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Jose-Manuel Alonso; Receptive field dynamics and response gain in visual thalamus. Journal of Vision 2008;8(17):4. doi: 10.1167/8.17.4.
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The Lateral Geniculate Nucleus (LGN) of the thalamus is the main entrance of visual information to the cerebral cortex and its functional role has been frequently compared with a simple gate that regulates information transfer. This concept of a passive gate, which implies that there is no major receptive field transformation from retina to LGN, is supported by two well-accepted findings. First, the LGN receptive fields are very similar to the receptive fields from their retinal inputs. And second, LGN visual responses are strongly dominated by the input from a single retinal afferent. In the first part of the talk, I will challenge the concept of a passive gate by showing that, while the fundamental structure of individual receptive fields (center-surround) is the same in LGN and retina, the tiling of the receptive field arrays is very different. I will argue that LGN receptive field arrays are more spatiotemporally diverse and that this enhanced diversity results from the divergence and convergence patterns of retinogeniculate connections (Alonso et al., 2006).
The notion that the LGN functions as a passive gate has been challenged in the past by the finding that most excitatory synapses in LGN originate in the brain stem and visual cortex but not the retina. In the second part of the talk, I will show that changes in the level of alertness in awake animals (likely mediated by the brain stem), can double the amplitude of visual responses and dramatically increase the bandwidth of temporal frequency tuning in LGN (Cano et al., 2006; Bezdudnaya et al., 2006). Remarkably, these pronounced changes in response amplitude and temporal tuning can be accomplished without altering the contrast sensitivity and receptive field size of LGN cells. Therefore, these results demonstrate that the abundant excitatory synapses from the brain stem can have a powerful effect in LGN function without necessarily altering the basic receptive field structure of LGN neurons.
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BezdudnayaT.CanoM.BereshpolovaY.StoelzelC. R.AlonsoJ. M.SwadlowH. A. (2006). Thalamic burst mode and inattention in the awake LGNd. Neuron 49(3): 421–432. PubMed ID:16446145.
CanoM.BezdudnayaT.SwadlowH. A.AlonsoJ. M. (2006). Brain state and contrast sensitivity in the awake visual thalamus. Nat Neurosci 9(10): 1240–1242. PubMed ID:16964255.
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