Non-Neural Factors Influencing BOLD Response Magnitudes within Individual Subjects

Jan W. Kurzawski, Omer Faruk Gulban, Keith Jamison, Jonathan Winawer, Kendrick Kay

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


To what extent is the size of the blood-oxygen-level-dependent (BOLD) response influenced by factors other than neural activity? In a re-analysis of three neuroimaging 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 surprising 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 variation 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, indicating that some of the difference is likely not due to neural activity differences. We conclude that interpretation of variation in BOLD response magnitude across cortical locations should consider the influence of the potential confounding factors of thickness, curvature, depth and vascularization. SIGNIFICANCE STATEMENTThe magnitude of the BOLD signal is often used as a surrogate of neural activity, but the exact factors that contribute to its strength have not been studied on a voxel-wise level. Here, we examined several anatomical and measurement-related factors to assess their relationship with BOLD signal magnitude. We find that BOLD magnitude correlates with cortical anatomy, depth and macrovasculature. To remove the contribution of these factors, we propose a simple, data-driven correction method that can be used in any functional magnetic resonance imaging (fMRI) experiment. After accounting for the confounding factors, BOLD magnitude becomes more spatially homogenous. Our correction method improves the ability to make more accurate inferences about local neural activity from fMRI data.

Original languageEnglish (US)
Pages (from-to)7256-7266
Number of pages11
JournalJournal of Neuroscience
Issue number38
StatePublished - Sep 21 2022

Bibliographical note

Funding Information:
Received Dec. 26, 2021; revised June 15, 2022; accepted Aug. 3, 2022. Author contributions: J.W.K., J.W., and K.K. designed research; J.W.K., J.W., and K.K. performed research; J.W.K., K.J., and K.K. analyzed data; J.W.K., J.W., and K.K. wrote the first draft of the paper; J.W.K., O.F.G., J.W., and K.K. edited the paper; J.W.K., J.W., and K.K. wrote the paper. This work was supported by National Eye Institute R01-EY027964, R01-MH111417, and R01-EY027401 to J. W. Collection of the NSD dataset was supported by National Science Foundation CRCNS Grant IIS-1822683 to K.K.; and National Science Foundation Grant IIS-1822929. *J.W. and K.K. contributed equally to this work as co-senior authors. The authors declare no competing financial interests. Correspondence should be addressed to Jan W. Kurzawski at Copyright © 2022 the authors

Publisher Copyright:
Copyright © 2022 the authors.


  • BOLD signal
  • fMRI
  • meridian
  • vasculature

Center for Magnetic Resonance Research (CMRR) tags

  • MFMM

PubMed: MeSH publication types

  • Journal Article


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