Paretic Hand Beta Band Intermuscular Coherence Increases Following non-Paretic Hand Exercise to Task-Failure in Chronic Stroke.

Abstract

Intermuscular coherence (IMC), especially in the beta band, has been widely used as a non-invasive approach to estimate the strength of corticospinal connectivity. The corticospinal tract is frequently damaged as a result of stroke, which may impair the strength of corticospinal connectivity, particularly that contributing to manual dexterity. Here we investigated acute adaptations in IMC and manual dexterity in fifteen chronic stroke survivors and seven age-matched healthy controls who performed exercise to task-failure with their non-paretic hand (or dominant hand for healthy controls). Dexterity (measured by Box-and-Blocks Test, BBT) and IMC were tested at baseline, following exercise to task-failure, and every 45 min until 4 h after task-failure (7 times in total). At baseline, paretic hand beta and gamma band IMC were significantly reduced in stroke survivors (P's = 0.006). Additionally, at baseline paretic hand (or non-dominant hand for healthy controls) BBT performance and gamma band IMC revealed significant positive correlations in both stroke survivors (R² = 0.40, P = 0.010) and the whole sample (R² = 0.33, P = 0.005). Paretic hand BBT performance increased immediately and at 225 min after task-failure compared with baseline (P's = 0.017 and 0.014, respectively). Paretic hand beta band IMC increased immediately and remained significantly elevated at 45 min after task-failure (P = 0.045 and 0.005, respectively) while paretic hand gamma band IMC was increased at 135 min after task-failure (P = 0.051). Taken together, our results suggest increased strength of corticospinal connectivity to the paretic hand as an acute adaptation to non-paretic hand exercise to task-failure. Concurrent facilitation of paretic hand manual dexterity and strengthened ipsilesional corticospinal connectivity suggests this approach should be explored as a strategy to promote recovery of corticospinal connectivity and paretic hand motor function in neurorehabilitation.