The spatiotemporal hemodynamic response function for depth-dependent functional imaging of human cortex.
The gray matter of human cortex is characterized by depth-dependent differences in neuronal activity and connections (Shipp, 2007) as well as in the associated vasculature (Duvernoy et al., 1981). The resolution limit of functional magnetic resonance imaging (fMRI) measurements is now below a millimeter, promising the non-invasive measurement of these properties in awake and behaving humans (Muckli et al., 2015; Olman et al., 2012; Ress et al., 2007). To advance this endeavor, we present a detailed spatiotemporal hemodynamic response function (HRF) reconstructed through the use of high-resolution, submillimeter fMRI. We decomposed the HRF into directions tangential and perpendicular to the cortical surface and found that key spatial properties of the HRF change significantly with depth from the cortical surface. Notably, we found that the spatial spread of the HRF increases linearly from 4.8mm at the gray/white matter boundary to 6.6mm near the cortical surface. Using a hemodynamic model, we posit that this effect can be explained by the depth profile of the cortical vasculature, and as such, must be taken into account to properly estimate the underlying neuronal responses at different cortical depths.
School of Psychology, University of Wollongong, Wollongong, NSW 2522, Australia. Electronic address: pucketta@alumni.msoe.edu.
Alexander M
AM
Puckett
School of Physics, University of Sydney, Sydney, NSW 2006, Australia; Center for Integrative Brain Function, QIMR Berghofer Medical Research Institute, Herston, QLD 4006, Australia; Center for Integrative Brain Function, University of Sydney, Sydney, NSW 2006, Australia; Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire NG7 2RD, United Kingdom.
Kevin M
KM
Aquino
School of Physics, University of Sydney, Sydney, NSW 2006, Australia; Center for Integrative Brain Function, University of Sydney, Sydney, NSW 2006, Australia.
P A
PA
Robinson
Center for Integrative Brain Function, QIMR Berghofer Medical Research Institute, Herston, QLD 4006, Australia; Metro North Mental Health Service, Royal Brisbane and Women's Hospital, Herston, QLD 4029, Australia.
Michael
M
Breakspear
School of Psychology, University of Wollongong, Wollongong, NSW 2522, Australia; Neuroscience Research Australia, Randwick, NSW 2031, Australia.
Mark M
MM
Schira
D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000098:blood supply* / Q000502:physiology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D000069336:Neurovascular Coupling; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult
Hemodynamic response; High-resolution; Human; Layers; Visual cortex; fMRI