Electrophysiological characteristics of tectal and thalamo‐cortical divisions of the visual system in lower vertebrates

Abstract

Electrophysiological characteristics of the visual system have been investigated on an ascending phylogenetic scale in submammalian vertebrates. I n cyclostomes and plagiostomes the only system of vision is retino-tectal. In lampreys spread of excitation from visual centers to descending paths of the spinal cord occurs readily, as a manifestation of diffuse, primitive brain. As a result of progressive cephalization, a new retino-thalamo-cortical system arises in amphibia and reptilia. The retino-tectal system, however, retains its leading role. Optic tectum visual potentials are of short latency, displaying stability of pattern and aptitude to reproduce stimulation rhythm, making them comparable to primary responses of the mammalian cortex. The phylogenetically more recent retino-thalaniocortical system has not attained structural or functional maturity. Due to its diffuse organization, visual potentials generated in the surface cortical layer are of long latency, displaying aptitude to fatigue and recruiting on rhythmical stimulation, sensitivity to nembutal; being unlike the primary responses of the mammalian cortex, they should rather be regarded as responses of a non-specific type. Electrical stimulation of dorsal thalamic structures in the frog, turtle and varanus also fails to evoke cortical responses of a primary type. In the course of phylogenetic development, the retino-thalamo-cortical system evidently goes through a stage (amphibia, reptiles), when representation of the function of vision is of a mainly non-specific nature.

The Effects of Telencephalic Lesions on Visually Mediated Prey Orienting Behavior in the Leopard Frog <i>(Rana pipiens)</i>

“…Visual inputs and visual activity are present in the pallium of anurans [Karamian et al, 1966;Vesselkin et al, 1971;Grusser and Grusser-Cornehls, 1976;Finkenstädt et al, 1986;Finkenstädt, 1988Finkenstädt, , 1989, as are possible descending projections to the optic tectum [Neary, 1990;Northcutt and Ronan, 1992]. We have nevertheless found that removal of large portions of the dorsal telencephalon, including virtually all of the pallium, produced no discernible contralateral visual orienting deficit and did not abolish the ability to orient accurately towards prey stimuli in any part of the visual field.…”

“…A unilateral lesion to the visual cortex, a structure that constitutes one component of the pallium in mammals, is known to produce a contralateral orienting deficit in cats [Sprague, 1966;Sherman, 1977;Wallace et al, 1989Wallace et al, , 1990. The pallium of anurans is involved in visual information processing [Karamian et al, 1966;Vesselkin et al, 1971;Grusser and Grusser-Cornehls, 1976;Finkenstädt et al, 1986] and sends efferents to structures that, in turn, project to the optic tectum [Neary, 1990;Northcutt and Ronan, 1992]. Like visual cortex in cats, it may also possess a direct projection to the tectum [Neary, 1990;Northcutt and Ronan, 1992].…”

“…The pallium of anurans, like the isocortex of mammals, is involved in the processing of visual information. Visually elicited activity in the medial pallium of frogs has been reported in evoked potential [Karamian et al, 1966;Vesselkin et al, 1971] and single unit [Grusser and Grusser-Cornehls, 1976] studies. Evidence for pallial activity in response to visual stimuli in toads has also been reported using the 2 deoxyglucose technique [Finkenstädt et al, 1986;Finkenstädt, 1988Finkenstädt, , 1989.…”

Responses of Single Neurons in the Toad’s Caudal Ventral Striatum to Moving Visual Stimuli and Test of Their Efferent Projection by Extracellular Antidromic Stimulation/Recording Techniques

“…Karamian et al [1966] recorded slow-wave potentials in the frog's medial pallium ('primordium hippocampi') evoked by electrical stimulation of the optic nerve or the thalamus. Trepakov [1974] found postsynaptic inhibition in the medial pallium.…”

The Effects of Telencephalic Lesions on Visually Mediated Prey Orienting Behavior in the Leopard Frog <i>(Rana pipiens)</i>

“…Although research on visual processing in amphibians has traditionally focused on the midbrain, there is substantial and increasing evidence that the forebrain also plays an important role: neuroanatomical evidence in frogs [Vesselkin et al, 1971;Halpern, 1972;Northcutt, 1972;Gruberg and Ambros, 1974;Kicliter and Northcutt, 1975;Northcutt and Royce, 1975;Scalia, 1976;Kicliter, 1979;Ronan and Northcutt, 1979;Vesselkin et al, 1980;Wilczynski and Northcutt, 1983a;Neary, 1984] and salamanders [Kokoros and Northcutt, 1977;Himstedt, 1986, 1988]; electrophysiological evidence [Karamian et al, 1966;Vesselkin et al, 1971;Liege and Galand, 1972;Gruberg and Ambros, 1974;Grusser and Grusser-Cornehls, 1976;Finkenstädt et al, 1986;Finkenstädt and Ewert, 1988;Finkenstädt, 1989;Merkel-Harff and Ewert, 1991], and behavioral evidence [Ewert, 1970[Ewert, , 1980Ingle, 1991]. It appears that some form of the 'two visual systems' paradigm probably applies to amphibians as well as to mammals [Ingle, 1973[Ingle, , 1983.…”