Depth-dependent functional MRI responses to chromatic and achromatic stimuli throughout V1 and V2

In the primate visual system, form (shape, location) and color information are processed in separate but interacting pathways. Recent access to high-resolution neuroimaging has facilitated the exploration of the structure of these pathways at the mesoscopic level in the human visual cortex. We used 7T fMRI to observe selective activation of the primary visual cortex to chromatic versus achromatic stimuli in five participants across two scanning sessions. Achromatic checkerboards with low spatial frequency and high temporal frequency targeted the color-insensitive magnocellular pathway. Chromatic checkerboards with higher spatial frequency and low temporal frequency targeted the color-selective parvocellular pathway. This work resulted in three main findings. First, responses driven by chromatic stimuli had a laminar profile biased towards superficial layers of V1, as compared to responses driven by achromatic stimuli. Second, we found stronger preference for chromatic stimuli in parafoveal V1 compared with peripheral V1. Finally, we found alternating, stimulus-selective bands stemming from the V1 border into V2 and V3. Similar alternating patterns have been previously found in both NHP and human extrastriate cortex. Together, our findings confirm the utility of fMRI for revealing details of mesoscopic neural architecture in human cortex.

Automated summary

In the primate visual system, form and color information are processed in separate pathways that interact with each other. Using high-resolution neuroimaging techniques, this study explored the structure of these pathways in the human visual cortex. The findings revealed differences in laminar profiles between responses driven by chromatic versus achromatic stimuli in V1, with stronger preference for chromatic stimuli in parafoveal V1 compared to peripheral V1 and the presence of stimulus-selective bands extending from V1 into V2 and V3. Overall, the utility of fMRI for elucidating mesoscopic neural architecture in the human cortex was confirmed by this study.