Paroxysmal visual evoked potentials (PVEPs) in Papio papio. I. Morphological and topographical characteristics. Comparison with paroxysmal discharges

Abstract

This study describes a method of stimulation capable of inducing fronto-rolandic (FR) visual evoked potentials of very large amplitude (up to an even greater than 1000 μV) to isolated flashes in the naturally photosensitive Papio papio and in those made photosensitive by an injection of allylglycine. The morphological and topographical characteristics of these FR paroxysmal visual evoked potentials (PVEPs) are described in two experimental situations: the animals either awake and placed in a restraining chair, or paralysed with a synthetuc curare agent and ventilated artificially. During thes study, the following observations were made: 1. (1) The morphology of the PVEPs is similar to that of the paroxysmal discharges (PD) induced by intermittent light stimulation (ILS) in photosensitive animals. 2. (2) The PVEPs are observed in the FR cortex; those of maximal amplitude are located in the precentral area. Simultaneously, the specific occipital responses retain their usual characteristics and never become paroxysmal. 3. (3) PVEPs have never been observed in non-photosensitive animals in the absence of allyglycine. In non-paralysed photosensitive or allyglycine-injected animals the PVEPs are hard to obtain, while the PDs and seizures on the contrary are easily induced by the ILS. Conversely, in paralysed and allyglycine-injected animals, the PDs and seizures are difficult to obtain whereas the PVEPs occur with increased amplitude and frequency. Several questions arise from these observations concerning the origin of the visual afferents to the FR cortex which induce the PVEPs, and concerning the possible relationships between the PVEPs and the PDs induced by ILS. In response to the latter question, it seems that despite the similarities of morphological and topographical characteristics, the PVEPs and PDs evolve differently after curaruzation of the animal.