The Influences Of Surround Suppression And Brain White Matter Functional Activity On Visual Information Processing

In this study,we combined psychophysical and model analyses to explore how spatial separation and moderate alcohol exposure influence surround suppression of the visual cortex,and following changes in orientation and motion direction information processing of visual system.In addition,using functional magnetic resonance imaging(fMRI),we investigated the topological organization of functional activity within white matter tracts connected different visual areas,as well as the influences of white matter functional activity on information transfer between visual areas.The surround suppression has strong effects on visual processing.Psychophysics and modeling studies have provided evidence that the surround context can systematically modulate the perception of center stimuli.For motion direction,these center-surround interactions are considered to come from spatio-directional interactions between direction of motion tuned neurons,which are attributed to the middle temporal(MT)area.Here,we investigated through psychophysics experiments on human subjects changes with spatial separation in center-surround inhibition and motion direction interactions.Center-surround motion repulsion effects were measured under near-and far-surround conditions.Using a simple physiological model of the repulsion effect we extracted theoretical population parameters of surround inhibition strength and motion tuning widths with spatial distance.We observed clear motion repulsion effect under both near-surround and far-surround conditions.The amplitude of repulsion effect under far-surround was smaller than that in near-surround.The model predicted human performance well.Surround inhibition under the near-surround condition was significantly stronger than that under the far-surround condition,and the tuning widths were smaller under the near-surround condition.These results demonstrate that spatial separation can both modulate the surround inhibition strength and surround to center tuning width.Surround suppression change has been linked to alteration in GABA-ergic inhibitory cortical function,alcohol is generally recognized as an inhibitor in the brain by potentiating GABA-ergic system.However,there is little direct behavioral evidence to show how cortical inhibitory system regulate surround suppression.In this study,we focused on visual orientation/motion processing and explored whether moderate alcohol intoxication induced changes in inhibitory mediated surround suppression.We conducted a double-blind,placebo-controlled,within-subjects study on the effect of alcohol on visual tilt illusion(TI)and motion repulsion(MR).Each subject underwent three experimental conditions(sober,placebo and moderate alcohol)on separate days.The order of the placebo and moderate alcohol conditions was counterbalanced.We found alcohol significantly increased repulsive TI and MR effect and weakened overall orientation/direction discrimination performance.We also observed no visible changes in the data for global orientation processing but a presence of global attentional modulation.Thus,our results provide psychophysics evidences that alcohol changed V1 and MT processing that affects visual perception of contextual stimuli.The functional significance of BOLD signals in white matter(WM)remains unclear.The current study investigated whether 7TBOLD signal from visual WM tracts encodes high fidelity retinotopic activity and whether it correlates with the effective connectivity between visual areas.Using the population receptive field(pRF)analysis on the 7T retinotopy dataset from Human Connectome Project,we found clear contralateral retinotopic representations from two visual WM bundles:optic radiation(OR)and vertical occipital fasciculus(VOF).The retinotopic organization of OR is consistent with post-mortem studies.The pRF size of WM voxels also increases with eccentricity.An online atlas was provided in Montreal Neurological Institute(MNI)space.Based on the retinotopic maps of OR,we investigated whether OR BOLD signals during visual stimulation can predict the resting-state effective connectivity between the lateral geniculate nucleus and the primary visual cortex.Results show that OR BOLD responses more correlated with the feedforward and feedback connectivity in the foveal and peripheral visual field,respectively.These findings demonstrate that WM BOLD signals encode high fidelity neural activity such as visual field maps,and also predict the information transmission of connected brain areas.In summary,we found spatial separation and alcohol could affect surround suppression and thus resulted in changes in orientation/direction information processing of visual system.Functional activity in visual WM has topographic organization and influences information transfor between visual areas.