Optical Imaging of Retinotopic Maps in a Small Songbird, the Zebra Finch

Abstract

BackgroundThe primary visual cortex of mammals is characterised by a retinotopic representation of the visual field. It has therefore been speculated that the visual wulst, the avian homologue of the visual cortex, also contains such a retinotopic map. We examined this for the first time by optical imaging of intrinsic signals in zebra finches, a small songbird with laterally placed eyes. In addition to the visual wulst, we visualised the retinotopic map of the optic tectum which is homologue to the superior colliculus in mammals.Methodology/Principal FindingsFor the optic tectum, our results confirmed previous accounts of topography based on anatomical studies and conventional electrophysiology. Within the visual wulst, the retinotopy revealed by our experiments has not been illustrated convincingly before. The frontal part of the visual field (0°±30° azimuth) was not represented in the retinotopic map. The visual field from 30°–60° azimuth showed stronger magnification compared with more lateral regions. Only stimuli within elevations between about 20° and 40° above the horizon elicited neuronal activation. Activation from other elevations was masked by activation of the preferred region. Most interestingly, we observed more than one retinotopic representation of visual space within the visual wulst, which indicates that the avian wulst, like the visual cortex in mammals, may show some compartmentation parallel to the surface in addition to its layered structure.Conclusion/SignificanceOur results show the applicability of the optical imaging method also for small songbirds. We obtained a more detailed picture of retinotopic maps in birds, especially on the functional neuronal organisation of the visual wulst. Our findings support the notion of homology of visual wulst and visual cortex by showing that there is a functional correspondence between the two areas but also raise questions based on considerable differences between avian and mammalian retinotopic representations.

Serotonin 5-HT1A receptor binding sites in the brain of the pigeon (Columba livia)

“…This implicates that 5-HT 1A receptors are critically involved in the function of the avian Wulst, which is in part comparable with the function of primary visual, somatosensory and motor cortices in mammals (Keary et al, 2010;Ng et al, 2010;Reiner et al, 2005;Iwaniuk and Wylie, 2006). The avian Wulst is also a part of the thalamofugal pathway in birds Karten et al, 1973;Shimizu and Bowers, 1999).…”

Brain activation pattern depends on the strategy chosen by zebra finches to solve an orientation task

“…Within this region, Keary and colleagues (Keary et al, 2010) described retinotopic maps and, according to Watanabe and colleagues (Watanabe et al, 2011), lesions impair spatial orientation. To estimate cell density, the ocular grid was positioned in a central part of hyperpallium densocellulare and hyperpallium apicale that could be identified by anatomical landmarks.…”

The visual system of a Palaeognathous bird: Visual field, retinal topography and retino‐central connections in the Chilean Tinamou (Nothoprocta perdicaria)

“…However, in spite of large-scale comparative studies exploring the allometric variations of specific brain structures (Corfield et al, 2012;Iwaniuk et al, 2005Iwaniuk et al, , 2010, systematic anatomical and electrophysiological investigation of the avian visual system has focused on only few species: the chicken (Gallus gallus; Ehrlich and Mark, 1984a,b;Koshiba et al, 2005;Luksch et al, 2001;Verhaal and Luksch, 2013;Wang et al, 2004Wang et al, , 2006, the rock pigeon (Columba livia; Benowitz and Karten, 1976;Binggeli and Paule, 1969;Karten et al, 1973Karten et al, , 1997Letelier et al, 2004;Mar ın et al, 2003Mar ın et al, , 2012Mpodozis et al, 1995;Remy and G€ unt€ urk€ un, 1991;Shimizu et al, 1994), the quail (Coturnix coturnix; Budnik et al, 1984;Ikushima et al, 1986;Maturana and Varela, 1982;Norgren and Silver, 1989a), the barn owl (Tyto alba; Bravo and Pettigrew, 1981;Gutfreund, 2012;Gutfreund et al, 2002;Harmening and Wagner, 2011;Knudsen, 2002;Pettigrew and Konishi, 1976;Wathey and Pettigrew, 1989), and the zebra finch (Taeniopygia guttata ;Bischof, 1988;Faunes et al, 2013;Keary et al, 2010;Schmidt and Bischof, 2001;Schmidt et al, 1999); all of them pertaining to the Neognathae, the grand clade to which most...…”