Retinal afferents to the tectum opticum and the nucleus opticus principalis thalami in the pigeon

Abstract

The retinal afferents of the tectum opticum and the n. opticus principalis thalami (OPT) were studied with fluorescent tracers in pigeons. Injections into the tectum opticum revealed topographically related areas of high density labelling in the contralateral retina. In these areas up to 15,000 cells/mm2 were labelled. After tectal injections the soma sizes of labelled retinal ganglion cells in the area centralis ranged from 5 to 23 microns with a mean of 7.5 microns. Afferents from the ipsilateral retina could not be demonstrated. Injections into the OPT labelled neurons throughout the retina without a clear topographical relation to the locus of injection. The density never exceeded 150 cells per mm2. The soma size range was 8 to 35 microns with a mean of 14.6 microns. Independently of the injection area within the OPT, the red field in the dorsotemporal retina was always extremely sparsely labelled. The number of labelled ganglion cells in this area never exceeded 25 neurons/mm2. After OPT injections the average density of labelling per unit area was six times higher in the yellow than in the red field. The results confirm previous reports of a massive and topographically organized retinal projection onto the optic tectum. The projection onto the OPT was clearly smaller and with the retrograde tracing techniques in use, an orderly topography has not been demonstrated. The paucity of red field projections onto the OPT suggests that the role of the thalamofugal pathway in binocular integration is very limited.

Functional MRI and functional connectivity of the visual system of awake pigeons

“…This light source was also reflected within the dark gray and was visible to the lateral visual field of the animals with a drastically reduced luminance. It is known that the frontal visual field of pigeons is primarily represented in the tectofugal and less in the thalamofugal system [52,53]. Consequently, lesions of tecto-or thalamofugal structures primarily cause deficits in the frontal and the lateral visual field, respectively [54,55]).…”

Dominant Vertical Orientation Processing without Clustered Maps: Early Visual Brain Dynamics Imaged with Voltage-Sensitive Dye in the Pigeon Visual Wulst

“…This attribute alters the qualitative nature of input into the early visual forebrain. The pigeon visual Wulst receives mainly monocular information as a result of its laterally placed eyes and reduced representation of the frontal binocular field within its thalamofugal system (Remy and Güntürkün, 1991;Güntürkün and Hahmann, 1999) and its receptive fields seldom lay within the binocular visual field (Miceli et al, 1979). The owl's frontally placed eyes provide greater binocular overlap (ϳ44°) (Martin, 1984) and thus owls possess a larger proportion of visual Wulst neurons with binocular receptive fields (Pettigrew, 1979).…”

“…The physiological function of the pigeon visual Wulst is often extrapolated from the knowledge of the owl visual Wulst. However, this practice is not straightforward because these two structures process information that is qualitatively different, the pigeon receiving mainly monocular input from the lateral visual field, compared with the owl's dominant binocular vision (Remy and Güntürkün, 1991;Güntürkün and Hahmann, 1999).…”

Asymmetrical Modes of Visual Bottom-Up and Top-Down Integration in the Thalamic Nucleus Rotundus of Pigeons

“…Indeed, pigeons that were trained to respond quickly to simple stimuli were more adept using the left eye than the right (DiStefano et al, 1987). Because the stimuli in the study by DiStefano et al (1987) were presented in the pigeon's frontal binocular field, which is mainly represented in the tectofugal system (Remy and Güntürkün, 1991;Güntürkün and Hahmann, 1999;Budzynski et al, 2002), the shorter latencies of right rotundal bottom-up cells might indeed guide faster visuomotor responses to simple stimuli.…”