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Thomas Z. Lauritzen, Alex R. Wade; Spatial dependence of the negative BOLD response driven by achromatic and S-cone contrast. Journal of Vision 2010;10(15):44. doi: https://doi.org/10.1167/10.15.44.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: In early visual cortex, stimulus-driven increases in the blood oxygenation level-dependent (BOLD) signal measured with fMRI are frequently accompanied by reductions in the BOLD signal in adjacent regions of cortex. Although this negative BOLD response (NBR) is thought to result from neuronal suppression, the precise relationship between local activity, suppression, and perception remains unknown. We have previously shown that NBR can be modeled as a pathway-specific contrast gain modulation that is strongest outside of the fovea . Here we study the effect of the eccentricity of visual stimulation on the NBR and the effect of changing the inducing stimulus to contain pure S-cone isolating contrast.
Methods: We measured BOLD signals in human primary visual cortex while varying the eccentricity of the driving stimulus, and the baseline contrast levels in the region affected by the NBR, in both contrast and S-cone isoluminant space. Stimuli were presented in an event related design while the subjects were performing an attention task at the central fixation point. Contrast maps were generated using a GLM algorithm.
Results: We find that the NBR increases with eccentricity of the visual space. The responses are best modeled by an excitatory center with a divisive surround. There are significant differences between the NBR generated by achromatic and S-cone stimuli.
Conclusions: The NBR is generated by a divisive center-surround mechanism that is strongest in the fovea, weak in the periphery and is driven differently by S-cone and achromatic contrast.
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