  Cognitive flexibility describes the human ability to switch between modes of
mental function to achieve goals. Mental switching is accompanied by transient
changes in brain activity, which must occur atop an anatomical architecture
that bridges disparate cortical and subcortical regions by underlying white
matter tracts. However, an integrated perspective regarding how white matter
networks might constrain brain dynamics during cognitive processes requiring
flexibility has remained elusive. To address this challenge, we applied
emerging tools from graph signal processing to decompose BOLD signals based on
diffusion imaging tractography in 28 individuals performing a perceptual task
that probed cognitive flexibility. We found that the alignment between
functional signals and the architecture of the underlying white matter network
was associated with greater cognitive flexibility across subjects. Signals with
behaviorally-relevant alignment were concentrated in the basal ganglia and
anterior cingulate cortex, consistent with cortico-striatal mechanisms of
cognitive flexibility. Importantly, these findings are not accessible to
unimodal analyses of functional or anatomical neuroimaging alone. Instead, by
taking a generalizable and concise reduction of multimodal neuroimaging data,
we uncover an integrated structure-function driver of human behavior.
