Event-related analysis for event types of fixed order and restricted spacing by temporal quantification of trial-averaged MRI time courses

Purpose: To develop a method for event-related fMRI that allows rapidly presented event sequences to be analyzed, without requiring transitions of different event-types to be counterbalanced. Materials and Methods: A cued task switching procedure was investigated with an experimental trial comprising a visual task cue that indicated how,to process a subsequent visual target stimulus. Cue and target were either presented quasi-simultaneously, separated by a 100 msec cue-target-interval (CTI100), or the target presentation was delayed by 2000 msec (CTI2000). To characterize the trial-related BOLD-response in terms of its temporal relation to the underlying event structure, the pattern of onset latency differences and peak latency differences for CTI2000 minus en 100 was evaluated. Independent estimates of onset latencies and peak latencies were determined for preprocessed trial-averaged time courses by jackknife resampling. Results: Validating results were obtained for two brain areas with known characteristics: the visual cortex (cue-locked plus target-locked activation) and the motor cortex (response-locked activation). Extending the analysis to prefrontal areas with a priori unknown characteristics differentiated between several meaningful temporal activation patterns. Conclusion: The method yielded a fine-grained temporal description of trial-related BOLD-responses that could be successfully used for the event-related analysis of an experimental design that was highly restricted with respect to event order and event spacing.