title: Hemodynamic nonlinearities affect BOLD fMRI response timing and amplitude.
abstract: The interpretation of functional magnetic resonance imaging (fMRI) studies based on blood oxygen-level dependent (BOLD) contrast generally relies on the assumption of a linear relationship between evoked neuronal activity and fMRI response. While nonlinearities in this relationship have been suggested by a number of studies, it remains unclear to what extent they relate to the neurovascular response and are therefore inherent to BOLD fMRI. Full characterization of potential vascular nonlinearities is required for accurate inferences about the neuronal system under study. To investigate the extent of vascular nonlinearities, evoked activity was studied in humans with BOLD fMRI (n=28) and magnetoencephalography (MEG) (n=5). Brief (600-800 ms) rapidly repeated (1 Hz) visual stimuli were delivered using a stimulation paradigm that minimized neuronal nonlinearities. Nevertheless, BOLD fMRI experiments showed substantial remaining nonlinearities. The smallest stimulus separation (200-400 ms) resulted in significant response broadening (15-20% amplitude decrease; 10-12% latency increase; 6-14% duration increase) with respect to a linear prediction. The substantial slowing and widening of the response in the presence of preceding stimuli suggest a vascular rather than neuronal origin to the observed nonlinearity. This was confirmed by the MEG data, which showed no significant neuro-electric nonlinear interactions between stimuli as little as 200 ms apart. The presence of substantial vascular nonlinearities has important implications for rapid event-related studies by fMRI and other imaging modalities that infer neuronal activity from hemodynamic parameters.
authors.affiliation: Advanced MRI Section, LFMI, NINDS, NIH National Institutes of Health, Bethesda, MD 20892-1065, USA. Jacco.deZwart@nih.gov
authors.forename: Jacco A
authors.initials: JA
authors.lastname: de Zwart
authors.forename: Peter
authors.initials: P
authors.lastname: van Gelderen
authors.forename: J Martijn
authors.initials: JM
authors.lastname: Jansma
authors.forename: Masaki
authors.initials: M
authors.lastname: Fukunaga
authors.forename: Marta
authors.initials: M
authors.lastname: Bianciardi
authors.forename: Jeff H
authors.initials: JH
authors.lastname: Duyn
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000098:blood supply / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005071:Evoked Potentials / Q000502:physiology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D017711:Nonlinear Dynamics; D010100:Oxygen / Q000097:blood*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D010100:Oxygen