  Phantom limb pain (PLP) has been associated with both the reorganization of
the somatotopic map in primary somatosensory cortex (S1) and preserved S1
function. Here we assessed the nature of the information (sensory, motor) that
reaches S1 and methodological differences in the assessment of cortical
representations that might explain these findings. We used functional magnetic
resonance imaging during a virtual hand motor task, analogous to the classical
mirror box task, in amputees with and without PLP and in matched controls. We
assessed the relationship between task-related activation maxima and PLP
intensity in S1 versus motor (M1) maps. We also measured cortical distances
between the location of activation maxima using region of interest (ROI),
defined from individual or group analyses. Amputees showed significantly
increased activity in M1 and S1 compared to controls, which was not
significantly related to PLP intensity. The location of activation maxima
differed between groups depending on M1 and S1 maps. Neural activity was
positively related to PLP only in amputees with pain and only if a
group-defined ROI was chosen. These findings show that the analysis of changes
in S1 versus M1 yields different results, possibly indicating different
pain-related processes.
