Limited capacity for ipsilateral secondary motor areas to support hand function post-stroke

Area of Science:

• Neuroscience
• Motor Control
• Stroke Rehabilitation

Background:

• Ipsilateral cortico-reticulospinal tract (CRST) from secondary motor areas innervates proximal and distal arm muscles.
• CRST is proposed as a potential backup system for hand function post-stroke due to its intact ipsilateral pathways.

Purpose of the Study:

• To investigate the role of ipsilateral secondary motor areas in hand function after stroke.
• To determine if ipsilateral CRST can adequately support distal hand movements post-stroke.

Main Methods:

• Combined magnetic resonance imaging (MRI), high-density electroencephalography (EEG), and robotics.
• Assessed structural morphometry of the sensorimotor cortex in 17 stroke survivors and 12 controls.
• Measured cortical activity during hand opening tasks under different load conditions.

Main Results:

• Stroke survivors showed increased grey matter density in ipsilateral secondary motor areas compared to controls.
• Increased reliance on ipsilateral secondary motor areas during hand opening was observed in stroke survivors, especially under load.
• This increased activation correlated with decreased hand opening ability and involuntary coupling between shoulder abduction and finger flexion.

Conclusions:

• Ipsilateral secondary motor areas may support proximal arm movements post-stroke.
• These pathways lack the capacity for fine motor control required for distal hand function, such as hand opening.
• The findings suggest that ipsilateral CRST is insufficient for restoring hand function after stroke.