Homosynaptic Depression of the Soleus Predicts Post-Stroke Gait Speed

Homosynaptic depression (HD) refers to the reduction in the magnitude of the monosynaptic spinal reflex resulting from prior activation of the circuit, often evoked with the H-reflex. Previous literature has reported HD of the soleus H-reflex is reduced post-stroke. However, it remains unclear if HD plays a role in functional impairments. The goal of this study was to characterize HD of the soleus H-reflex in individuals with post-stroke gait impairments and examine the relationship with functional measures of gait. Our results revealed that individuals after stroke experienced reduced depression at longer (8s) interstimulus intervals compared to age-matched neurologically intact individuals. However, we did not observe a difference in the change in HD across interstimulus intervals between groups, contrary to previous reports. This finding could not be explained by age of participants. In addition, we found a strong correlation between faster gait speed and reduced change in depression in individuals after stroke. While the underlying mechanisms linking HD with gait are unclear, this finding represents the first piece of evidence of the potential role of HD in function. Further research is needed to understand the parameters that guide HD and clarify how useful the mechanism is for improving the assessment and treatment of post-stroke impairments.