Characterizing spatial heterogeneity of BOLD fMRI cortical-depth profiles of activation: the average profile may not be typical

Motivation: Laminar-fMRI analysis routinely averages cortical-depth profiles within an ROI to estimate a typical laminar activation profile and increase SNR. Previous studies suggested heterogeneity of cortical-depth profiles measured with GE-BOLD-fMRI, therefore the assumption that profiles inside ROI are similar may not hold. Goal(s): To test whether the average cortical-depth profile is typical for the whole ROI. Approach: We applied k-means clustering to identify cortical locations within an ROI with similar BOLD-fMRI cortical-depth profiles. Results: Cortical-depth profiles vary substantially across the activated region and therefore the average response profile inside the ROI may not be resemble that of any particular activated location. Impact: In laminar-fMRI analysis, due to heterogeneity of neuronal responses and/or vascular architecture the average cortical-depth profile within an ROI may not match the profile at any one location, suggesting that averaging may lose meaningful layer-specific information within the activated region.