title: An investigation of the impulse functions for the nonlinear BOLD response in functional MRI.
abstract: Functional MRI (fMRI) based on blood oxygenation level dependent (BOLD) contrast can be used to detect hemodynamic responses to a broad range of stimuli. It however remains unclear in what fashion the BOLD response is a linear system, and how the impulse function differs with stimulation of varying duration. To address this question, fMRI using visual stimulation with a wide range of duration (0.5-12 s) was performed in six human volunteers. A strong linear correlation was shown on the full width at half maximum (r = 0.998) of the BOLD response curves and the area under the curves (r = 0.999) to the duration of stimulation. However, comparing the errors of the measured and predicted response curves, our results showed a poorer linearity at stimuli of shorter duration. By examining the impulse functions derived from different stimuli, based on the assumption that a linear convolution relationship existed, a higher differentiation was shown in the experiments with shorter stimuli (<3 s). Compared to the area under the impulse function derived from 12 s stimulation, with that obtained from 0.5, 1, 2, 3, 4, 8 s stimuli resulted in differences of 66.2, 33.5, 15.1, 5.4, 0.9, 7.9%, respectively. This study suggests a higher degree of nonlinearity in the BOLD signal changes due to stimuli of shorter duration, in agreement with earlier work.
authors: Research Imaging Center, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78284-6240, USA. gao@uthscsa.edu
authors: H
authors: H
authors: Liu
authors: J
authors: J
authors: Gao
mesh_terms: D001921:Brain / Q000502:physiology; D001931:Brain Mapping; D003627:Data Interpretation, Statistical; D005074:Evoked Potentials, Visual / Q000502:physiology; D006439:Hemodynamics; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008959:Models, Neurological; D017711:Nonlinear Dynamics; D010100:Oxygen / Q000097:blood*; D010775:Photic Stimulation; D013997:Time Factors; D014793:Visual Cortex / Q000502:physiology*
chemical_list: D010100:Oxygen