Goal-directed behavior requires cognitive control to regulate neural processing when conflict is encountered. The dorsal anterior cingulate cortex (dACC) has been associated with detecting response conflict during conflict tasks. However, recent findings have indicated not only that two distinct subregions of dACC are involved in conflict processing but also that the conflict occurs at both perceptual and response levels. We clarified a functional dissociation of the caudal dACC (cdACC) and the rostral dACC (rdACC) in responding to different sources of conflict. The cdACC was selectively engaged in perceptual conflict whereas the rdACC was more active in response conflict. Further, the dorsolateral prefrontal cortex (DLPFC) was coactivated not with cdACC but with rdACC. We suggest that cdACC plays an important role in regulative processing of perceptual conflict whereas rdACC is involved in detecting response conflict

Chobok Kim

James Kroger

Jeounghoon Kim

English

Nature Precedings

1 
A functional dissociation of conflict processing within 
anterior cingulate cortex 
 
Chobok Kim1, James K. Kroger1,2, and Jeounghoon Kim3 
 
1Department of Psychology, New Mexico State University, NM, USA, 2The Mind 
Research Network, Albuquerque, NM, USA, 3School of Humanities & Social Sciences, 
KAIST, Daejeon, Korea 
2 
Goal-directed behavior requires cognitive control to regulate neural processing 
when conflict is encountered. The dorsal anterior cingulate cortex (dACC) has 
been associated with detecting response conflict during conflict tasks. However, 
recent findings have indicated not only that two distinct subregions of dACC are 
involved in conflict processing but also that the conflict occurs at both perceptual 
and response levels. We clarified a functional dissociation of the caudal dACC 
(cdACC) and the rostral dACC (rdACC) in responding to different sources of 
conflict. The cdACC was selectively engaged in perceptual conflict whereas the 
rdACC was more active in response conflict. Further, the dorsolateral prefrontal 
cortex (DLPFC) was coactivated not with cdACC but with rdACC. We suggest 
that cdACC plays an important role in regulative processing of perceptual conflict 
whereas rdACC is involved in detecting response conflict.  
 
Goal-directed behavior often requires humans to overcome interference caused by 
distraction. The Stroop task1 is one of the most frequently employed paradigms for 
studying human ability to control cognition in the face of interference. Subjects are 
asked to name the color of colored words. Response time (RT) is increased in naming 
the ink color of an incongruent stimulus (e.g., “RED” printed in blue ink) compared to a 
neutral stimulus (e.g., “XXXX” printed in blue ink). This is referred to as the Stroop 
interference effect. The conflict monitoring theory suggests that the dorsal anterior 
cingulate cortex (dACC) plays a role in detecting conflict in tasks such as the Stroop 
task and the flanker task2, and the dorsolateral prefrontal cortex (DLPFC) engages in 
resolving the conflict3-6. An important aspect of this theory is that the conflict is caused 
at the response level.  
In recent years, however, increasing numbers of neuroimaging studies have 
suggested that cortical responses to conflict depend on the source of conflict 7. 
3 
Specifically, it has been suggested that rostral dACC (rdACC) recruitment is restricted 
to the response conflict whereas caudal dACC (cdACC) is involved in pre-response 
conflict8-10. A neuropsychological study of patients with legions in cdACC or rdACC 
has supported this dissociation11. Other neuroimaging studies12-15 and a recent review16 
found that two distinct regions within rostral and caudal dACC are involved in conflict 
processing but that the functions of the two subregions were not differentiated. We 
localized the coordinates of dACC activations reported in the previous studies and 
identified two distinctive subregions of dACC, which correspond to posterior rostral 
cingulate zone and anterior rostral cingulate zone17 (Figure 1). 
We assumed that rdACC and cdACC are involved in the conflict tasks and 
dissociated by the source of conflict: perceptual conflict recruits cdACC whereas 
response conflict recruits rdACC. We employed a version of the Stroop matching task 
used in a previous behavioral study18 that allowed measurement of perceptual conflict 
and response conflict separately. Experimental tasks were composed of two conditions, 
a color-response condition (CR) and a word-response condition (WR), in which each 
condition included incongruent and neutral trials. Thus four types of trials were 
included; incongruent CR (iCR), neutral CR (nCR), incongruent WR (iWR) and neutral 
WR (nWR). Response conflict was minimized in iCR as subjects were only required to 
identify the sample color by selecting the corresponding color from two color cues and 
thus the interference effect was assumed to be caused by perceptual conflict at the pre-
response level. In contrast, response conflict was maximized in iWR in which subjects 
were to translate the ink color of the colored word stimulus into a verbal representation, 
inhibiting the prepotent processing. Thus, the interference effect in WR was caused by 
both perceptual and response conflict.  
Behavioral performance on the tasks showed that hit rates of each subject were 
higher than 96% in all conditions. RT was analyzed using a two-way repeated-measure 
4 
ANOVA (Figure 2). The results showed significant main effects of both conflict 
(F(1,12)= 43.222, MSe=.013, p=.000) and response modality (F(1,12)= 38.747, MSe=.059, 
p=.000), as well as a significant interaction effect (F(1,12)= 18.086, MSe=.005, p=.001). 
The interference effect was greater in WR (284 ms) than in CR (125 ms). Since the 
response cues of iWR induced response conflict but the sample of iWR also included 
perceptual conflict, we calculated the response interference effect (i.e., 159 ms) by 
subtracting nWR from iWR in each subject. There was no significant difference 
between the sizes of the two interference effects (t(12)=.933, p=.369) nor a significant 
correlation between them (r=.285, p=.345). These results do indicate, however, that the 
Stroop interference effect is caused by both perceptual and response conflicts18,19. 
For fMRI data, we compared incongruent trials with neutral trials for CR and WR 
separately (Figure 3a and Supplementary Table 1). The results showed that when 
subjects performed CR, cdACC activity (peaked at y=16) was greater on iCR than on 
nCR. In contrast, both cdACC and rdACC (peaked at y=16 and at y=33, respectively) 
showed greater activity on iWR than on nWR. However, the comparison of iCR with 
nCR includes only perceptual conflict, whereas the comparison of iWR with nWR 
includes both perceptual and response conflicts. Thus we analyzed the same data using a 
two-way ANOVA using factors of the conflict (incongruent vs.neutral) and the response 
modality (WR vs. CR) in order to measure perceptual conflict and response conflict 
separately (see Figure 3b and Supplementary Table 2). We found a positive main effect 
of the conflict in cdACC (peaked at y=5). In contrast, an interaction effect (i.e., [iWR – 
nWR] – [iCR – nCR]) was significant in rdACC (peaked at y=27). The main effect of 
response modality (i.e., [WR – CR]) was not significant in any subregion of ACC. We 
depicted BOLD signal changes of each trial type in the ROIs within both cdACC and 
rdACC in figure 4. In comparisons of peak activation between iCR and nCR and 
between iWR and nWR using paired-sample t-tests (two-tailed), the cdACC activation 
was higher in iCR than in nCR (t(12)=2.360, p=.036) and in iWR than in nWR 
5 
(t(12)=3.303, p=.006). In contrast, in the rdACC region, the peak activation was higher in 
iWR than in nWR (t(12)=2.963, p=.012), whereas iCR and nCR were not different 
(t(12)=.442, p=.666).  
To test the relationship between neural activity (i.e., the conflict effect) and 
behavioral responses (i.e., the interference effect), we calculated conflict effects of each 
subject using the peak value of the BOLD signal changes (i.e., iWR - nWR for the 
response conflict and iCR - nCR for the perceptual conflict) in both cdACC and rdACC. 
The results showed that the positive correlation between the interference effect observed 
in CR and the perceptual conflict effect was significant in cdACC (r=.623, p=.023) but 
not in rdACC (r=.402, p=.173). In contrast, the interference effect in WR and the 
response conflict effect showed a significant positive relationship in rdACC (r=.740, 
p=.004) but not in cdACC (r=.508, p=.076). The estimated response interference effect 
was highly correlated with rdACC activity (r=.748, p=.003) but not with cdACC 
activity (r=.424, p=.148).  
An additional important finding was observed in DLPFC (see Supplementary 
Table 1; Brodmann area (BA) 9; Talairach coordinates: 48, 13, 27). The comparison of 
the incongruent condition with the neutral condition showed enhanced neural activity of 
DLPFC in WR but not in CR. In other words, DLPFC was coactivated with rdACC but 
not with cdACC. The coactivation of DLPFC and rdACC was also observed in the two-
way ANOVA as the positive interaction effect which reflects response conflict (see 
Supplementary Table 2; BA 46; -42 19 21). DLPFC activation in the main effect of 
conflict was mainly caused by iWR since no activation of DLPFC was observed in 
comparison of iCR with nCR. fMRI results showed a functional dissociation of the 
conflict processing within dACC, in which response conflict recruits rdACC whereas 
perceptual conflict involves cdACC in accordance with previous studies8-10,15. The 
coordinates within each subregion of dACC are similar to the mean coordinates of the 
6 
previous studies (see Figure 1). Our ROI analyses confirmed this dissociation, in which 
response conflict results in greater activation in rdACC. In addition, the level of cdACC 
activation was highly related to the interference effect caused by perceptual conflict but 
not by response conflict. According to these findings, it is reasonable to expect that 
error processing is specific only to rdACC. Studies have supported this expectation, 
finding that cdACC was specific to the conflict but not to error processing, while 
rdACC showed error-related activation10,20. 
Cortical response to conflict processing has been observed in rdACC8,9,21,22 while 
others found it in cdACC5,6,23. One possible interpretation of this disagreement is that 
those studies did not separate response-specific conflict from perceptual conflict and 
thus the cdACC activation in their studies might represent an accumulated effect of two 
types of conflict. Another potential interpretation is that the studies employed a 
predefined ROI within cdACC24 or that a large region across dACC was activated by 
both pre-response and response25.  
Another important finding was also found in DLPFC (BA 9/46), which was 
coactivated with dACC only when response conflict occurred. This supports previous 
studies in which DLPFC plays an important role in cognitive control by resolving 
prepotent responses5,21. Even though the interference effect was observed and the 
perceptual conflict activated cdACC, no activation was observed in DLPFC when no 
response conflict occurred. These results suggest that DLPFC is involved in resolving 
only response conflict. However, previous studies reported coactivation of DLPFC, in 
which they found cdACC activation to pre-response conflict such as semantic conflict8 
and target detection10. One possible interpretation of this disagreement is that the task 
conditions of those studies might have required additional top-down processing from 
DLPFC such as a change of response selection strategy26. 
7 
Taken together, we suggest that distinct subregions of dACC are involved in 
conflict processing: cdACC is engaged in perceptual conflict and rdACC is involved in 
response conflict. DLPFC seems specifically recruited only for response conflict, which 
indicates that only response conflict requires top-down cognitive control processing in 
order to override prepotent responses. These results support the conflict monitoring 
theory3, but it might be possible to add a perceptual conflict module to the current 
conflict monitoring theory as a mediator. However, it is unclear how the brain resolves 
the perceptual conflict that occurred in the present study. One plausible suggestion is 
that cdACC plays a role in regulative processing at a perceptual level even if no 
response conflict occurs27. This regulative model would present more general account in 
the conflict monitoring system. 
 
 
8 
METHODS SUMMARY 
Thirteen neurologically healthy right-handed volunteers (ages 19 - 32; five females) 
without color blindness participated in this study. We used a variation of the Stroop 
color-word task in which a sample and a set of two alternative cues were presented in a 
screen. All words in the samples and response cues were presented in Korean. 
Experimental conditions were composed of four types of conditions; iCR, nCR, iWR 
and nWR. The iCR and nCR included two colored rectangles as response cues whereas 
in iWR and nWR the response cues were two color names in words. The task required 
subjects to match the color of the sample with a corresponding response cue. All 
experimental stimuli and null events continued for 2 sec and inter-stimulus-intervals 
averaging 2.9-second followed. All trial types were replicated 48 times in randomized 
order. 
Images were acquired with a 3-T MRI system (Oxford magnet, Varian console 
magnet built by ISOL, fMRI center at KAIST in Daejeon, Korea). T2*-weighted 
gradient echo planner images (EPI) with 20 interleaved slices were acquired for the 
functional images (TR=2sec, TE=35ms, FA=85°, matrix=64X64, in-plane 
resolution=3.44mm, thickness=5mm) which were composed of 2 runs (294 volumes per 
run). T1-weighted images were also obtained.  
SPM5 was used for image preprocessing and statistical analyses. Temporal and 
spatial disparities between slices were corrected and then the images were normalized to 
a standard MNI-305 T1-weighted image and accordingly resampled by isotropic 3mm 
voxels. The images were then spatially smoothed with an 8mm FWHM Gaussian 
kernel. Each condition was included in constructing a general linear model using a 
canonical hemodynamic response function. Contrast images were constructed by 
comparison of experimental events with null events. The contrast images were 
9 
submitted to group-level random-effects analyses (thresholded at p<.05 corrected using 
the false discovery rate28). Paired-sample t-tests and a two-way ANOVA were used.  
10 
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Acknowledgements: We thank Chong Wook Chung for his help in running the experiment and collecting 
the data. This work was supported by Korea BrainTech 21 Research Fund. 
The authors declare they have no competing financial interests.  
Correspondence and requests for materials should be addressed to J. K. (miru@kaist.ac.kr). 
11 
Figure 1. Localization of dACC activations during the Stroop or Stroop-like tasks 
found in selected studies. The white circles are located within rdACC and the 
gray circles are located in cdACC. Two triangles indicate the average 
coordinates of the white circles and of the gray circles. Each location indicates 
Talairach coordinates29 showing the highest peak value in each study. The 
numbers indicate references; 19, 28, 310, 415, 525, 616, 712, 813, 930, 1014. Four of 
these studies (references 1-4) found both cdACC activity sensitive to pre-
response conflict and rdACC activity sensitive to response conflict, one study 
(reference 5) found cdACC activity sensitive to both pre-response conflict and 
response conflict, and others (references 6-10) found two subregions within 
dACC sensitive to conflict processing with no functional dissociation. The 
average coordinates of white circles are x, y, z = 2, 26, 31, and those of gray 
circles are x, y, z = 1, 10, 42. 
 
Figure 2. Behavioral performance on the Stroop tasks. Each bar represents the 
mean of RTs in each condition. Error bars indicate the mean ± the standard 
error of the mean (s.e.m.) 
 
Figure 3. Significant activation within dACC. (A) The conflict effect observed in 
only cdACC (red) for CR but in both cdACC and rdACC (yellow) for WR. (B) 
The main effect of conflict (incongruent vs. neutral) showed significant activation 
in cdACC (red). A positive interaction effect ([iWR - nWR] - [iCR - nCR]) was 
significant in rdACC (yellow).  
 
12 
Figure 4. BOLD signal changes of each trial type with cdACC (the left) and 
rdACC (the right). Error bars indicate mean ± s.e.m. 
 






Co-planar stereotaxic atlas of the human brain.

A functional dissociation of conflict processing within anterior cingulate cortex

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A functional dissociation of conflict processing within anterior cingulate cortex

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