Exploring spatiotemporal network transitions in task functional MRI

Abstract

A critical question for cognitive neuroscience regards how transitions between cognitive states emerge from the dynamic activity of functional brain networks. However, current methodologies cannot easily evaluate both the spatial and temporal changes in brain networks with cognitive state. Here we combine a simple data reorganization with spatial ICA, enabling a spatiotemporal ICA (stICA) which captures the consistent evolution of networks during onset and offset of a task. The technique was applied to FMRI datasets involving alternating between rest and task and to simple synthetic data. Starting and finishing time-points of periods of interest (anchors) were defined at task block onsets and offsets. For each subject, the ten volumes following each anchor were extracted and concatenated spatially, producing a single 3D sample. Samples for all anchors and subjects were concatenated along the fourth dimension. This 4D dataset was decomposed using ICA into spatiotemporal components. One component exhibited the transition with task onset from a default mode network (DMN) becoming less active to a fronto-parietal control network (FPCN) becoming more active. We observed other changes with relevance to understanding network dynamics, e.g., the DMN showed a changing spatial distribution, shifting to an anterior/superior pattern of deactivation during task from a posterior/inferior pattern during rest. By anchoring analyses to periods associated with the onsets and offsets of task, our approach reveals novel aspects of the dynamics of network activity accompanying these transitions. Importantly, these findings were observed without specifying a priori either the spatial networks or the task time courses.