Median nerve somatosensory evoked potentials: recording with cephalic and noncephalic references

We performed both cephalic and noncephalic reference SEP recordings with median nerve stimulation in normals and compared the results obtained from both recordings. Median nerve SEP with non cephalic reference revealed four positive and three negative potentials on scalp, while median nerve SEP with cephalic reference showed only one negative potential on scalp. We conclude that potentials originated from subcortical regions can be recorded from scalp by using noncephalic reference, which is not possible by cephalic reference and potential N20 obtained from somatosensory cortex by using cephalic reference does not present a single potential, consisting of combination of a few potentials. To differentiate these potentials, noncephalic reference must be used.