Modulation of the contrast response function of V1 neurons by the pulvinar

Abstract

PurposeThe pulvinar establishes reciprocal connections with nearly all the visual cortices and is thus in a strategic position to influence analyses taking place at the cortical level. Projections from the pulvinar to the primary visual cortex (V1) are considered to be modulatory, altering decoding properties of neurons without changing their basic receptive field properties. Results from our laboratory, based on optical imaging, have supported this assumption (Soc. Neurosci. Abst. 2011. Vanni et al.).MethodsHere, we investigate further by studying V1 single unit responses during reversible deactivation of the lateral posterior (LP) – pulvinar complex in the cat through microinjections of gamma‐aminobutyric acid. Recording and injection electrodes were positioned to obtain overlapping thalamic and cortical receptive fields.ResultsNo change in the preferred orientation or direction selectivity of V1 neurons was observed during pulvinar deactivation. However, for 67% of the cells tested (n = 39/58), the response amplitude to the optimal stimulus was reduced by a mean of 65%. The contrast response function of neurons was modeled with the Naka‐Rushton function and analysis of the effects of pulvinar deactivation revealed at least three types of modulation based on the function parameter predominantly affected: 24% of cells had a decrease in Rmax, 13% had an increase in the exponential factor and 11% had a C50 increase.ConclusionsOur results suggest that the pulvinar modulates activity of neurons in the primary visual cortex in a contrast‐dependent manner. Consequently, this extrageniculate nucleus is likely to contribute to cortical processing in shaping spatiotemporal activity patterns of V1 neurons.