Origin of the initial negative potential (N15) recorded on the skull by superficial radial nerve stimulation in the cat.

The origin of the initial prominent negative potential with a latency of about 15 msec (N15), recorded on the skull by superficial radial nerve stimulation was studied in the cat, and the following results were obtained. In the direct recording from the cortex, SEPs were elicited from the SI and SII areas, as well as the lateral gyrus and anterior suprasylvian gyrus. Among various wave forms recognized in the SI area, diphasic positive-negative (P-N) potential obtained from the postero-lateral part was most distinct, representing the primary evoked potential. Responses recorded on the dura and those directly on the cortex showed similar wave patterns over many sites. Although different forms of evoked potentials were recorded extensively over the skull, the most prominent negative potential was elicited at the site corresponding to the postero-lateral part of the SI area. The latency of this potential was approximately in agreement with that of the negative component of the P-N potential recorded on the cortex. Based on the intracortical laminar analysis of P-N potential, the positive component of this potential was assumed to reflect the activity of cells in the deeper layer of the cortex. The negative component, on the other hand, might represent activities of apical dendrites of the cortex. From the result of functional elimination of the cortex, however, this positive component was thought to contain potentials from far field neural structures. N15 recorded on the skull completely disappeared during cortical spreading depression.(ABSTRACT TRUNCATED AT 250 WORDS)