State-dependent interhemispheric inhibition reveals individual differences in motor behavior in chronic stroke

Objective: To investigate state-dependent interhemispheric inhibition (IHI) in chronic stroke survivors compared to neurotypical older adult controls, and test whether abnormal IHI modulation was associated with upper extremity motor behavior.Methods: Dual-coil transcranial magnetic stimulation (TMS) measured IHI bi-directionally, between non-lesioned and lesioned motor cortex (M1) in two activity states: (1) at rest and (2) during contralateral isometric hand muscle contraction. IHI was tested by delivering a conditioning stimulus 8-msec or 50-msec prior to a test stimulus over contralateral M1. Paretic motor behavior was assessed by clinical mea-sures of impairment, strength, and dexterity, and mirroring activity in the non-paretic hand.Results: Stroke survivors demonstrated reduced IHI at rest, and less IHI modulation (active - rest) com-pared to controls. Individual differences in IHI modulation were related to motor behavior differences where greater IHI modulation was associated with greater motor impairment and more mirroring. In contrast, there were no relationships between IHI at rest and motor behavior.Conclusions: Abnormal state-dependent interhemispheric circuit activity may be more sensitive to post -stroke motor deficits than when assessed in a single motor state. Significance: Characterizing state-dependent changes in neural circuitry may enhance models of stroke recovery and inform rehabilitation interventions.(c) 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

Automated summary

This study aimed to investigate state-dependent interhemispheric inhibition (IHI) in chronic stroke survivors compared to neurotypical older adult controls and examined its association with upper extremity motor behavior. The results showed that stroke survivors had reduced IHI at rest and less modulation of IHI during activity compared to controls. Individual differences in IHI modulation were related to motor behavior differences, where greater modulation was associated with greater motor impairment and more mirroring. The findings suggest that abnormal state-dependent interhemispheric circuit activity may be more sensitive to post-stroke motor deficits. Characterizing state-dependent changes in neural circuitry could enhance stroke recovery models and inform rehabilitation interventions.