Skip to main content
Fig. 3 | EvoDevo

Fig. 3

From: Amphioxus, motion detection, and the evolutionary origin of the vertebrate retinotectal map

Fig. 3

Conservation of tectum topology during the transition from a pair of flat receptor arrays to image-forming eyes. For the sake of argument, the projection is shown as ipsilateral. Contralateral projections predominate in vertebrates, but when and why this feature evolved is beyond the scope of this account. a The starting point, a pair of flat receptor fields (each a proto-retina, as in Fig. 2e) with projections to a proto-tectum. The assumption is that the latter already receives input from an overlying array of dorsal photoreceptors, so a shadow moving across the receptor field in an anteroposterior direction (A-P, arrow) or dorsoventrally (d-v, in contrasting colors) would map to the proto-tectum with no change in orientation. Assuming also that fibers from each proto-retina accommodated to this, all arrows would point in the same direction. b Image reversal in a flat receptor array with a raised pigmented rim, to show how differential shading by a rim of even modest height reverses the polarity of the response: a light source moving in an anterior-to-posterior direction (yellow to red) stimulates the receptors in a posterior-to-anterior sequence (yellow first, red second). c The projection from an image-forming eye whose aperture, with or without a lens, reverses the visual field. Mapping the output to a tectum where the topology is fixed relative to the external world requires the projection to reverse the image a second time, which in fact is what the vertebrate retinotectal projection does [22], so the nasal quadrant of the retina, for example, (N, shown as anterior in this diagram) would map to the caudal tectum

Back to article page