Distraction modulates anterior cingulate gyrus activations during the cold pressor test.

The anterior cingulate gyrus (ACG) is part of a neural network implicated in attention-demanding tasks, such as the experience of pain. However, the regions within the ACG responding to cognitive demands and to painful stimulation are not identical. Since directing attention away from a painful stimulus is known to reduce the perceived pain intensity, we hypothesized that distraction from pain would result both in decreased activation of ACG subregions responsive to painful stimulation and increased activation of ACG subregions responsive to the distraction task. BOLD fMRI has comparatively high spatial resolution and allows for better identification of ACG subregional responses than other neuroimaging techniques. Twelve subjects were tested using the cold pressor test (CPT), a verbal attention task (VAT), and a distraction task (DT) (a combination of the CPT and VAT). Analysis was performed on a voxel-by-voxel basis using a general linear model as implemented in SPM99. In addition to ACG activations common to both the CPT and VAT, we identified one CPT-specific cluster in an area corresponding to BA24'. The modulation effect of distraction on pain was assessed by contrasting (CPT-DT) and (DT-CPT). In support of our hypothesis, contrast (CPT-DT) revealed a decrease in BA24' during the DT and contrast (DT-CPT) showed increased activation in BA32/32'. These data suggest that distraction from pain and concomitant low pain ratings are reflected in distinct ACG subregional responses.