Can TMS based neurophysiology inform the delivery of rTMS after stroke?

Abstract

Transcranial magnetic stimulation (TMS) can be used to assess and alter cortical excitability in healthy and clinical populations. Studies using TMS demonstrate altered brain excitability and connectivity in both hemispheres during after stroke. Interhemispheric imbalance is noted after stroke such that the ipsilesional hemisphere shows less corticospinal excitability with smaller, or even absent, motor evoked potentials (MEPs). In contrast, the contralesional hemisphere often demonstrates equal or abnormally increased corticospinal excitability. Along with this imbalance, there can be altered in connectivity between the two hemispheres, often referred to as interhemispheric inhibition (IHI). After stroke, asymmetry in the level of IHI between the two hemispheres can be associated with functional recovery, although stroke severity may alter these relationships. Repetitive TMS (rTMS) alters local cortical excitability and counter interhemispheric imbalance after stroke. Yet, response to this intervention is highly variable with some stroke patients showing benefit while others do not.