Dysregulation of visual motion inhibition in major depression
Norton, Daniel J.; McBain, Ryan K.; Pizzagalli, Diego A.; Cronin-Golomb, Alice; Chen, Yue
Individuals with depression show depleted concentrations of the inhibitory neurotransmitter GABA in
occipital (visual) cortex, predicting weakened inhibition within their visual systems. Yet, visual inhibition
in depression remains largely unexplored. To fill this gap, we examined the inhibitory process of centersurround suppression (CSS) of visual motion in depressed individuals. Perceptual performance in discriminating the direction of motion was measured as a function of stimulus presentation time and
contrast in depressed individuals (n¼27) and controls (n¼22). CSS was operationalized as the accuracy
difference between conditions using large (7.5°) and small (1.5°) grating stimuli. Both depressed and
control participants displayed the expected advantage in accuracy for small stimuli at high contrast. A
significant interaction emerged between subject group, contrast level and presentation time, indicating
that alterations of CSS in depression were modulated by stimulus conditions. At high contrast, depressed
individuals showed significantly greater CSS than controls at the 66 ms presentation time (where the
effect peaked in both groups). The results' specificity and dependence on stimulus features such as
contrast, size and presentation time suggest that they arise from changes in early visual processing, and
are not the results of a generalized deficit or cognitive bias.
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