The structural reserve of brain networks influences outcomes after a stroke

Structural brain reserve capacity has recently gained an increasing interest in stroke recovery research. Focal and global measures of brain reserve have been linked with recovery trajectories. Whether the reserve localized within large-scale brain networks might also carry information to better understand outcome variability after stroke is an open question. This work analysed 31 patients with severe, first-ever unilateral, supratentorial stroke. Patients underwent MRI brain imaging and clinical testing within the first 2 weeks after the event and a longitudinal clinical follow-up after 3-6 months. Individual tractography in the contralesional hemisphere was performed to reconstruct structural connectomes to approximate the state of the ipsilesional brain networks before the stroke. Graph theory was applied to describe network integration and segregation topologies. Linear and ordinal logistic regression analyses were conducted to associate network topologies at baseline with neurological symptom burden, global and activity-related disability and motor impairment at follow-up. The main finding was that less segregated and more integrated networks, characterized by lower network modularity and higher efficiency, were linked with a more favourable outcome on follow-up. Modularity exerted a remarkably consistent influence across various outcome measures. This association was independent of the initial deficit, lesion volume or age. This study sheds novel light on brain reserve, localizing within the topology of pre-stroke structural brain networks, as a critical determinant of recovery after stroke.