Responses at cerebral somatosensory I and peripheral nerve evoked by graded electrocutaneous stimulation

¹ West Haven Veterans Administration Hospital and Yale University School of Medicine, New Haven, Connecticut

Evoked potentials were recorded with macroelectrodes from peripheral nerve and cerebral somatosensory I of anesthetized cats following graded electrocutaneous stimulation. The sizes of the peripheral and cortical responses increased according to multiple-limbed functions as stimulus intensity grew. Each negatively accelerated limb of the cortical function began and reached asymptote at the same intensities as did the companion limb of the nerve function. The cortical response grew less rapidly than the response of nerve at high intensities and more rapidly at low intensities. Within each limb of the nerve function, however, the cortical response linearly followed the nerve response. Cortical potentials evoked by stimulation of a fixed cutaneous locus displayed lower thresholds and higher amplitudes in the central region than out towards the perimeter of the cortical representation of that locus. The high-threshold responses did not reverse polarity upon intracortical recording, did not potentiate upon application of strychnine or Metrazol, and disappeared following ablation of the central part of the representation which yielded potentiated responses upon strychninization. The high-threshold responses thus seem due to volume conduction.