Longitudinal changes of motor cortical excitability and transcallosal inhibition after subcortical stroke

• Continuing clinical improvement was observed over a 1-year period following subcortical stroke.
• Overall excitability in the unaffected hemisphere was increased at the post-acute period following stroke, which may have resulted in enhanced transcallosal inhibition to the affected hemisphere.
• It is unclear whether there was a causal relationship between the enhanced transcallosal inhibition and the extent of clinical recovery.

ObjectiveA general lack of longitudinal studies on interhemispheric interactions following stroke led us to use transcranial magnetic stimulation (TMS) to examine changes in corticospinal/intracortical excitability and transcallosal inhibition over a 1-year period following subcortical stroke.MethodsWe measured TMS parameters such as motor threshold (MT), short-interval intracortical inhibition (SICI), and ipsilateral silent period (iSP) and evaluated clinical scores at three time-points (T1, T2, and T3) in 24 patients and 25 age-matched healthy subjects.ResultsAt T1, we observed reduced MTs and SICIs with prolonged iSPs in the unaffected hemisphere (UH). In contrast, increased MTs and reduced SICIs were observed in the affected hemisphere (AH). These abnormalities gradually reduced and no MEP response to TMS at T1 predicted a worse prognosis. The prolonged iSP at T1 was associated with more severe impairments, but it did not necessarily predict a worse prognosis after 1 year.ConclusionsUH excitability was increased at the post-acute time-period, which may have resulted in enhanced transcallosal inhibition to the AH. However, it is unclear whether there was a causal relationship between the enhanced transcallosal inhibition and the extent of clinical recovery.SignificanceThis is the first study to demonstrate changes in transcallosal inhibition over a longitudinal period following stroke.