An extra eye primordium was implanted into the forebrain region of embryonic Rana pipiens. During development both normal and supernumerary optic tracts terminated within a single, previously uninnervated tectal lobe. Autoradiographic tracing of either the normal or supernumerary eye's projection revealed distinct, eye-specific bands of radioactivity running rostrocaudally through the dually innervated tectum. Interactions among axons of retinal ganglion cells, possibly mediated through tectal neurons, must be invoked to explain this stereotyped disruption of the normally continuous retinal termination pattern.
"Rotation of the ipsilateral eye produces an initially rotated ipsilateral retinotopic map, but with time the nucleus isthmus projections reorient themselves to match the contralateral inputs (Udin and Keating, 1981) in a process that requires visual experience (Keating and Feldman, 1975; Udin and Keating, 1981). The importance of activity has also been demonstrated through the use of surgically implanted third eyes onto frogs, which successfully innervate the optic tectum, but form segregated bands that are distinct from those of the native eye (Constantine-Paton and Law, 1978). This segregation is blocked both with TTX and NMDA receptor antagonists (Reh and Constantine-Paton, 1985; Cline et al., 1987). "
[Show abstract][Hide abstract] ABSTRACT: Spike-timing-dependent plasticity (STDP) is found in vivo in a variety of systems and species, but the first demonstrations of in vivo STDP were carried out in the optic tectum of Xenopus laevis embryos. Since then, the optic tectum has served as an excellent experimental model for studying STDP in sensory systems, allowing researchers to probe the developmental consequences of this form of synaptic plasticity during early development. In this review, we will describe what is known about the role of STDP in shaping feed-forward and recurrent circuits in the optic tectum with a focus on the functional implications for vision. We will discuss both the similarities and differences between the optic tectum and mammalian sensory systems that are relevant to STDP. Finally, we will highlight the unique properties of the embryonic tectum that make it an important system for researchers who are interested in how STDP contributes to activity-dependent development of sensory computations.
Frontiers in Synaptic Neuroscience 06/2010; 2:7. DOI:10.3389/fnsyn.2010.00007
"We should ask why the developmental factors that lead to the ocular dominance columns were selected in evolution. We know from the experiments of Constantine-Paton and Law (1978) that transplanting an extra eye to a tadpole will result in a frog with two eyes innervating the contralateral optic tectum. For such cases, ocular dominance columns are present, even though they are never normally present and, therefore, have no normal (ecologically relevant) function. "
[Show abstract][Hide abstract] ABSTRACT: A significant concept in neuroscience is that sensory areas of the neocortex have evolved the remarkable ability to represent a number of stimulus features within the confines of a global map of the sensory periphery. Modularity, the term often used to describe the inhomogeneous nature of the neocortex, is without a doubt an important organizational principle of early sensory areas, such as the primary visual cortex (V1). Ocular dominance columns, one type of module in V1, are found in many primate species as well as in carnivores. Yet, their variable presence in some New World monkey species and complete absence in other species has been enigmatic. Here, we demonstrate that optical imaging reveals the presence of ocular dominance columns in the superficial layers of V1 of owl monkeys (Aotus trivirgatus), even though the geniculate inputs related to each eye are highly overlapping in layer 4. The ocular dominance columns in owl monkeys revealed by optical imaging are circular in appearance. The distance between left eye centers and right eye centers is approximately 650 mum. We find no relationship between ocular dominance centers and other modular organizational features such as orientation pinwheels or the centers of the cytochrome oxidase blobs. These results are significant because they suggest that functional columns may exist in the absence of obvious differences in the distributions of activating inputs and ocular dominance columns may be more widely distributed across mammalian taxa than commonly suggested.
Frontiers in Neuroscience 11/2007; 1(1):67-75. DOI:10.3389/neuro.01/1.1.005.2007 · 3.66 Impact Factor
"Firstly, experimental manipulations in the frog and goldfish have shown that when fibres from a second eye invade a region of brain which is normally innervated by only one eye, ocular dominance stripes can be formed (e.g. ). This suggests that ocular dominance may be a byproduct of the expression of the rules for topographic map formation, and does not require additional mechanisms . "
[Show abstract][Hide abstract] ABSTRACT: A new computational model that addresses the formation of both topography and ocular dominance is presented. This is motivated by experimental evidence that these phenomena may be subserved by the same mechanisms. An important aspect of this model is that ocular dominance segregation can occur when input activity is both distributed, and positively correlated between the eyes. This allows investigation of the dependence of the pattern of ocular dominance stripes on the degree of correlation between the eyes: it is found that increasing correlation leads to narrower stripes. Experiments are suggested to test whether such behaviour occurs in the natural system. 1 INTRODUCTION The development of topographic and interdigitated mappings in the nervous system has been much studied experimentally, especially in the visual system (e.g. [8, 15]). Here, each eye projects in a topographic manner to more central brain structures: i.e. neighbouring points in the eye map to neighbouring points in t...
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