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Como a retina funciona: como um quebracabeça de camadas múltiplas de campos de recepção
ScienceDaily (7 de abeil de 2009) — Cerca de 1.25 milhões de neurônios na retina — cada um deles vê o mundo somente através de uma pequena janela irregular chamada de campo receptivo — coletivamente formam a figura sem costura que nós dependemos para navegarmos em nosso ambiente. Os campos receptivos se encaixam como peças de quebracabeças evitando “pontos cegos” e sobreposição excessiva que poderiam borrar nossa percepção do mundo, de acordo com pesquisadores do Salk Institute for Biological Studies.
Mais informações, sorry periferia, mas está em inglês, aqui.
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Receptive Fields in Primate Retina Are Coordinated to Sample Visual Space More Uniformly
Jeffrey L. Gauthier1*, Greg D. Field1, Alexander Sher2, Martin Greschner1, Jonathon Shlens1,3, Alan M. Litke2, E. J. Chichilnisky1
1 Salk Institute for Biological Studies, La Jolla, California, United States of America, 2 Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, California, United States of America, 3 University of California, Berkeley, California, United States of America
In the visual system, large ensembles of neurons collectively sample visual space with receptive fields (RFs). A puzzling problem is how neural ensembles provide a uniform, high-resolution visual representation in spite of irregularities in the RFs of individual cells. This problem was approached by simultaneously mapping the RFs of hundreds of primate retinal ganglion cells. As observed in previous studies, RFs exhibited irregular shapes that deviated from standard Gaussian models. Surprisingly, these irregularities were coordinated at a fine spatial scale: RFs interlocked with their neighbors, filling in gaps and avoiding large variations in overlap. RF shapes were coordinated with high spatial precision: the observed uniformity was degraded by angular perturbations as small as 15°, and the observed populations sampled visual space with more than 50% of the theoretical ideal uniformity. These results show that the primate retina encodes light with an exquisitely coordinated array of RF shapes, illustrating a higher degree of functional precision in the neural circuitry than previously appreciated.
Funding. This work was supported by the National Insitutes of Health (NIH) National Research Service Award (NRSA) (1 F31 NS054519–01) and the Chapman Foundation (JLG), Helen Hay Whitney Foundation (GDF), Burroughs Wellcome Fund Career Award at Scientific Interface (AS), Deutscher Akademischer Austausch Dienst (DAAD) (MG), National Science Foundation (NSF) Integrative Graduate Education and Research Traineeship (IGERT) DGE-033451 (JS), McKnight Foundation (AML and EJC), NSF Grant PHY-0417175 (AML), and NIH Grant EY017992 (EJC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests. The authors have declared that no competing interests exist.
Academic Editor: Michael Robert DeWeese, University of California, Berkeley, United States of America
Citation: Gauthier JL, Field GD, Sher A, Greschner M, Shlens J, et al. (2009) Receptive Fields in Primate Retina Are Coordinated to Sample Visual Space More Uniformly. PLoS Biol 7(4): e1000063 doi:10.1371/journal.pbio.1000063
Received: February 13, 2008; Accepted: February 6, 2009; Published: April 7, 2009
Copyright: © 2009 Gauthier et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Abbreviations: DF, dendritic field; RF, receptive field; SEM, standard error of the mean; STA, spike-triggered average; UI, uniformity index
* To whom correspondence should be addressed. E-mail: gauthier@salk.edu
AUTHOR INTRODUCTION
All visual information reaching the brain is transmitted by retinal ganglion cells, each of which is sensitive to a small region of space known as its receptive field. Each of the 20 or so distinct ganglion cell types is thought to transmit a complete visual image to the brain, because the receptive fields of each type form a regular lattice covering visual space. However, within each regular lattice, individual receptive fields have jagged, asymmetric shapes, which could produce “blind spots” and excessive overlap, degrading the visual image. To understand how the visual system overcomes this problem, we used a multielectrode array to record from hundreds of ganglion cells in isolated patches of peripheral primate retina. Surprisingly, we found that irregularly shaped receptive fields fit together like puzzle pieces, with high spatial precision, producing a more homogeneous coverage of visual space than would be possible otherwise. This finding reveals that the representation of visual space by neural ensembles in the retina is functionally coordinated and tuned, presumably by developmental interactions or ongoing visual activity, producing a more precise sensory signal.
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PDF do artigo gratuito aqui. [5.64 MB]
