[The value of differential recording of subcortical somatosensory evoked potentials (SEP) in neurosurgery].

The role of subcortical median nerve somatosensory evoked potential (SEP) testing is exemplified in neurosurgical patients with syringomyelia, coma, brain death, or undergoing intraoperative monitoring. Of special importance is the isolated recording of two components with similar latencies but different generator sites: N13 (lower cervical spinal cord) and P14 (caudal brain stem). These two potentials overlap in conventional neck-scalp recordings using a frontal reference. Theoretical implications and practical aspects of a differential recording of subcortical SEP in neurosurgery are discussed.