University Department of Psychiatry, Warneford Hospital, Oxford, UK
Correspondence: Professor PJ Cowen, Neurosciences Building, Warneford Hospital, Oxford OX3 7JX, UK Email: phil.cowen{at}psych.ox.ac.uk
None. Funding detailed in Acknowledgement.
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We previously found that children of parents with depression showed impaired performance on a task of emotional categorisation.
Aims
To test the hypothesis that children of parents with depression would show abnormal neural responses in the anterior cingulate cortex, a brain region involved in the integration of emotional and cognitive information.
Method
Eighteen young people (mean age 19.8 years) with no personal history of depression but with a biological parent with a history of major depression (FH+ participants) and 16 controls (mean age 19.9 years) underwent functional magnetic resonance imaging while completing an emotional counting Stroop task.
Results
Controls showed significant activation in the pregenual anterior cingulate cortex to both positive and negative words during the emotional Stroop task. This activation was absent in FH+ participants.
Conclusions
Our findings show that people at increased familial risk of depression demonstrate impaired modulation of the anterior cingulate cortex in response to emotionally valenced stimuli.
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It is possible to probe the function of the anterior cingulate cortex in humans using a modified emotional counting Stroop task where emotionally valenced words compete with the cognitive demands of the task.4 In healthy participants the emotional counting Stroop (ecStroop) activates the affective subdivision of the anterior cingulate cortex as measured by functional magnetic resonance imaging (fMRI).4 We therefore tested the hypothesis that, relative to age-matched controls, FH+ participants would show impaired activation in this subdivision during performance of the emotional counting Stroop.
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Participants were assessed on a number of measures of current emotional state, including the Mood and Feeling Questionnaire (MFQ),8 the Hospital Anxiety and Depression Scale (HADS)9 and the Perceived Stress Scale (PSS).10 We also administered the Parental Bonding Instrument (PBI)11 and the Life Events Rating Scale (LERS),12 which assesses threat and loss events in the past year and over the lifespan. All participants gave full informed consent to the study, which was approved by the local ethics committee.
Image acquisition
Imaging data were collected using a 1.5 T Siemens Sonata scanner located at
the Oxford Centre for Clinical Magnetic Resonance Research. Functional imaging
consisted of 35 T2*-weighted echo-planar image slices (repetition
time (TR) 3000 ms, echo time (TE) 50 ms, flip angle 90°, matrix
64x64, 3 mm isotropic voxels). To facilitate later co-registration of
the fMRI data into standard space, we also acquired a Turbo FLASH sequence (TR
12 ms, TE 5.65 ms, voxel size 1 mm3). The first two echo-planar
image volumes in each session were discarded to avoid T1
equilibration effects.
Emotional counting Stroop task
Participants were scanned while performing a modified version of the
emotional counting Stroop called the name the number of words
task.4 Word stimuli
were a subset drawn from a larger pool used in previous
research13
examining depression and anxiety, and selected to be either neutral (e.g.
mileage, molecule), physically threatening (e.g. fatal, accident), socially
threatening (e.g. worthless, inferior) or positive (e.g. generous,
achievement). Physically threatening and socially threatening words were
combined to generate a negative word category. Words were matched for word
length, frequency and imageability. (For further information see online Table
DS1 and
www.psy.uwa.edu.au/mrcdatabase/uwa_mrc.htm.)
Participants completed one run of the task with a total of 160 words being presented across 16 blocks. Four 20-word blocks of each stimulus type were presented in a pseudo-randomised order and interspersed with 20-s blocks of fixation, free of stimulus (no motor response) as baseline. Presentation of the four conditions was counter-balanced across participants and between the two groups. Participants completed 10 trials during each presentation block (stimulus presentation 1500 ms, intertrial interval 500 ms). For each trial, participants viewed between one and four identical words and were instructed to report (via keypad response) the number of words presented in each trial. Stimuli were presented on a personal computer using E-Prime (version 1.0; Psychology Software Tools Inc., Pittsburgh, Philadelphia, USA) and projected onto an opaque screen at the foot of the scanner bore, which participants viewed using angled mirrors. Both accuracy and reaction times were recorded by E-Prime.
Functional MRI data analysis
Functional MRI data were preprocessed and analysed using the functional
magnetic imaging of the Brain Software Library (FSL version 3.3;
www.fmrib.ox.ac.uk/fsl),
implemented in Linux SUSE, version
9.1.14
Preprocessing included within-participant image
realignment,15
non-brain
removal,16 spatial
normalisation to a standard template (Montreal Neurological Institute (MNI)
152 stereotactic
template)17 using
an affine procedure and spatial smoothing using a Gaussian kernel (5 mm
full-width, half-maximum). The time series in each session was high pass
filtered (to a maximum of 0.007 Hz).
Analyses of data from individual participants were computed using the general linear model with local autocorrelation correction.18 Three explanatory variables were modelled: neutral, positive and negative words. In addition, temporal derivatives were included in the model as covariates of no interest to increase statistical sensitivity. All variables were modelled by convolving each block with a haemodynamic response function, using a variant of a gamma function (i.e. a normalisation of the probability density function of the gamma function) with a standard deviation of 3 s and a mean lag of 6 s.
Individual participant data were combined at the group level using full mixed effects analyses.19 Significant activations were identified using cluster-based thresholding of statistical images with a height threshold of Z=2.0 and a (corrected) spatial extent threshold of P<0.05.20 Approximate Brodmann areas (BA) were identified by transformation of MNI coordinates into Talairach space (additional information available at www.mrc-cbu.cam.ac.uk/Imaging).
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View this table: [in a new window] | Table 1 Group demographic and psychosocial measures |
Functional MRI data
Because of our interest in activation differences between FH+ participants
and controls, we report significant between-group comparisons (thresholded at
Z=2.0, P=0.05, whole brain corrected) rather than effects of
task performance within the two groups. For the orthogonal contrast negative
words v. neutral words, we observed significantly greater activation
in controls in the anterior cingulate cortex, medial frontal and right
superior frontal gyrus (BA 24/10 and 9 respectively), left middle frontal
gyrus (BA 8/6) and left caudate nucleus and bilateral activation in the
inferior parietal lobe (BA 7) (Table
2). Comparing positive words with neutral words, controls had
significantly greater blood-oxygen-level dependent (BOLD) response in the
right anterior cingulate (BA 24), left thalamus, left superior frontal gyrus
(BA 10) and left precuneus (BA 19) (Table
3).
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View this table: [in a new window] | Table 2 Regions showing increased activation in controls compared with FH+ for the linear contrast negative v. neutral words |
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View this table: [in a new window] | Table 3 Regions showing increased activation in controls compared with FH+ for the linear contrast positive v. neutral words |
Given our a priori hypothesis regarding the role of the affective subdivision of the anterior cingulate cortex in the emotional counting Stroop task, we focused subsequent analyses on this brain region. To examine groupxemotion interactions we first extracted percentage signal change from the significant clusters of this subdivision identified above in the whole brain analysis (negative v. neutral words and positive v. neutral words). Further statistical analysis was implemented using a repeated measures analysis of variance (ANOVA) model with group (FH+ v. controls) as the between-participant factors (FH+ v. control) and word type (positive/negative/neutral words) as the within-participant factor for all participants. Significant interactions were followed up using simple main effects (independent and repeated-samples t-tests) to elicit the degree of this differential activation.
Negative v. neutral word contrast
For this contrast we observed a significant groupxword type
interaction (F(1,32)=12.63, P=0.001) extending
from the affective subdivision of the anterior cingulate cortex (BA 24/32)
anteriorly to the medial prefrontal cortex (BA 10). As reported
previously,4
controls showed a significantly greater activation to negative emotional words
relative to neutral (repeated-samples t(15)=3.58,
P=0.001). By contrast, FH+ participants showed no differential
response between neutral and negatively valenced words (repeated-samples
t(15)=1.29, P=0.22). There was a trend for
controls to have a greater deactivation relative to baseline to neutral words
compared with FH+ participants (independent samples
t(32)=1.97, P=0.06)
(Fig. 1). Essentially the same
findings were obtained when the negative words were analysed separately as
physically threatening and socially threatening words (data not shown).
![]() View larger version (26K): [in a new window] [as a PowerPoint slide] |
Fig. 1 Modulation of the anterior cingulate affective subdivision during
performance of the emotional counting Stroop. (a) Axial, coronal and sagittal
images depicting significantly increased activation in controls for the linear
contrast negative v. neutral words (images thresholded at
Z=2, P=0.05 (corrected)) in medial prefrontal cortex
extending from the rostral anterior cingulate (BA 24/32) anteriorly to medial
prefrontal cortex (BA 10). Foci of activation, x=2, y=54,
z=–4. (b) Neural response (expressed as % signal change)
extracted from the above significant cluster to negative and neutral words.
Error bars show standard error of the mean. FH+, young person with parent with
depression who has not had depression themselves.
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![]() View larger version (25K): [in a new window] [as a PowerPoint slide] |
Fig. 2 Modulation of the anterior cingulate affective subdivision during
performance of the emotional counting Stroop. (a) Axial, coronal and sagittal
images depicting significantly increased activation in controls for the linear
contrast positive v. neutral words (images thresholded at Z=2,
P=0.05 (corrected)). Foci of activation, x=2, y=26,
z=18 (BA 24/32). (b) Neural response (expressed as % signal change)
extracted from the above significant cluster in anterior cingulate affective
division to positive and neutral words. Error bars show standard error of the
mean. FH+, young person with parent with depression who has not had depression
themselves.
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Limitations
An important limitation of the study is that we did not systematically
conduct personal psychiatric interviews with relatives in either FH+ or
control groups and it is therefore possible that some of the parents in the
FH+ group did not have depression or that some parents in the control group
did. Presumably, however, misclassifications of this kind would tend to
decrease rather than increase biological differences between the two groups.
In addition, we have previously shown in a larger study that FH+ participants
identified in this way have increased waking salivary cortisol secretion
relative to
controls.21 It has
been estimated that by young adulthood up to 40% of children of parents with a
clinical mood disorder will have suffered a personal episode of
depression;22
however, the FH+ participants in the current study did not differ from
controls in terms of current affective symptomatology and levels of perceived
stress. In addition, albeit on limited data, it does not appear that their
experience of parental depression is reflected in problems with parental
attachment or in increased life events either recently or over the life
span.
Anterior cingulate cortex activation in controls and FH+ participants
The anterior cingulate cortex has cognitive and affective divisions that
are separable both anatomically and
functionally.2
Previous studies in healthy individuals have shown that the affective division
of the anterior cingulate cortex is activated by a number of emotional
manipulations2,23
and our data in healthy participants confirm the findings of Whalen et
al,4 who used
an emotional counting Stroop to demonstrate increased activation in the
pregenual region of the affective subdivision of the anterior cingulate cortex
in response to emotional relative to neutral words. Also, in agreement with
Whalen et al, we found that the emotional counting Stroop task was
associated with an overall deactivation in this subdivision compared with
fixation but that the deactivation was relatively less during presentation of
emotional words. It has been suggested that the overall deactivation of the
affective subdivision of the anterior cingulate cortex in response to the
emotional counting Stroop reflects reciprocal inhibition from the cognitive
subdivision with the purpose of maintaining cognitive performance where there
is increased competition for attentional
resources.2,4
Despite this deactivation, the relative increase in activity of the affective
subdivision following presentation of emotional v. neutral words
demonstrates the continuing ability of the anterior cingulate cortex to
monitor emotional information during the emotional counting Stroop task.
In contrast to these findings in healthy participants, the affective subdivision of the anterior cingulate cortex in FH+ participants showed no difference in activation pattern to emotional v. neutral words. This suggests that in people at increased familial risk of depression the affective subdivision responds less efficiently to the changing emotional valence of incoming stimuli. This difference in activation pattern appeared to be driven partly by the lessened deactivation to neutral words shown by the FH+ participants. This might imply that in people at increased familial risk of depression the affective subdivision of the anterior cingulate cortex reacts to neutral stimuli as if they had an emotional valence. Whether or not this is the case, our findings suggest that in FH+ people the affective subdivision of the anterior cingulate cortex is less efficient in detecting differences in the emotional quality of sensory input.
Changes in anterior cingulate cortex activity in acute depression
Changes in activity of the anterior cingulate cortex have been reported
frequently in imaging studies of patients who are acutely depressed,
particularly hypoactivity in the cognitive subdivision which may correlate
with impaired performance on cognitive
tasks.24,25
Findings in relation to the affective subdivision are more complex. Wagner
et
al26
used a counting (non-emotional) Stroop, in conjunction with fMRI, to study
anterior cingulate cortex activity in patients with depression who were not
receiving medication. They found no difference in either task performance or
activation in the cognitive subdivision relative to controls; however,
patients demonstrated less deactivation in the affective subdivision, a
finding rather similar to our own. Other imaging studies in patients with
acute depression have measured activation patterns in the anterior cingulate
cortex in response to tasks involving the processing of emotional information.
Findings have been variable, with some investigations demonstrating increased
neural responses to negative emotional stimuli, consistent with the emotional
biases associated with acute
depression.27
However, Elliott et
al,28 using an
affective go/no-go task, noted findings similar to our own, namely blunted
neural activation to both positive and negative emotional stimuli in the
affective subdivision of the anterior cingulate cortex.
Implications
Our data indicate that abnormalities in the neural response to emotional
stimuli in the anterior cingulate cortex can exist independently of the
presence of acute depression and appear to be present in those at increased
familial risk of illness. The pregenual region of the affective subdivision of
the anterior cingulate cortex, implicated in our study, has connections to
other brain regions known to be involved in emotional experience and
expression, including the orbitofrontal cortex, amygdala, hippocampus and
ventral
striatum.25,29
In this respect the pregenual affective subdivision of the anterior cingulate
cortex is well placed to play a key role in the integration of emotional and
cognitive
information.2 Hence,
abnormalities in this area could be associated with impaired ability to use
emotional information to influence decision-making, as we observed in an
emotional categorisation task in FH+
participants.1 It is
possible that deficits of this sort could result in difficulties in making
complex social decisions; this may be one mechanism through which increased
familial risk of depression could be
expressed.30
It is important to note that we also observed differential neural activations to the emotional counting Stroop between FH+ and controls in brain regions other than the anterior cingulate cortex, including the thalamus and areas of prefrontal cortex, some of which are known to be associated with emotional processing. Although many of these brain regions have connections to the anterior cingulate cortex, these more widespread changes support the idea of a distributed circuitry underpinning both emotional processing and the risk of clinical mood disorders.31,32 Hence, vulnerability to depression is likely to be associated with changes across a network of areas rather than dysfunction solely in the anterior cingulate cortex. For example, reduced connectivity between thalamus and anterior cingulate cortex has been demonstrated in patients with depression compared with healthy controls.33 Future studies investigating temporal correlations between BOLD response in the anterior cingulate cortex and the prefrontal/limbic regions reported above are warranted to examine whether altered functional integration and/or aberrant connectivity pre-date the onset of depression in at-risk individuals.
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P. Tyrer From the Editor's desk. The British Journal of Psychiatry, September 1, 2009; 195(3): 280 - 280. [Full Text] [PDF] |
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