Late responses after transcranial magnetic stimulation in stroke

Area of Science:

• Neuroscience
• Neurology
• Rehabilitation Medicine

Background:

• Transcranial magnetic stimulation (TMS) elicits early Motor Evoked Potentials (MEPs).
• Late TMS responses, including the S > 150 response (150-300 ms post-stimulus), have been reported but are less understood.
• Investigating these late responses may offer new insights into brain function after injury.

Purpose of the Study:

• To longitudinally monitor the late S > 150 response in stroke patients.
• To assess the predictive value of the S > 150 response for clinical deficit improvement.
• To compare the sensitivity of late S > 150 responses and early MEPs to hemispheric lesions.

Main Methods:

• Longitudinal monitoring of the S > 150 response in 19 stroke patients with verified hemispheric ischemic lesions.
• Recording of early Motor Evoked Potentials (MEPs) for comparison.
• Correlation analysis between the presence/absence of S > 150 response and clinical improvement.

Main Results:

• The presence of the late S > 150 response on the first day post-stroke predicted excellent clinical deficit improvement.
• The S > 150 response demonstrated higher sensitivity to hemispheric lesions compared to early MEPs.
• Supratentorial structures, particularly cortical areas, are implicated in the generation of the S > 150 response.

Conclusions:

• The late S > 150 response is a sensitive indicator of hemispheric lesions and a predictor of good recovery in stroke patients.
• Recording late TMS responses can complement early MEP recordings for comprehensive stroke assessment.
• The findings support the hypothesis that cortical structures play a significant role in the S > 150 response.