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Christian Casanova, Azaheh Naderiyanha, Matthieu Vanni; Visual cortex responses to visual and electrical stimulations recorded by voltage sensitive dye imaging in cats and tree shrews. Journal of Vision 2011;11(11):297. doi: https://doi.org/10.1167/11.11.297.
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© ARVO (1962-2015); The Authors (2016-present)
It is well known that the primary visual cortex received its main thalamic drive from the lateral geniculate nucleus (LGN) through layer IV. In contrast, projections from the lateral posterior (LP) -pulvinar complex end for the most part in layer I, suggesting that LP-pulvinar exerts a diffuse modulatory influence on activity of the primary visual cortex. If that is the case, one would expect the spatio-temporal responses evoked by activation of these two pathways to be different. We investigated this issue by measuring the spatiotemporal dynamics of voltage sensitive dyes activation in the visual cortex following thalamic electrical stimulation in two different species: cats and tree shrews. Responses were compared to those evoked by visual stimuli (flashing squares and drifting gratings). Animals were anesthetized with halothane. RH1691 dye was used to stain the cortex. Stimulating electrodes were placed in the LGN and LP-pulvinar complex. Cortical responses evoked by flashing squares were observed in regions extending to several millimeters. At the activation site, positive responses were maximal at 90 ms, while in surrounding regions, negatives responses were observed (followed by activation). In cats, this profile was observed at the onset and offset of the square, while in tree shrew, it was only for the stimulus appearance. For gratings, orientation selectivity exhibited a tonic profile in cats, but a more transient one in tree shrews. Electrical stimulation of LGN induced a complex response comprising a fast positive component followed by a slow biphasic one. In surrounding and contralateral cortices, negative responses were observed, followed by activation. Electric stimulation of pulvinar did not induce any responses but strongly reduced the slow LGN-induced biphasic responses. In conclusion, stimulus inputs induce complex (species-selective) mechanisms of excitation/inhibition in time and space which involve cortical networks as well as thalamic modulation.
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