title: Separating processes within a trial in event-related functional MRI I. The Method.
abstract: Many behavioral paradigms involve temporally overlapping sensory, cognitive, and motor components within a single trial. The complex interplay among these factors makes it desirable to separate the components of the total response without assumptions about shape of the underlying hemodynamic response. We present a method that does this. Four conditions were studied in four subjects to validate the method. Two conditions involved rapid event-related studies, one with a low-contrast (5%) flickering checkerboard and another with a high-contrast (95%) checkerboard. In the third condition, the same high-contrast checkerboard was presented with widely spaced trials. Finally, multicomponent trials were formed from temporally adjacent low-contrast and high-contrast stimuli. These trials were presented as a rapid event-related study. Low-contrast stimuli presented in isolation (partial trials) made it possible to uniquely estimate both the low-contrast and high-contrast responses. These estimated responses matched those measured in the first three conditions, thereby validating the method. Nonlinear interactions between adjacent low-contrast and high-contrast responses were shown to be significant but weak in two of the four subjects.
authors.affiliation: Department of Radiology, Washington University, St. Louis, Missouri, 63110, USA. jmo@npg.wustl.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Ollinger
authors.forename: G L
authors.initials: GL
authors.lastname: Shulman
authors.forename: M
authors.initials: M
authors.lastname: Corbetta
mesh_terms: D000465:Algorithms; D005071:Evoked Potentials / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008959:Models, Neurological; D013997:Time Factors