Effects of top-down influence suppression on behavioral and V1 neuronal contrast sensitivity functions in cats. Jian Ding et al.

The relative contributions of higher-order cortical areas and the primary visual cortex (V1) to visual perception remains poorly understood. In this study, we investigated the top-down influence of area 7 (A7), a high-level visual cortical area of cat, on both the behavioral contrast sensitivity function (CSF) and neuronal contrast sensitivity function estimated from visually evoked field potentials (VEPs) in V1. Top-down influence of A7 was noninvasively modulated using transcranial direct current stimulation (tDCS). We found that suppressing top-down influence with cathode (c)-tDCS but not sham (s)-tDCS of A7 significantly decreased both behavioral and neuronal contrast sensitivities (CS) in the same range of spatial frequencies (SFs), and significantly increased both the behavioral and neuronal contrast thresholds over a range of external noise. The neuronal CSF and TvC were highly correlated with their behavioral counterparts both before and after suppression of the top-down influence. Analysis of the TvC functions based on the Perceptual Template Model (PTM) indicated that suppression of top-down influence increased internal additive noise and the impact of external noise at both the behavioral and neuronal levels. Taken together, these results suggest that top-down influence of A7 increases both behavioral and V1 neuronal contrast sensitivity by reducing internal additive noise and the impact of external noise.