Across all of the series, there
Ta b l e 1 . Demographic descriptives and mean neuropsychologi-
cal test battery scores.
Cognitively Normal Older
Adults N = 21 Mean (SD)
Gender (M:F) 8:13
Age (years) 71.24 (5.682)
Education (years) 16.10 (4.170)
MMSE 29.62 (0.498)
MoCA 27.00 (1.949)
DRS
Total Score 141.90 (2.047)
Stroop
Word Score
Colour Score
112.00 (0.000)
96.24 (11.528)
TMT-B (seconds)* 86.00 (20. 039)
CVLT-II
SDFR Raw Score
LDFR Raw Score
10.191 (3.750)
10.429 (3.749)
M = Male; F = Female; MMSE = Mini-Mental State Examination; MoCA =
Montreal Cognitive Assessment; DRS = Dementia Rating Scale; TMT-B=
Trail Making Test-Part B; CVLT-II = California Verbal Learning Test-
Version II; SDFR = Short Delay Free Recall; LDFR = Long Delay Free
Recall; *N = 20.
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J. R. Bowes et al. / World Journal of Neuroscience 1 (2011) 19-27 23
were no significant differences in error rates between the
“Word” and “Colour” conditions (p = 0.144). When the
number of errors by condition is stratified by series, as
seen in Figure 2, only Series 1 showed significantly
more errors in the “Colour” condition than in the ‘Word’
condition (p = 0.026). The mean (SD) number of in-
correct, corrected, and missed responses were 1.286 
2.825, 0.794  1.894, 0.587  1.11 6, respect ively.
3.2. Imaging Results
The main contrast of interest was the incongruent “Col-
our” condition against the “Word” condition yielding
brain areas more activated in the “Colour” than in the
“Word” condition. The within-group analysis of the in-
terference condition across Series 1, 2a and 2b yielded
greater activation in the left supplementary motor area
(SMA), bilateral precentral gyrus, right pars opercularis
of the inferior frontal gyrus (IFG), left insula, and right
supe rior frontal gyrus (p = 0.05, uncorrected for multi-
ple comparisons) as listed in Table 2. The brain areas
significantly more active in the “Colour” condition com-
pared to the “Word” condition are displayed on the SPM
Figure 2. Mean number of errors by condition type across the
incongruent series. Mean number of errors by condition type
across the incongruent series (S eri es 1, Series 2a an d Series 2b)
for the cognitively normal older adults. There was a significant
difference in the number of errors between the “Read the
word” and “Say the colour of the ink” co ndition for S eries 1 (p
= 0.026), but no significant differences between conditions in
either Series 2 a (p = 0.221) or Series 2b (p = 0.43 6). ( * = st atis-
tically significant; ns = not significant).
Ta b l e 2. Brain areas significantly more active in the “Colour”
condition than in the “Word” condition from the within-group
analysis of the cognitively normal older adult group.
MNI coordinates in talarach
Space (mm)
Region Side x y z
T Z-score
Supplemerntary
motor area L –9 9 48 3.893.32
–42 3 27 3.202.84
L –36 0 36 3.152.81
Precer tral gyru s R 60 9 39 2.782.53
48 48 18 6 2.622.40Inferior frort al
gyrus, pars oper-
cularis L –27 21 6 2.502.40
24 12 69 2.432.25Insu la Superior
frontal gyrus R 27 3 66 1.971.87
Figure 3. Overlay of brain activation of the within-group ana-
lysis for the “Say the col our of the ink” minus “Read the word”
contrast. An overlay of brain regions on the SPM glass brain
(left) and on an anatomical template (right) showing increased
activity in the “Say the colour of the ink” than in the incon-
gruent “Read the word” by the cognitively normal older adult
group (p < 0.05, uncorrected).
in Figure 3 (p = 0.05, uncorrected for multiple com-
parisons). The main contrast “Colour” minus “Word” for
Series 1 yielded significant activation in the left pars
opercularis of the IFG, right insula, left inferior and su-
perior parietal cortex, left lingual, right middle and supe-
rior frontal gyrus and the right precentral gyrus. For the
Series 1 main contrast of interest, only the left pars op-
ercularis of the IFG survived the statistical threshold of p
= 0.001. There were no brain regions for either Series 2a
or 2b main contrast of interest that survived a p = 0.001
statistical threshold. The contrast comparing Series 0
“Word” condition with Series 0 rest condition (fixation
cross) yielded significant brain activation in expected
speech production and reading brain regions, including
the precentral gyrus, SMA, middle frontal gyrus, and
lingual gyrus with pred ominantly left hemisp here activa-
tion.
4. DISCUSSION
This is the first study to investigate the neural correlates
of FA using a Stroop-fMRI task paradigm in cognitively
normal older adults using verbal responses rather than a
manual button press modality. The main contrast of in-
terest for the incongruent trials, “Colour” minus the
“Word”, elicited increased activation including the SMA,
precentral gyrus, and IFG. The results of the current
study are consistent with brain regions activated in pre-
vious manual button press modality Stroop-fMRI studies
in older adults [8-10]. Similar brain regions within the
neural network of FA of the current verbal modality
study with previo usly publis he d manual modalit y studie s,
suggest the current study’s novel verbal modality Stroop-
fMRI task offers a suitable paradigm to investigate the
neural correlates of FA. Furthermore, the task was per-
formed well by the cognitively normal older adults.
4.1. Behavioural Results
In the paper version of the Stroop test administered as
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J. R. Bowes et al. / World Journal of Neuroscience 1 (2011) 19-27 24
part of the neuropsychological test battery, as expected,
subjects were significantly better at reading the word
than naming the colour of the ink. Interestingly, in the
Stroop-fMRI experimental task, when errors were col-
lapsed across all series, subjects did not make signifi-
cantly more errors in the “Colour” condition than in the
“Word” condition. This is likely a reflection of the ex-
perimental design, although overall, very few errors
were made during the Stroop-fMRI task. In Series 1,
which consisted of four blocks of “Word” followed by
four blocks of “Colour”, subjects made significantly
more errors when naming the ink colour. Whereas, in
Series 2a and 2b, which consisted of alternating “Word”
and “Colour” conditions, there was no significant dif-
ference in errors between the two conditions, and may
reflect the difficulty subjects had in remembering which
set of instructions was given. The majority of the
“Word” errors were made in the alternating Series 2a and
2b. That is, prior to the introduction of the “Colour”
condition, reading the word is a fairly automatic process
for the subjects. However, once the “Colour” condition
is introduced, reading the word becomes less automatic,
and FA is likely required for both conditions because
what is considered the irrelevant colour dimension,
changes each block.
4.2. Imaging Results
The main contrast of interest for the current study was
the subtraction of the incongruent “Word” condition
from the incongruent “Colour” condition. Significant
activation was observed in the left SMA, bilateral pre-
central gyrus, and right pars opercularis of the IFG, left
insula and right superior frontal gyrus. The neuroimag-
ing results of the study are in keeping with the results
from previous Stroop-fMRI studies of older adults. Com-
mon activated regions between the work of Zysset et al.
[9] and the current findings include the IFG and superior
frontal gyrus. In the Stroop-fMRI study of Milham et al.
[8], older adults activated a network of structures in-
cluding the IFG, as found in the current study, and the
SMA showed increased activity specific to the presence
of co nflicti ng colour i nfor mat ion. The study’s findi ng of
right frontal gyri was also found in the Stroop-fMRI
study of Langenecker et al. [10].
Similar regions of brain activation were found be-
tween the current study and previous Stroop-fMRI stud-
ies of older adults despite methodological differences.
Chief among the methodological differences was the use
of a verbal response modality in this study. The greatest
concern with use of verbal responses in an experimental
paradigm is the increased susceptibility to motion arti-
fact inherent with verbal responses. However, means to
account for and correct some of the movements made by
subjects during the experimental task were undertaken to
min imi ze subj ec t mo tio n and to mi ni miz e it s effe ct on
the imaging data in the present study, as described in the
Methods section. Motion-corrected software, which in-
cluded the automated image registration for motion cor-
rection of fMRI time-series during the pre-processing of
the functional data, was also applied to reduce some of
the effects caused by changes in position between suc-
cessive images. Although uncorrected motion can con-
found functional data by causing signal changes, it is
those voxels that lie close to tissue boundaries that are
most susceptible [20]. Given our knowledge of the neu-
ral substrates that underlie the Stroop task, the brain re-
gions expected to be involved with this task are, for the
most part, not in close proximity to areas of high con-
trast or tissue boundaries. Analyzing the motion pa-
rameters and visually inspecting the motion data allows
one to consider the influence the motion has on the func-
tional results. Subject inter-scan movement can be esti-
mated using the motion parameters obtained from the
spatial realignment step in pre-processing, whereby each
image in the time series is compared to the first, refer-
ence image of that time series. The time series images of
translation and rotation motion parameters were visually
inspected to exclude any subject with excessive motion.
Given the verbal modality of the experimental task, ex-
cessive motion was considered if both translation and
rotation measures were >5 mm and degrees, respectively.
Using this cut-off criterion, no subjects were excluded
from the analysis. The motion-corrected functional data
were used in subsequent analyses and likely reflects the
influence of subject motion on the imaging results.
However, the non-motion corrected data provides the
best estimate of subject motion during the experimental
run. By decreasing the length of the experimental para-
digm and by giving more reminders to subjects to re-
main still, the motion parameters for the older adults
may be lowered to improve the integrity of the imaging
results.
The current study had a larger older adult sample size
than previous Stroop-fMRI studies by Milham et al. [8]
and Langenecker et al. [10]. The mean age of the older
adults in the current study (71 years) was comparable to
the mean age of older adults in the Langenecker et al.
[10] study (71.1 years) and just slightly older than those
in the Milham et al. [8] study (68 years). Among the
network of brain regions commonly activated by older
adults are the anterior cingulate cortex (ACC)/pre-sup-
plementary motor area (pre-SMA), middle, superior and
inferior frontal gyri, and superior and inferior parietal
lobules. Older adults have shown increased activation,
predominantly in the left hemisphere, in the prefrontal
cortex, pre-SMA and left inferior frontal gyrus relative
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J. R. Bowes et al. / World Journal of Neuroscience 1 (2011) 19-27 25
to younger adults. These results suggest that older adults
rely on, and recruit additional brain areas, particularly pre-
frontal regions during Stroop task performance [21].
Further more, Milham et al. [8], suggested that the parie-
tal cortex has greater involvement in younger than older
adults, with older adults reliant on the more anterior,
frontal brain regions. This is supported by the findings of
the current study where the majority of brain regions
underlying Stroop performance lay within the frontal
cortex. Implementation of cognitive control may rely on
modulation of bilateral inferior frontal regions [22] with
activation of the left inferior frontal region consistently
found in Stroop-fMRI studies. The inferior frontal region
may reflect phonology as this area becomes more active
when viewing words and during the retrieval, selection,
maintenance or evaluation of semantic knowledge [23].
The inferior frontal region is also home to Broca’s area
for speech production, and activation of this region in
Stroop interference may reflect the response selection
competition involving speech articulatory processes [24].
Stroop interference appears to be mediated by competing
subvocal articulatory responses in both manual and ver-
bal response modalities suggesting this mediation is not
specific to overt speech paradigms [24]. In a positron
emission tomography (PET) study, only the left IFG was
consistently activated during the interference condition
[25]. The left inferior precentral sulcus is located adja-
cent to the pars opercularis of the IFG and is thought to
play a critical role in processing incongruent Stroop
stimuli [24, 25]. The precentral gyrus may correspond to
the frontal eye fields [26], which have been shown to be
an important area in top-down allocation of attention
[27]. The SMA, important for the initiation and control
of motor and speech functions [28], and the pre-SMA,
involved in encoding and selection of word information
[29], are regions found within the medial frontal cortex
and have been found to be activated in numerous Stroop-
fMRI studies [8,10,30,31]. Located within the pre-SMA
region is the superior frontal gyrus, which is also fre-
quently activated in the incongruent Stroop condition [8,
10,30,32]. According to Taylor et al. [25], the cingulate
sulcus/SMA region is involved in resolving response
conflict. Brain regions involved in response generation
include the cerebellum, SMA and precentral gyri [32].
Given the current Stroop task whereby subjects are re-
quired to initiate a verbal response, the activation of the
SMA and precentral gyri support the role these regions
may play in response generation. The insula is believed
to be involved in verbal working memory and selective
attention tasks [7] and contributes to cognitive control
[9].
Among the early neuroimaging studies of the Stroop
task, the Stroop effect almost unanimously activated the
ACC. However, as the Stroop task became used in more
studies, and with variations in its paradigm used, the
ACC was not consistently activated. This lead Mead et
al. [24] to suggest that demonstrating ACC activation
may depend on methodological factors in the experi-
mental design. In the current study, the main contrast of
interest for Stroop interference did not detect activity
within the ACC. Contrasts comparing incongruent col-
our words to non-lexical stimuli such as colour blocks,
hatches or crosses have shown more consistent ACC
activation while contrasts with lexical stimuli, as in the
curr ent stud y, ha ve resul ted in less freq uent AC C activa -
tion [24]. Some authors have postulated that the atten-
tional demands are similarly enhanced on incongruent
and congruent trials [33], or that the ACC was activated
at approximately the same intensity across the incon-
gruent, congruent, and neutral conditions [24]. Further-
mor e , M il ha m et al. [8] showed that for older adults, the
mere presence of competing colour information of in-
congruent trials was enough to produce increases in the
ACC. The current experimental paradigm consisted
largely of incongruent trials, so if the presence of incon-
gruent trials alone produces ACC activation, contrasting
the two incongruent conditions will not reveal the com-
mon ACC activity in the two conditions. In addition,
lesion studies have demonstrated that in some patients
with extensive ACC damage, their Stroop performance
was unimpaired [21]. These results suggest that although
the ACC may be involved in mediating the Stroop effect,
it appears that Stroop task performance does not require
its activation to resolve the cognitive conflict presented
by the Stroop paradigm.
The current study used verbal responses and con-
trasted incongruent trials of “Read the word” from “Say
the colour of the ink” conditions in a Stroop-fMRI task
paradigm that more closely mimics the paper, clinical
administration of the Stroop task, and whose use of a
verbal modality, may be better suited to an older adult
population. Changes in cognitive function occur with
normal aging, but are exacerbated in pathological dis-
eases such as AD. Attentional deficits, including im-
pairments in FA, have been observed in patients with AD
and MCI [34]. Functional imaging studies with AD and
MCI patients would allow for the study of the neural
mechanisms underlying their reduced performance on
FA tasks such as the Stroop task. However, therein lies
the challenge of creating an experimental paradigm to
investigate the neural correlates of FA, that patients with
diminished cognitive functioning can comprehend and
perform as instructed. The Stroop-fMRI task was per-
formed well by the older adults, and suggests that this
experimental paradigm, with the use of verbal responses
instead of the more complicated manual responses, may
C opyright © 2011 SciRes. WJNS

J. R. Bowes et al. / World Journal of Neuroscience 1 (2011) 19-27 26
allow the neural correlates of FA in patients with patho-
logical diseases, such as AD to be investigated.
5. CONCLUSIONS
Combined with preventative measures to minimize mo-
tion and its effects on the resulting image data, verbal
responses may offer a more appropriate modality for use
in an older adult population. The novel Stroop experi-
mental paradigm employed in the current study found
similar regions of activation than previous Stroop-fMRI
studies of older adults using the manual response modal-
ity, sugge sting that despite a difference in modality used,
the results reveal the neural correlates of FA. Further-
more, the verbal task paradigm used in this study may
also be useful in studying the neural correlates of FA in
patient populations with known impairments of FA. The
use of incongruent colour words stimuli across both ex-
perimental conditions of the study may provide a means
to identify brain areas supporting FA, beyond those, such
as the ACC, which may activate upon the presentation of
conflicting information o f the incongruent word stimuli.
6. ACKNOWLEDGMENT
The study was supported by a Queen’s University CTAQ Endowment
Fund grant.
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