Delayed Cortical Responses During Reactive Balance After Stroke Associated With Slower Kinetics and Clinical Balance Dysfunction.

Background: Slowed balance and mobility after stroke have been well-characterized. Yet the effects of unilateral cortical lesions on whole-body neuromechanical control is poorly understood, despite increased reliance on cortical resources for balance and mobility with aging. Objective. We tested whether individuals post stroke show impaired cortical responses evoked during reactive balance, and the effect of asymmetrical interlimb contributions to balance recovery and the evoked cortical response.

Methods: Using electroencephalography, we assessed cortical N1 responses evoked over fronto-midline regions (Cz) during backward support-surface perturbations loading both legs and posterior-lateral directions that preferentially load the paretic or nonparetic leg in individuals' post-stroke and age-matched controls. We tested relationships between cortical responses and clinical balance/mobility function, as well as to center of pressure (CoP) rate of rise (RoR) during balance recovery.

Results: Cortical N1 responses were smaller and delayed after stroke (P < .047), regardless of perturbation condition. In contrast to controls, slower cortical response latencies associated with lower clinical function in stroke (Mini Balance Evaluation Systems Test: r = -.61, P = .007; Timed-Up-and-Go: r = .53, P = .024; walking speed: r = -.46, P = .055). Paretic-loaded balance recovery revealed slower CoP RoR (P = .012) that was associated with delayed cortical response latencies (r = -.70, P = .003); these relationships were not present during bilateral and nonparetic-loaded conditions, nor in the older adults control group.

Conclusions: Individuals after stroke may be limited in their balance ability by the slowed speed of their cortical responses to destabilization. In particular, paretic leg loading may reveal cortical response impairments that reflect reduced paretic motor capacity.