The role of inhibition in formatting visual information in the retina and LGN
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1
University of Maryland , Deparment of Biology and Program in Neuroscience, United States
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2
Cooper Union School of Engineering , United States
Despite being well characterized anatomically and physiologically, our understanding of how the visual pathway processes information is relatively impoverished, due in part to our reliance of the "receptive field" as a description of neuronal function. The linear receptive field describes the average visual stimulus that a neuron responds to, and is known to break down in describing cortical neurons (such as "complex cells"), whose response is known to involve nonlinear combinations of more than one visual feature. In fact, even processing in the retina and lateral geniculate nucleus (LGN) involves the combination of multiple stimulus features, due to the presence of inhibitory interneurons at each stage. However, it has not been clear what role such inhibition plays, and how it contributes to neuronal processing, in part because single receptive-field-based descriptions of these neurons cannot separate the effects of excitation and inhibition. Here we apply a new General Nonlinear Modeling (GNM) framework to simultaneously recorded pairs consisting of an LGN neuron and the retinal ganglion cell (RGC) that provides its main input. This modeling framework associates nonlinear processing with each stimulus-processing element, and thus can combine the influences of multiple stimulus-tuned elements to predict the observed spike train. By recording from successive stages of processing simultaneously, we can furthermore distinguish the processing that occurs in the retina from processing that occurs in the LGN, and understand how visual information is successively formatted for the visual cortex. We detect separate putative inhibitory elements that affect processing both in the retina and the LGN. We find that RGCs consistently have a strong inhibitory input that has similar tuning to its excitatory tuning, but delayed in time. This makes RGC responses more precise in time, because the inhibition attenuates the response earlier than the decay of excitation. At the level of the LGN, a second inhibitory input is added, except in this case it is an "opposite-sign", or "pull" inhibition. Additionally, the effects of the "same-sign" inhibition inherited from the retina are much more evident, and combined with the higher threshold and pull inhibition, result in temporally precise, sparse responses. We further probe these mechanisms by looking at their effects as a function of contrast. This reveals that the strength of inhibition changes relative to excitation, and all but disappears at low contrast. This suggests several observed effects of contrast gain control, such as changes in gain, temporal sensitivity, and latency, might be a result of the interplay of excitation with delayed inhibition, and potentially reveals a contrast-independent function of the underlying circuitry. Thus, inhibition likely plays a role at multiple levels in formatting visual information for the visual cortex. By revealing how visual information is "formatted" in the early visual pathway, we provide insight into what is likely relevant to the cortex. Furthermore, we present a general method for probing the role of inhibition in other sensory areas.
Conference:
Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010.
Presentation Type:
Poster Presentation
Topic:
Poster session I
Citation:
Butts
DA and
Casti
AR
(2010). The role of inhibition in formatting visual information in the retina and LGN.
Front. Neurosci.
Conference Abstract:
Computational and Systems Neuroscience 2010.
doi: 10.3389/conf.fnins.2010.03.00153
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Received:
02 Mar 2010;
Published Online:
02 Mar 2010.
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Correspondence:
Daniel A Butts, University of Maryland, Deparment of Biology and Program in Neuroscience, College Park, MD, United States, dab@umd.edu