Multiple Visual Field Representations in the Visual Wulst of a Laterally Eyed Bird, the Zebra Finch (Taeniopygia guttata)

Abstract

The visual wulst is the telencephalic target of the avian thalamofugal visual system. It contains several retinotopically organised representations of the contralateral visual field. We used optical imaging of intrinsic signals, electrophysiological recordings, and retrograde tracing with two fluorescent tracers to evaluate properties of these representations in the zebra finch, a songbird with laterally placed eyes. Our experiments revealed that there is some variability of the neuronal maps between individuals and also concerning the number of detectable maps. It was nonetheless possible to identify three different maps, a posterolateral, a posteromedial, and an anterior one, which were quite constant in their relation to each other. The posterolateral map was in contrast to the two others constantly visible in each successful experiment. The topography of the two other maps was mirrored against that map. Electrophysiological recordings in the anterior and the posterolateral map revealed that all units responded to flashes and to moving bars. Mean directional preferences as well as latencies were different between neurons of the two maps. Tracing experiments confirmed previous reports on the thalamo-wulst connections and showed that the anterior and the posterolateral map receive projections from separate clusters within the thalamic nuclei. Maps are connected to each other by wulst intrinsic projections. Our experiments confirm that the avian visual wulst contains several separate retinotopic maps with both different physiological properties and different thalamo-wulst afferents. This confirms that the functional organization of the visual wulst is very similar to its mammalian equivalent, the visual cortex.

Seeing the Forest for the Trees, and the Ground Below My Beak: Global and Local Processing in the Pigeon’s Visual System

“…The visual Wulst is likely homologous with V1 and displays some similarities in laterally eyed birds. These include orientated edge detectors ( Ng et al, 2010 ), flexible reward and stimulus association coding ( Anderson et al, 2020 ), and retinotopically organized maps of visual space ( Revzin, 1969 ; Gusel’nikov et al, 1977 ; Bischoff et al, 2016 ). There is also evidence that the Wulst is involved in representing global spatial information in comparison with the tectofugal pathway, as opposed to local beacons.…”

Evolution of neural processing for visual perception in vertebrates

“…In addition, they showed that eye alignment as well as binocularity and retinal disparity tuning in the Wulst, depend on early binocular experience, as they do in mammals (Pettigrew & Konishi, ). Subsequent studies show that the Wulst contains several retinotopic areas, each with distinct thalamo‐Wulst inputs and functional properties (Bischof et al, ). In one area, >90% of neurons respond to illusory contours (contours inferred from boundaries of phase‐shifted gratings), as do a subset of neurons in the mammalian V1 (Nieder & Wagner, ).…”

Light-incubation effects on lateralisation of single unit responses in the visual Wulst of domestic chicks

“…Visual Wulst sends projections to various structures including the hippocampal formation and the nido-and mesopallium (Shanahan et al 2013;Atoji et al 2018). The visual Wulst contains many visually responsive neurons (Revzin 1969;Gusel'nikov et al 1977;Ng et al 2010), which are organised according to multiple retinotopic maps (Michael et al 2015;Bischof et al 2016) and are sensitive to motion and orientation akin to those found in the mammalian visual cortex. Visual Wulst also shows column-like organisation (Stacho et al 2020).…”