Spinal cord evoked potential

Spinal cord evoked potentials (SCEPs) used as a technique for intraoperative neurophysiological monitoring can be divided into several groups depending on the stimulation method. SCEP evoked by direct motor cortex stimulation enables the recording of the descending volley passing through the corticospinal tract. Such potentials are termed D (direct)- and I (indirect)-waves. D-wave reflects the function of the corticospinal tract directly and is regarded as an appropriate parameter for the intraoperative monitoring of motor function. On the other hand, the corticospinal tract may be activated by transcranial stimulation and a potential similar to D-wave can be recorded from the spinal epidural space. Previous studies, however, indicated that the site of transcranial stimulation is around the lower level of the brainstem and the response includes the potentials coming from other neural tracts. In addition, the responses of SCEPs evoked by spinal cord and peripheral nerve stimulations are generally considered to reflect mainly the function of the deep sensory pathway. Therefore, SCEPs evoked by transcranial, spinal cord and peripheral nerve stimulations cannot be used as a parameter to monitor motor function directly. It is particularly important to know the characteristics of each SCEP and apply each potential to the most appropriate situation.