Assessment of cortical reorganization and preserved function in phantom limb pain: a methodological perspective

TL;DR

This study investigates cortical reorganization in phantom limb pain using fMRI during a virtual hand motor task, revealing distinct neural activity patterns in S1 and M1 that relate variably to pain intensity.

Contribution

It highlights methodological differences in assessing cortical representations and clarifies the relationship between neural activity and phantom limb pain.

Findings

Amputees show increased M1 and S1 activity compared to controls.

Neural activity correlates with pain only when using group-defined ROIs.

Different analysis approaches reveal distinct pain-related processes.

Abstract

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.