Bilateral functional connectivity at rest predicts apraxic symptoms after left hemisphere stroke.

Abstract

Increasing evidence indicates that focal lesions following stroke cause alterations in connectivity among functional brain networks. Functional connectivity between hemispheres has been shown to be particularly critical for predicting stroke-related behavioral deficits and recovery of motor function and attention. Much less is known, however, about the relevance of interhemispheric functional connectivity for cognitive abilities like praxis that rely on strongly lateralized brain networks. In the current study, we examine correlations between symptoms of apraxia—a disorder of skilled action that cannot be attributed to lower-level sensory or motor impairments—and spontaneous, resting brain activity in functional MRI in chronic left hemisphere stroke patients and neurologically-intact control participants. Using a data-driven approach, we identified 32 regions-of-interest in which pairwise functional connectivity correlated with two distinct measures of apraxia, even when controlling for age, head motion, lesion volume, and other artifacts: overall ability to pantomime the typical use of a tool, and disproportionate difficulty pantomiming the use of tools associated with different, competing use and grasp-to-move actions (e.g., setting a kitchen timer versus picking it up). Better performance on both measures correlated with stronger interhemispheric functional connectivity. Relevant regions in the right hemisphere were often homologous to left hemisphere areas associated with tool use and action. Additionally, relative to overall pantomime accuracy, disproportionate difficulty pantomiming the use of tools associated with competing use and grasp actions was associated with weakened functional connectivity among a more strongly left-lateralized and peri-Sylvian set of brain regions. Finally, patient performance on both measures of apraxia was best predicted by a model that incorporated information about lesion location and functional connectivity, and functional connectivity continued to explain unique variance in behavior even after accounting for lesion loci. These results indicate that interhemispheric functional connectivity is relevant even for a strongly lateralized cognitive ability like praxis and emphasize the importance of the right hemisphere in skilled action.