Evoked cerebral cortical activity from small peripheral nerve fibers in cat

Abstract

In 19 cats anesthetized with 75% nitrous oxide/25% oxygen, two types of cortical activity have been demonstrated to respond to repetitive stimulation of small myelinated and unmyelinated peripheral nerve fibers. One is a rhythmic 3–4 c/sec high voltage activity seen most prominently in the cortical association areas. The other is a 20–40 c/sec small amplitude train of brief discharges appearing most prominently in the primary somatosensory area. This latter response is related to the activity of smaller peripheral nerve fibers. The two responses differ in that the 20–40 c/sec activity is not evoked by epinephrine, appears shortly after the stimulus, and has a shorter duration of activity than the higher voltage 3–4 c/sec theta activity. The slow rhythm is evoked by epinephrine, is delayed in onset and outlasts an evoking stimulus train. Neither response is evoked by optic stimulation or by stimulation of the larger peripheral afferent fibers. Both varieties of cortical activity are suppressed by intravenous phenobarbital.