To assess resting-state functional connectivity (rsFC) of the ipsilesional superior parietal lobule (SPL) and intraparietal sulcus (IPS) using functional magnetic resonance imaging (fMRI) in chronic stroke patients with hemiparesis both with and without post-stroke spasticity (PSS) and to explore the relationship between SPL/IPS resting-state functional connectivity (rsFC) and PSS severity.

Posts-stroke spasticity hampers effective rehabilitation of the paretic arm and lowers the quality of life. Effective PSS treatment with botulinum neurotoxin (BoNT) is associated with transient decrease in task-related fMRI activation of the ipsilesional SPL and IPS. We hypothesized that this would be reflected in changes in rsFC of the SPL/IPS.

Fourteen chronic stroke patients with upper limb weakness and PSS (the PSS group) and 8 patients with comparable weakness but no PSS (the control group) underwent clinical and spasticity evaluation and 3 fMRI examinations, at baseline (W0) and 4 and 11 weeks after BoNT (W4 and W11, respectively). Seed-based rsFC of the atlas-based SPL and IPS was evaluated using a group×time interaction analysis and the change in rsFC of SPL/IPS was correlated with change in PSS (modified Ashworth scale), integrity of the ipsilesional somatosensory afferent pathway (evoked potential N20 latency), and age.

In the PSS group, transient improvement in PSS was associated with increase in rsFC between the ipsilesional IPS and the contralesional SPL at W4. The interhemispheric connectivity was negatively correlated with PSS severity at baseline and with PSS improvement at W4. These changes in the posterior parietal interhemispheric rsFC suggest that previously observed task-related changes in SPL/IPS were independent of actual task performance.

We propose adaptation of the internal forward model as the possible underlying mechanism and discuss its potential association with increased limb use or improved motor performance, as well as its potential contribution to the clinical effects of BoNT.