Smoking reduces conflict-related anterior cingulate activity in abstinent cigarette smokers performing a Stroop task

Abstract

Prior research suggests that abrupt initiation of abstinence from cigarette smoking reduces neural cognitive efficiency. When cognitive efficiency is high, processing speed and accuracy are maximized with minimal allocation of cognitive resources. The study presented here tested the effects of resumption of smoking on cognitive response conflict after overnight abstinence from smoking, hypothesizing that smoking would enhance cognitive efficiency. Twenty paid research volunteers who were chronic cigarette smokers abstained from smoking overnight (>12 h) before undergoing fMRI while performing a color-word Stroop task during two separate test sessions: one that did not include smoking before testing and another one that did. Statistical analyses were performed by modeling the Stroop effect (incongruent >congruent) BOLD response within a collection of a priori regions of interest that have consistently been associated with cognitive control. Behavioral assessment alone did not reveal any significant differences in the Stroop effect between the two sessions. BOLD activations, however, indicated that in the right anterior cingulate cortex (ACC), smokers had significantly less task-related activity following smoking (p<0.02). In contrast, the right middle frontal gyrus exhibited significantly greater activity after smoking as compared to the no-smoking session (p<0.003). Exaggerated neural activity in the ACC during nicotine withdrawal may reflect a compensatory mechanism by which cognitive control networks expend excessive energy to support selective attention processes. Resumption of smoking may enhance cognitive control in smokers, involving a reduction in ACC response conflict activity together with improvement in conflict resolution involving the dorsolateral prefrontal cortex.

Figure 1

For the no-smoking and smoking sessions showing: (a) Mean Stroop errors (^*p<0.05 incongruent>congruent); (b) Stroop reaction time (^***p<0.001 incongruent>congruent; ^**p<0.01 non-smoking>smoking); and (c) mean Stroop effect.

Figure 2

Showing average BOLD activation across the whole brain for the Stroop effect in (a) the no-smoking session and (b) the smoking session. Z (Gaussianized T/F) statistic images were thresholded using clusters determined by Z=2.3 and corrected cluster significance level of p=0.05. The scale represents the color (from dark to light yellow) of the cluster corresponding to the increasing Z-statistic. The structural image represents the MNI152 average normal brain with corresponding horizontal coordinates (inferior-superior).

Figure 3

Small-volume correction analysis showing (a) voxel cluster of activity across both the left and right ACC, and (b) the local maxima of activity, located in the right ACC (x=4, y=22, z=32), where smokers showed a significantly greater BOLD response during the no-smoking as compared with the smoking session for the incongruent>congruent contrast (p<0.02, paired t-test). The scale represents the color (from dark to light yellow) of the cluster corresponding to the increasing Z-statistic. The structural image represents the MNI152 average normal brain with corresponding coronal (anterior-posterior) and sagittal (right-left) coordinates.

Figure 4

Small-volume correction analysis showing the (a) coronal section and (b) sagittal section voxel cluster of activity located in the right MFG (x=48, y=24, z=28), where smokers showed a significantly greater BOLD response during the smoking as compared with the no-smoking session for the incongruent>congruent contrast (p<0.003, paired t-test). The scale represents the color (from dark to light yellow) of the cluster corresponding to the increasing Z-statistic. The structural image represents the MNI152 average normal brain with corresponding coronal (anterior-posterior) and sagittal (right-left) coordinates.