Organization of felt and seen pain responses in anterior cingulate cortex.

Previous neuroimaging studies comparing pain observation with directly-experienced pain have shown conjoint activations in the cingulate cortex between felt and seen pain. However, whereas this phenomenon may be due to the functional-anatomical overlap of a shared neural substrate, it may also reflect neighboring but distinct activations for felt and seen pain respectively, the co-localization of which is made more likely in group-averaged, spatially-smoothed data. This study explores responses to felt and seen pain, and their spatial overlap, on unsmoothed data from single subjects. Significant activation for the statistical conjunction of felt and seen pain effects was present both at the group level and in six of the eleven individual subjects. However, although each subject showed distinct felt and seen pain areas in the cingulate, a conjunction between these activations was not found in every individual. Among those that showed a felt-seen pain conjunction, its location along the gyrus was variable and the conjunction always fell in a spatially intermediate location between the felt and seen pain activations. These results suggest that the BOLD signal conjunction originates from the intersection of adjacent and partially distinct activations--which do not necessarily always overlap-- rather than from a single neural population coding equally for felt and seen pain. This has implications for the interpretation of BOLD data in addressing "mirrorlike" activations in general, whether in action-related or pain-related areas.