Heightened Reticulospinal Excitability after Severe Corticospinal Damage in Chronic Stroke

Area of Science:

• Neuroscience
• Rehabilitation Medicine
• Motor Control

Background:

• Stroke frequently causes corticospinal tract (CST) damage, leading to motor deficits.
• Proximal motor recovery after severe CST damage suggests involvement of alternative motor pathways.
• The reticulospinal tract (RST) is a potential compensatory pathway for CST loss.

Purpose of the Study:

• To investigate RST excitability modulation after stroke.
• To determine the relationship between RST excitability and CST damage severity.
• To understand RST's role in motor recovery post-stroke.

Main Methods:

• Utilized a novel startle-conditioned transcranial magnetic stimulation (TMS) paradigm.
• Measured ipsilateral motor evoked potentials (iMEPs) as an index of RST excitability.
• Studied 22 chronic stroke participants (mild to severe CST damage) and 14 controls.

Main Results:

• Higher iMEP presence in the paretic arm of individuals with severe CST damage.
• iMEP presence was significantly higher compared to non-paretic arms, mild CST damage, and controls.
• iMEP presence correlated positively with motor impairment severity across the stroke cohort.

Conclusions:

• Upregulated RST activity may compensate for CST damage, facilitating some proximal motor recovery.
• Deficits in out-of-synergy movements and finger fractionation persist despite RST compensation.
• Modulating RST activity could offer therapeutic benefits or detriments depending on pathway reliance.