Unmasking of presynaptic and postsynaptic high-frequency oscillations in epidural cervical somatosensory evoked potentials during voluntary movement.
OBJECTIVE
To investigate the effect of the voluntary movement on the amplitude of the somatosensory evoked potentials (SEPs) recorded by an epidural electrode at level of the cervical spinal cord (CSC).


METHODS
Fourteen patients underwent an epidural electrode implant at CSC level for pain relief. After the median nerve stimulation, SEPs were recorded from the epidural electrode and from 4 surface electrodes (in frontal and parietal regions contralateral to the stimulated side, over the 6th cervical vertebra, and on the Erb's point). SEPs were recorded at rest and during a voluntary flexo-extension movement of the stimulated wrist. Beyond the low-frequency SEPs, also the high-frequency oscillations (HFOs) were analysed.


RESULTS
The epidural electrode contacts recorded a triphasic potential (P1-N1-P2), whose negative peak showed the same latency as the cervical N13 response. The epidural potential amplitude was significantly decreased during the voluntary movement, as compared to the rest. Two main HFOs were identifiable: (1) the 1200 Hz HFO which was significantly lower in amplitude during movement than at rest, and (2) the 500 Hz HFO which was not modified by the voluntary movement.


CONCLUSIONS
The low-frequency cervical SEP component is subtended by HFOs probably generated by: (1) postsynaptic potentials in the dorsal horn neurones (1200 Hz), and (2) presynaptic ascending somatosensory inputs (500 Hz).


CONCLUSIONS
Our findings show that the voluntary movement may affect the somatosensory input processing also at CSC level.
Unità Operativa di Neurofisiopatologia, CTO, Via S. Nemesio 21, 00145 Rome, Italy.
Angelo
A
Insola
Luca
L
Padua
Paolo
P
Mazzone
Massimiliano
M
Valeriani
D000328:Adult; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D004567:Electrodes, Implanted; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology; D008875:Middle Aged; D009068:Movement / Q000502:physiology* / Q000528:radiation effects; D010146:Pain / Q000503:physiopathology; D059408:Pain Management; D011930:Reaction Time / Q000502:physiology; D012146:Rest / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology* / Q000528:radiation effects; D014057:Tomography, X-Ray Computed / Q000379:methods