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Christian Casanova, Jimmy Lai, Sébastien Thomas; Impact of pulvinar on contrast response functions in the primary visual cortex. Journal of Vision 2014;14(10):1408. doi: https://doi.org/10.1167/14.10.1408.
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The pulvinar, the largest extrageniculate thalamic visual nucleus, establishes reciprocal connections with virtually all the visual cortical areas of the brain. The pulvinar is thus in a strategic position to influence different levels of cortical processing through "driver" or "modulatory" synapses. It is generally considered that, in all species, projections from the pulvinar to the primary visual cortex (V1) are modulatory, altering decoding properties of neurons without changing their basic receptive field properties. Results from our laboratory, based on optical imaging responses evoked by electrical stimulation, support this assumption to some extent (Vanni et al. 2011, Soc. Neurosci. Abstr.). We further investigated this issue by recordings cells in V1 during the reversible inactivation of the lateral posterior nucleus (LP) - pulvinar complex in the cat. Neurons in V1 were recorded before, during and after the inactivation of the striato-recipient zone of the LP-pulvinar complex with microinjections of GABA. Recording and injection electrodes were positioned such that thalamic and cortical receptive fields overlapped. No change in the preferred orientation or direction selectivity of V1 neurons was observed during pulvinar inactivation. However, for a majority of the cells tested (n=39/58), the response amplitude to the optimal stimulus was reduced by a mean of 66%. The contrast response function of neurons was modeled with the Naka-Rushton function: Rmax(Cn/Cn+Cn50)+b. Analysis of the effects of pulvinar inactivation on the contrast response function of V1 cells revealed the existence of at least three types of modulation. These modulations were classified according to the predominantly affected curve parameter: Nine cells exhibited a decrease in Rmax, five cells had an increase in the exponential factor (n), and four units had a C50 increase. These results indicate that the pulvinar can modulate the activity of V1 neurons by modifying the profile of their contrast response function.
Meeting abstract presented at VSS 2014
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