Cortical Evoked Potentials Recorded from the Guinea Pig Without Averaging

Abstract

Potentials evoked by tonal pulses and recorded with a monopolar electrode on the pial surface over the auditory cortex of the guinea pig are presented. These potentials are compared with averaged potentials recorded in previous studies with an electrode on the dura. The potentials recorded by these two techniques have similar waveforms, peak latencies and thresholds. They appear to be generated within the same region of the cerebral cortex. As can be expected, the amplitude of the evoked potentials recorded from the pial surface is larger than that recorded from the dura. Consequently, averaging is not needed to extract the evoked potential once the dura is removed. The thresholds for the evoked cortical potential are similar to behavioral thresholds for the guinea pig at high frequencies; however, evoked potential thresholds are elevated over behavioral thresholds at low frequencies. The removal of the dura and the direct recording of the evoked potential appears most appropriate for acute experiments. The recording of an evoked potential with dura electrodes employing averaging procedures appears most appropriate for chronic studies.

The data presented in this article were collected in partial fulfillment of the requirements for the doctoral degree in the Department of Medical Psychology, University of Oregon Medical School. The work was in part sponsored by Program Project no. NS 09889.