Amplitude reduction of the epidural cervical SEPs during voluntary movement

Fourteen patients, suffering from chronic pain resistant to pharmacological treatment, underwent epidural electrode implant on the cervical spinal cord (CSC) for neuromodulation. After the median nerve stimulation, somatosensory evoked potentials (SEPs) were recorded from the epidural electrode contacts, from the frontal and the parietal regions contralateral to the stimulated side, from an electrode placed over the sixth cervical vertebra and from the Erb's point. SEPs were recorded at rest and during a voluntary flexion-extension movement of the stimulated wrist. The epidural electrode contacts recorded a triphasic potential (P1-N1-P2). The epidural potential amplitude was significantly decreased during voluntary movement compared with the rest, thus suggesting that the effect of movement on SEPs occurs also at CSC level.