# The structural reserve of brain networks influences outcomes after a stroke

## TL;DR

The structure of brain networks before a stroke can predict how well someone will recover afterward.

## Contribution

This study identifies pre-stroke brain network topology as a novel predictor of stroke recovery outcomes.

## Key findings

- Less segregated and more integrated brain networks are linked with better recovery outcomes.
- Network modularity consistently influences various recovery measures independently of initial deficit or age.
- Contralesional hemisphere network efficiency predicts long-term neurological and motor outcomes.

## Abstract

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.

Frontzkowski and Hunze et al. show that differences in brain network architecture influence stroke recovery. Patients with more efficient and less modular structural networks in the contralesional hemisphere experienced more favourable long-term outcomes, emphasizing the importance of brain network reserve as a critical determinant of recovery after stroke.

Graphical Abstract