Long-lasting TMS motor threshold elevation in mild traumatic brain injury

Area of Science:

• Neuroscience
• Neurology
• Traumatology

Background:

• Mild traumatic brain injury (mTBI) frequently results in persistent symptoms.
• These symptoms may stem from diffuse neuronal damage impacting cortical excitability.
• Motor threshold (MT), assessed via transcranial magnetic stimulation (TMS), reflects cortical excitability and corticospinal tract integrity.

Purpose of the Study:

• To investigate cortical excitability in individuals with a history of mild traumatic brain injury (mTBI).
• To determine if motor threshold (MT) differs between mTBI patients (symptomatic and recovered) and healthy controls.
• To explore potential long-term neurological consequences of mTBI.

Main Methods:

• Navigated transcranial magnetic stimulation (nTMS) and electromyography were employed to measure left hemisphere MTs.
• Nineteen subjects with mTBI (11 symptomatic, 8 recovered) and 9 healthy controls participated.
• All participants had normal brain MRIs and were not on centrally acting medication; injuries occurred approximately 5 years prior.

Main Results:

• The mean MT was significantly higher in mTBI subjects (53.4%) compared to healthy controls (43.0%).
• No correlation was found between subjective recovery status and measured MT.
• These findings indicate chronic alterations in cortical excitability following mTBI.

Conclusions:

• Chronic elevation of MT suggests that mTBI may lead to compensated, yet not fully recovered, neurological states years post-injury.
• Possible underlying mechanisms include decreased cortical excitability or impaired subcortical conduction.
• Further research is needed to elucidate the precise causes of MT elevation in mTBI populations.