Mapping white-matter functional organization at rest and during naturalistic visual perception

- ICA applied to white-matter fMRI signals reveals reproducible and hierarchical patterns.
- White-matter ICA components are mostly preserved, but are in part distinct between the resting state and the task state.
- The distinction is specific to the axonal fibers involved in the task execution.
- White-matter fMRI data are not noise or artifacts, but instead are signals of likely neuronal origin.

Despite the wide applications of functional magnetic resonance imaging (fMRI) to mapping brain activation and connectivity in cortical gray matter, it has rarely been utilized to study white-matter functions. In this study, we investigated the spatiotemporal characteristics of fMRI data within the white matter acquired from humans both in the resting state and while watching a naturalistic movie. By using independent component analysis and hierarchical clustering, resting-state fMRI data in the white matter were de-noised and decomposed into spatially independent components, which were further assembled into hierarchically organized axonal fiber bundles. Interestingly, such components were partly reorganized during natural vision. Relative to resting state, the visual task specifically induced a stronger degree of temporal coherence within the optic radiations, as well as significant correlations between the optic radiations and multiple cortical visual networks. Therefore, fMRI contains rich functional information about the activity and connectivity within white matter at rest and during tasks, challenging the conventional practice of taking white-matter signals as noise or artifacts.