Low frequency repetitive transcranial magnetic stimulation to the non-lesioned hemisphere improves paretic arm reach-to-grasp performance after chronic stroke

Purpose: To investigate the effect of inhibitory low frequency repetitive Transcranial Magnetic Stimulation (rTMS) applied to the non-lesioned hemisphere on kinematics and coordination of paretic arm reach-to-grasp (RTG) actions in individuals with stroke. Relevance: This study is designed as a phase I trial to determine the feasibility and efficacy of low frequency rTMS applied to the non-lesioned hemisphere for the recovery of reach-to-grasp actions in individuals with hemiparesis secondary to stroke. The results have important implications for the use of rTMS in parallel with complex paretic arm skill practice. Participants: Nine adults, anterior circulation unilateral stroke. Their average age was 59 years, the average time since stroke was 4.8 years. Method and analysis: Two TMS treatments were performed on two separate days: active rTMS and sham rTMS. Cortico-motor excitability (CE) of the non-lesioned hemisphere as well as RTG kinematics of the paretic hand as participants reached for a dowel of 1.2 cm in diameter was assessed before and after the rTMS treatments. In the active condition, rTMS was applied over the "hot spot" of the extensor digitorum communis muscle (EDC) in primary motor cortex (M1) of the non-lesioned hemisphere at 90% resting motor threshold. TMS pulses were delivered at 1 Hz for 20 min. In the sham condition, a sham coil was positioned similar to the active condition; TMS clicking noise was produced but no TMS pulse was delivered. Dependent measures: CE was measured as peak-to-peak amplitude of the motor evoked potential at 120% of resting motor threshold. RTG kinematics included movement time, peak transport velocity, peak aperture, time of peak transport velocity and time of peak aperture. RTG coordination was captured by cross correlation coefficient between transport velocity and grasp aperture size. Results: While 1 Hz rTMS applied over non-lesioned M1 significantly decreased the MEP amplitude of non-paretic EDC, sham TMS did not have a significant effect on MEP amplitude. Active rTMS significantly decreased total movement time and increased peak grasp aperture. There were no changes in peak transport velocity or the time of peak transport velocity or the time of peak aperture after application of active rTMS. Additionally, the participants completed RTG actions with a more coordinated pattern after undergoing active rTMS. Following sham TMS, there were no changes in CE, RTG kinematics or coordination. While there were no significant correlation between changes in cortico-motor excitability and RTG kinematics, the decrease in cortico-motor excitability of the non-lesioned hemisphere showed a strong correlation with an increase in cross-correlation coefficient. Conclusions and implications: The findings demonstrate the feasibility and efficacy of low frequency rTMS applied to the non-lesioned hemisphere for the recovery of reach-to-grasp actions in individuals with hemiparesis secondary to stroke. The inhibitory effect of low frequency rTMS resulted in improved paretic hand reach-to-grasp performance with faster movement time and more coordinated reach-to-grasp pattern. These results have important implications for the use of rTMS for stroke rehabilitation.