Synaptic and non-synaptic components of the human cervical evoked response.

The human cervical evoked response comprises a main negative wave and a following positivity. The peak of the negative wave, N13, is preceded by a small notch, N11, on the ascending negativity and is followed by another notch, N14, on the descending negative slope. The mechanisms of the components in the human cervical evoked response are still subject to discussion. In the present study conventional neurophysiological techniques were applied to see whether the components were of synaptic or non-synaptic origin. Resistance to high-frequency stimulation, refractoriness as tested by train or double shock conditioning stimuli and the effect of graded stimulation revealed that N11 and N14 fulfilled the criteria of a non-synaptic origin. N13 and the positive wave had properties pointing to a synaptic origin, the latter evidently reflecting an inhibitory mechanism. Each component in the human cervical evoked response both morphologically and functionally resembled the well known subcomponents in the spinal cord dorsum potential in experimental animals.