title: Arterial impulse model for the BOLD response to brief neural activation.
abstract: The blood oxygen level dependent (BOLD) signal evoked by brief neural stimulation, the hemodynamic response function (HRF), is a critical feature of neurovascular coupling. The HRF is directly related to local transient changes in oxygen supplied by cerebral blood flow (CBF) and oxygen demand, the cerebral metabolic rate of oxygen (CMRO2). Previous efforts to explain the HRF have relied upon the hypothesis that CBF produces a non-linear venous dilation within the cortical parenchyma. Instead, the observed dynamics correspond to prompt arterial dilation without venous volume change. This work develops an alternative biomechanical model for the BOLD response based on the hypothesis that prompt upstream dilation creates an arterial flow impulse amenable to linear description. This flow model is coupled to a continuum description of oxygen transport. Measurements using high-resolution fMRI demonstrate the efficacy of the model. The model predicts substantial spatial variations of the oxygen saturation along the length of capillaries and veins, and fits the varied gamut of measured HRFs by the combined effects of corresponding CBF and CMRO2 responses. Three interesting relationships among the hemodynamic parameters are predicted. First, there is an offset linear correlation with approximately unity slope between CBF and CMRO2 responses. Second, the HRF undershoot is strongly correlated to the corresponding CBF undershoot. Third, late-time-CMRO2 response can contribute to a slow recovery to baseline, lengthening the HRF undershoot. The model provides a powerful mathematical framework to understand the dynamics of neurovascular and neurometabolic responses that form the BOLD HRF.
authors.affiliation: Department of Neuroscience, Core for Advanced MR Imaging, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Jung Hwan
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Neuroscience, Core for Advanced MR Imaging, Baylor College of Medicine, Houston, TX 77030, USA. Electronic address: ress@bcm.edu.
authors.forename: David
authors.initials: D
authors.lastname: Ress
mesh_terms: D001158:Arteries / Q000378:metabolism*; D001921:Brain / Q000098:blood supply* / Q000378:metabolism*; D001931:Brain Mapping; D006801:Humans; D008279:Magnetic Resonance Imaging; D008959:Models, Neurological; D000069336:Neurovascular Coupling; D010100:Oxygen / Q000378:metabolism; D010775:Photic Stimulation; D014796:Visual Perception / Q000502:physiology*
chemical_list: D010100:Oxygen
keywords: Cerebral blood flow; Cerebral hemodynamics; Computational model; Functional MRI (fMRI); Neurophysiology; Neurovascular coupling; Neurovascular unit