Transient BOLD responses at block transitions.

Block-design fMRI responses include sustained components present for the duration of each task block as well as transient components at the beginning and end of each block. Almost all prior block-design fMRI studies have focused on the sustained response components while the transient responses at block transitions have been largely ignored. These transients, therefore, remain poorly characterized. We here present a systematic study of block-transition transient responses obtained using four widely divergent tasks. We characterize transient response topography and examine the extent to which these responses vary across different tasks and between block onset and offset. Our analysis reveals that certain regions show transient responses regardless of task or transition type. However, our analysis also shows that specific task state transitions give rise to transient responses with unique spatial profiles. Relevance of the current findings to studies of exogenous attention, task shifting, and the BOLD overshoot is discussed.