Event Abstract Back to Event Contrast dependence of spatial frequency tuning in macaque LGN The classical model of visual neurons in the lateral geniculate nucleus (LGN) holds that their receptive fields are composed of a small center mechanism and larger surround mechanism, each Gaussian in sensitivity distribution, and that responses are determined by the difference in activation of center and surround. This difference of Gaussians (DoG) model predicts that, when tested with drifting sinusoidal gratings of different spatial frequency, the neuron's spatial frequency tuning can be modeled as the difference of two Gaussians. Many studies have confirmed that this model provides a good account of response data obtained at high contrast, or of contrast sensitivity data obtained by measuring gain at low contrast. The DoG model assumes that the underlying receptive field mechanisms are fixed in size, and therefore predicts that spatial frequency tuning curves measured at different contrasts should be scaled replicas of one other. We examined this question by recording extracellularly from neurons in the LGN of anesthetized macaques and measuring their responses to large gratings of optimal drift rate that varied over a wide range of spatial frequency and contrast. The shapes of spatial frequency tuning curves varied with contrast for most M- and P-cells we studied. In particular, as stimulus contrast increased, responses to high spatial frequencies grew more rapidly than responses to low spatial frequencies, resulting in an overall rightward shift in the tuning curve and a concomitant increase in the peak frequency. We fit the tuning data for each contrast with a separate DoG and examined the model parameters. As contrast increased, the size of both the center and surround mechanisms decreased systematically with increasing contrast, while the relative gain of the two mechanisms remained roughly constant. A related analysis of LGN cells in the cat (Bonin et al., J Neurosci, 2005) proposed a third suppressive mechanism, large in spatial extent, to account for contrast dependent spatial summation. Such a mechanism might be at work in our M-cells, but cannot account for the contrast-dependent changes in P-cells, which show no signs of a suppressive surround. Our data are consistent with a modified DoG model in which both the center and surround sizes decrease as a function of contrast. This could be conveniently explained by a contrast dependent change in the scale of spatial integration of a single mechanism, presumably in retina, whose signals contribute to both center and surround. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). Contrast dependence of spatial frequency tuning in macaque LGN. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.174 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Feb 2009; Published Online: 03 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.