Bayesian technique for investigating linearity in event-related BOLD fMRI

Event-related BOLD fMRI data is modeled as a linear time-invariant system. Together with Bayesian inference techniques, a statistical test is develope d for rigorously detecting linearity/ nonlinearity in the BOLD response sys tem. The test is applied to data collected from eight subjects using an eve nt-related paradigm with a switching checkerboard as the visual stimulus. A nalyzed as a group, the results clearly find the response to be nonlinear. When each subject is analyzed individually, however, the results are predom inantly nonlinear, but there is some evidence to suggest that there may be a crossover from a linear to a nonlinear regime and vice versa, This could be important when estimating physiological parameters for individuals. Addi tionally, estimates of the hemodynamic response function and corresponding response were obtained, but there was no consistent appearance of a poststi mulus undershoot in the event-related BOLD response. (C) 2001 Wiley-Liss, I nc.