Greater scaling and less flexible timing of cortical responses during challenging reactive balance after stroke
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Background
Cortical N1 responses to balance perturbations are larger and earlier with increasing magnitude and differ with reactive stepping. Whether stroke alters this modulation is unknown.
Objective
To compare N1 modulation across perturbation magnitudes and reactive balance outcomes in older adults with and without stroke. We hypothesized that people with stroke would show greater N1 scaling than controls; that larger N1s at small perturbations would limit scaling (a recruitment ceiling); and that stroke would constrain N1 modulation by stepping outcome.
Methods
Sixteen people with chronic stroke (66±11 years) and 15 age-similar controls (68±8 years) received forward support-surface perturbations at a small standardized magnitude and at individual step thresholds (∼50% unintentional steps). N1 peak amplitude and latency were compared across magnitudes in feet-in-place trials, and between stepping and feet-in-place trials at step threshold. N1 scaling was the relative amplitude increase between magnitudes.
Results
Despite lower clinical balance after stroke (p<0.001), step thresholds were similar between groups. N1s were larger with shorter latencies at step threshold in both groups (p<0.001), but scaled more after stroke (44% vs 13%,p=0.009). Greater scaling was associated with smaller small-magnitude N1s after stroke (β=−0.43, p=0.041) and higher step thresholds across groups (β=0.35, p=0.048). N1 latency was 11 ms longer in stepping trials in controls but not after stroke (interaction p=0.024).
Conclusions
Scaling of cortical recruitment with increasing perturbation magnitude may support reactive balance, and may be an adaptive mechanism for people after stroke. Less flexible N1 timing after stroke may limit cortical tuning to balance recovery strategy.
