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A. Dorsal view of goldfish brain. Reproduced by kind permission of M.A. Gibbs. B. Goldfish brain cross section. Adapted from Meek J. (1983) Brain Research Reviews 6: 247-297 with permission C. Left tectum and TL showing paths of marginal fibers from 5 points in TL. Dashed curve on tectum is representation of visual field equator. D. Right visual field showing equator (dashed line), tectal MURFs (small circles), TL receptive fields (larger areas). Cb cerebellum, IC intertectal commissure, OB olfactory bulb, OT optic tectum, Teg tegmentum, Tel telencephalon, TL torus longitudinalis, TS torus semicircularis, VCb valvula of the cerebellum.
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Abstract
The optic tectum forms the roof of the midbrain and is the primary visual center in fishes. The retina and input from other sensory modalities (auditory, lateral line, somatosensory, electrosensory) are mapped topographically over tectum, where the locations of objects and events in body-centered space are represented. Tectum, via its conn...
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... tectum, the Latin for roof, covers the midbrain. In teleost fishes it is a twin-lobed canopy of neural tissue inflated over a fluid-filled ventricle. The two lobes are connected at the midline by the tectal commissure, and at their bottom edges merge with the tegmentum, the floor of the midbrain (see Fig. 4 B). A well-developed tectum in a highly visual teleost may be 0.8 mm thick with a clearly layered appearance when examined under the microscope. The layering scheme shown in Fig. 2 represents the most common interpretation of tectal structure (see Glossary for the Latin names of the 6 layers). Functionally, the most important distinction ...
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... torus longitudinalis, TL, which occurs only in teleost fishes, consists of a pair of elongated cell masses connected to the medial margins of the tectum, lying just below the intertectal commissure, a thin band of fibers that connects the two tectal lobes (Fig. 4 A, B). Large numbers of small neurons in each TL (100,000 in goldfish) send an abundance of fine, unmyelinated axons into the SM, the most superficial layer of the adjacent tectum, where they course in parallel over the tectal lobe (see Fig. 4 C, Fig. 5). Indeed, SM, is filled with these TL axons, called marginal fibers, together with ...
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... lying just below the intertectal commissure, a thin band of fibers that connects the two tectal lobes (Fig. 4 A, B). Large numbers of small neurons in each TL (100,000 in goldfish) send an abundance of fine, unmyelinated axons into the SM, the most superficial layer of the adjacent tectum, where they course in parallel over the tectal lobe (see Fig. 4 C, Fig. 5). Indeed, SM, is filled with these TL axons, called marginal fibers, together with the dendrites of tectal neurons (mainly type I) onto which they synapse. The synaptic contacts made by the marginal fibers may outnumber all other inputs to tectum. The type I neurons, with cell bodies in SFGS, have extensively branched dendritic trees ...
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... the dark and is reduced by illumination. This sustained dimming activity can also be evoked by dark objects. It shows a clear retinotopic character so that an electrode in the front of TL picks up activity to dimming in the front of the visual field; positions farther back in TL have dimming receptive fields farther back in the visual field (see Fig. 4 ...
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... stimulation of a point in TL sends impulses along a beam of marginal fibers across tectum (see Fig. 4 C). This beam passes over a point in SFGS with a MURF that overlaps the receptive field of the TL point that was stimulated (Fig. 4 D). To complete the loop from tectum back to TL, type X cells connect topographically to dorsomedial TL. It is noteworthy that this tectum-dorsomedial-TL loop appears to be concerned only with dimming and ...
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... stimulation of a point in TL sends impulses along a beam of marginal fibers across tectum (see Fig. 4 C). This beam passes over a point in SFGS with a MURF that overlaps the receptive field of the TL point that was stimulated (Fig. 4 D). To complete the loop from tectum back to TL, type X cells connect topographically to dorsomedial TL. It is noteworthy that this tectum-dorsomedial-TL loop appears to be concerned only with dimming and with retinal location of a light stimulus; it is totally unconcerned with stimulus color, shape, or motion. That dimming is a separate ...
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... the optic tectum is peeled away, one sees lying along the midline, the valvula of the cerebellum, a tongue-like protrusion of the cerebellum, and flanking it, two crescent- shaped bodies, the torus semicircularis (TS) (see Fig. 4 B). Its corresponding structure in mammals is the inferior colliculus, an auditory center. On anatomic grounds, TS is another potentially important partner with the optic tectum, having reciprocal connections with it. Each TS sends axons to both tectal lobes, but each tectal lobe sends axons to TS only on the same side. TS is a large ...
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... Both rods and cones converge onto retinal ganglion cells, the axons of which form the optic nerves and optic tracts that project to the optic tectum (Northmore, 2011). Light sensitivity is improved through increasing rod convergence to ganglion cells, and as a result, tens or even hundreds of rods may converge onto a single cell (Hughes, 1977;Warrant, 1999Warrant, , 2004Joselevitch & Kamermans, 2009). ...
Understanding how organismal design evolves in response to environmental challenges is a central goal of evolutionary biology. In particular, assessing the extent to which environmental requirements drive general design features among distantly related groups is a major research question. The visual system is a critical sensory apparatus that evolves in response to changing light regimes. In vertebrates, the optic tectum is the primary visual processing center of the brain, and yet it is unclear how, or whether this structure evolves while lineages adapt to changes in photic environment. On one hand, dim‐light adaptation is associated with larger eyes and enhanced light‐gathering power that could require larger information processing capacity. On the other hand, dim‐light vision may evolve to maximize light sensitivity at the cost of acuity and color sensitivity, which could require less processing power. Here, we use X‐ray microtomography and phylogenetic comparative methods to examine the relationships between diel activity pattern, optic morphology, trophic guild, and investment in the optic tectum across the largest radiation of vertebrates—teleost fishes. We find that despite driving the evolution of larger eyes, enhancement of the capacity for dim‐light vision generally is accompanied by a decrease in investment in the optic tectum. These findings underscore the importance of considering diel activity patterns in comparative studies and demonstrate how vision plays a role in brain evolution, illuminating common design principles of the vertebrate visual system.
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... The central visual processing unit in the fish brain is the optic tectum (Northmore, 2011) which receives information directly from the retina on the opposite side. In addition, the visual layers of the optic tectum receive information from several pretectal areas which receive information from the retina and then relay it to the optic tectum. ...
... Since the optic tectum is the main visual processing unit in fish (Northmore, 2011), many studies have been devoted to it. However, most research on the optic tectum's visual cells has focused on their receptive field classification in terms of direction selectivity. ...
Many studies have yielded valuable knowledge on the early visual system but it is biased since the studies have focused on terrestrial mammals alone. Here, to better account for visual systems in different environments and animal classes, we studied the structure of early visual processing in the archerfish which harnesses its extreme visual ability to hunt by shooting water jets at prey hanging on vegetation above the water. Thus, the archerfish provides a unique opportunity to study visual processing in a vertebrate which is an expert vision-guided predator with a very different brain structure than mammals. The receptive field structures in the archerfish (both sexes) optic tectum, the main visual processing region in the fish brain, were measured and linear non-linear cascades were used to analyze their properties. The findings indicate that the spatial receptive field structures lie on a continuum between circular and elliptical shapes. In addition, the cells' functional properties display a richness of response characteristics, since many cells could be captured by more than a single linear filter. Finally, the non-linear response functions that link linear filters and neuronal responses were found to be similar to the non-linear functions of models that describe terrestrial mammalian single cell activity. Overall our results help to better understand the early visual processing system across vertebrates.
... Other cerebellar-like parallel fiber systems in fishes appear as mechanisms that learn to subtract self-produced effects, in this case, eye movements, by analogy with parallel fiber system in the electrosensory lobe of mormyrid electric fish (Sawtell & Bell, 2008). Therefore, Northmore (2011) suggested that the two kinds of TL activity could be used to predict the effects of eye movement on the perceived scene so that they could be discounted, providing visual stability across saccades. The puzzle that none of these ideas has solved is why two very disparate types of information, photic and saccadic, should be brought together in the dendritic trees of pyramidal cells and how this combination could do something so useful and for so long that it is used by half the vertebrate species on earth. ...
... It should also be capable of tracking an object with its attentional locus as the object's image moves smoothly across the retina. Such a pointer network in teleosts is assumed to reside in the optic tectum because it has the most detailed retinotopic map in the teleost brain and is essential for visual spatial processing (Northmore, 2011). The pointer network shown in Fig. 2 is modelled by a two-dimensional, 15 Â 11 layer of IAC units. ...
... Critical to the model is the role ascribed to the tectal pyramidal cells as a visual attentional pointer. Although there is no experimental data to support such a role, the optic tectum in teleost fishes is essential for visual orienting and pattern vision (Northmore, 2011) and evidence is accumulating that its homologue in other vertebrates is important in selective visual attention (Knudsen, 2011). The little that is known of teleost pyramidal cell physiology is consistent with the model in that pyramidal cells can be excited visually with relatively large receptive fields, while also responding with inhibitory post-synaptic potentials (Guthrie & Sharma, 1991). ...
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