Ipsilateral motor pathways after stroke: implications for non-invasive brain stimulation

Area of Science:

• Neuroscience
• Rehabilitation Medicine
• Motor Control

Background:

• The two cerebral hemispheres play critical roles in controlling the upper limb in humans.
• Stroke often impairs upper limb function, necessitating effective rehabilitation strategies.
• Non-invasive brain stimulation (NBS) is explored for stroke recovery, typically targeting the primary motor cortex (M1).

Purpose of the Study:

• To highlight the significance of ipsilateral descending pathways in functional recovery post-stroke.
• To examine the implications of contralesional primary motor cortex (M1) suppression via NBS.
• To propose a neurophysiological model for ipsilesional arm control via the cortico-reticulo-propriospinal pathway (CRPP).

Main Methods:

• Review of neurophysiological models concerning ipsilateral descending pathways.
• Discussion of the cortico-reticulo-propriospinal pathway (CRPP) as a potential control mechanism.
• Consideration of neurophysiological, neuroimaging, and clinical assessments for treatment decisions.

Main Results:

• Contralesional M1 suppression via NBS may inadvertently reduce the excitability of crucial ipsilateral descending pathways.
• The cortico-reticulo-propriospinal pathway (CRPP) represents a significant ipsilateral pathway for paretic upper limb control.
• The effectiveness of NBS protocols must be individualized based on the patient's specific neurophysiological profile.

Conclusions:

• The role of the CRPP in motor control for individual stroke patients needs careful consideration before applying NBS.
• Suppression of contralesional M1 may not always be beneficial and could impede recovery via ipsilateral pathways.
• Integrating various assessment methods can guide the clinical application of NBS for optimizing stroke rehabilitation.