Cortical processing of brush-evoked allodynia.

The cortical processing of allodynia (touch-evoked pain) resulting from neuralgia of the lateral cutaneous femoral nerve was investigated with a newly designed pneumatically driven brush by means of magnetoencephalography. Brushing the unaffected thigh produced subsequent activation of the contralateral primary somatosensory cortex (S1) with peak latencies of 37 and 56 ms. Brushing the affected side led to comparable activation of the contralateral S1 cortex. In addition, the magnetic fields were stronger, and the corresponding equivalent current dipoles were located more laterally, consistent with the presence of cortical reorganisation. Allodynia was also accompanied by an activation of the cingulate cortex, occurring only 92 ms. after stimulus onset, an observation suggesting an Abeta-fiber-mediated neuronal pathway involved in dynamic mechanical allodynia. This study corroborates the concept of cortical reorganisation underlying chronic pain. Furthermore, it demonstrates that a remarkable early activation of the cingulate cortex may be involved in the cortical processing of allodynia.