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Christian Casanova, Bruno Oliveira Ferreira de Souza, Cortes Nelson; Pulvinar modulation of the contrast response function of cortical neurons along the ventral pathway. Journal of Vision 2019;19(10):170a. doi: https://doi.org/10.1167/19.10.170a.
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© ARVO (1962-2015); The Authors (2016-present)
The pulvinar has extensive reciprocal connections with the visual cortex, allowing the transthalamic cortico-cortical transfer of visual information. Little is known about the nature of these connections. Classically, neuronal signals are of two types: drivers, that determine the response of their target cells, and modulators, that provide contextual control of neural responses. In the visual system, previous studies characterized thalamocortical projections from the lateral geniculate nucleus as driver while those from the pulvinar, as either drivers or modulators. Here, we characterized the driver/modulatory nature of the thalamic input by their impact on the contrast response function (CRF) of neurons from two distinct cortical areas: areas 17 and 21a. Single-unit responses to gratings presented at different contrasts were recorded in both areas using linear probes before, during and after the GABA inactivation of the lateral (LPl) or medial (LPm) parts of the lateral posterior nucleus. Based on theoretical studies, driver effects may be distinguished as an additive or subtractive effect on the CRF, while modulator acts by a multiplicative or divisive change. In area 17, LPl inactivation modified mostly the Rmax with 63% of cells showing an increased and 37% a decrease of activity. Only 3 cells showed an increase of C50. In area 21a, LPl inactivation yielded an increase in Rmax for most cells (30/35), with only 2 neurons exhibiting changes in C50. Inactivation of the LPm yielded an increase in C50 and Rmax for 1/3 of 21a cells (11/31), while for the rest, only the Rmax increased. These findings indicate that the pulvino-cortical signals are mostly modulatory in area 17 and modulatory and driver in area 21a. The distinctive influence of pulvinar across the cortical hierarchy may play a central role in visual attention mechanisms.
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