Reticulospinal hyperexcitability after stroke: Associations with impairment severity and no evidence of functional advantage in severe cases

OBJECTIVE: Reticulospinal tract (RST) excitability increases after stroke. Although animal studies suggest that this hyperexcitability may compensate for corticospinal tract damage, its role in motor function in persons with stroke (PwS) remains debated. This study aimed to replicate RST hyperexcitability in PwS using the StartReact paradigm, examine associations with motor impairment, and explore whether heightened responses were associated with functional benefit in a subgroup with severe upper-limb impairment. METHODS: In this cross-sectional study, 46 PwS and 37 healthy controls completed a StartReact paradigm. Upper-limb impairment was assessed using the Upper Extremity Fugl-Meyer, Action Research Arm Test (ARAT), grip strength, and Modified Ashworth Scale. PwS were classified as having high or typical StartReact effects based on the control 90th percentile. Severe impairment was defined as ARAT ≤10. RESULTS: PwS showed greater StartReact effects than controls (median: 15.00 vs. 5.21 ms; U = 667.5, p = 0.047, rank-biserial correlation = 0.22). StartReact effects were negatively correlated with ARAT (r = -0.44, p < 0.01), Fugl-Meyer (r = -0.51, p < 0.01), and grip strength (r = -0.36, p = 0.01). The high StartReact subgroup showed poorer upper-limb function, weaker grip strength, and greater biceps spasticity (U = 266, p = 0.02). Within the severe impairment subgroup, high StartReact effects were not associated with greater grip strength. CONCLUSIONS: StartReact-derived RST hyperexcitability was associated with greater post-stroke upper-limb motor impairment. In the severe subgroup, heightened responses were not associated with greater grip strength. These findings cannot establish that RST hyperexcitability supports functional recovery.