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Christian Casanova, Bruno Oliveira Ferreira de Souza, Nelson Cortes Hernandez; Modulation of the visual cortex contrast response function by the pulvinar. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2591.
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© ARVO (1962-2015); The Authors (2016-present)
It is generally considered that neural signals transmitted between the thalamus and the cortex are of two types: driver inputs that determine the response of their target cells, and modulators, that provide contextual control of existing neural responses. In the visual system, it is well established that thalamocortical projections from the lateral geniculate nucleus are drivers while those originating from the pulvinar, are either drivers or modulators, according to the recipient layer. We explored here the possibility that the driver/modulatory nature of the thalamic input could be recognized by their distinct impact on the contrast response function (CRF) of visual cortical neurons.
We tested this hypothesis by measuring CRF of cortical neurons in the primary visual cortex and in a higher-order area (21a) of the cat before and after the modulation of the activity of the pulvinar. Areas 17 and 21a received their main pulvinar input through layers I and IV, respectively. Animals were anesthetized and recordings were made across all layers with multichannel electrodes. The intracerebral injection of GABA was done to silence pulvinar neurons. Cortical response properties, including contrast selectivity, were studied using drifting gratings.
A total of 142 neurons were recorded in areas 17 and 21a. Inactivation of the pulvinar provoked a reduction of the amplitude of the CRF of area 17 cells in supragranular layers while the dynamic range of the CRF decreased in infragranular layers. In contrast, pulvinar silencing produced more homogeneous changes since the majority of neurons increased their discharges. Specific properties such as orientation and direction tuning as well as spatial and temporal frequency selectivity were not altered.
Our findings support the notion that pulvinar projections to cortical neurons in area 17 are principally modulatory in nature but, in case of area 21a, do not support the link between the cortical layer position and the nature of the incoming thalamic input. It indicates that thalamic signals can control the contrast gain of neurons in cortical areas without altering the cell stimulus selectivity. Further, it suggests that pulvinar may be involved in attentional related changes of the contrast sensitivity function in humans.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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