Non-Neural Factors Influencing BOLD Response Magnitudes within Individual Subjects

To what extent is the size of the BOLD response influenced by factors other than neural activity? In a reanalysis of three neu-roimaging datasets (male and female human participants), we find large systematic inhomogeneities in the BOLD response magnitude in primary visual cortex (V1): stimulus-evoked BOLD responses, expressed in units of percent signal change, are up to 50% larger along the representation of the horizontal meridian than the vertical meridian. To assess whether this sur-prising effect can be interpreted as differences in local neural activity, we quantified several factors that potentially contribute to the size of the BOLD response. We find relationships between BOLD response magnitude and cortical thickness, curvature, depth, and macrovasculature. These relationships are consistently found across subjects and datasets and suggest that varia-tion in BOLD response magnitudes across cortical locations reflects, in part, differences in anatomy and vascularization. To compensate for these factors, we implement a regression-based correction method and show that, after correction, BOLD responses become more homogeneous across V1. The correction reduces the horizontal/vertical difference by about half, indi-cating that some of the difference is likely not because of neural activity differences. We conclude that interpretation of varia-tion in BOLD response magnitude across cortical locations should consider the influence of the potential confounding factors of thickness, curvature, depth, and vascularization.

Automated summary

In this study, three neuroimaging datasets were reanalyzed, and it was found that there is a significant difference in the magnitude of the BOLD response in different locations of the primary visual cortex (V1). This difference may be related to the thickness, curvature, depth, and vascularization of the cortex. After correction, the difference in BOLD response decreased by half, suggesting that some of the differences may not be caused by neural activity.