Revisiting interhemispheric imbalance in chronic stroke: A tDCS study

Area of Science:

• Neuroscience
• Rehabilitation Medicine
• Neurology

Background:

• Chronic stroke patients with moderate-to-severe motor impairment often exhibit altered motor control strategies.
• There is a potential reliance on contralesional motor areas for controlling the paretic limb in these patients.

Purpose of the Study:

• To investigate if enhancing contralesional motor cortex excitability using anodal transcranial direct current stimulation (a-tDCS) can improve motor performance.
• To assess the effects of a-tDCS on motor function in chronic stroke patients with moderate-to-severe impairment.

Main Methods:

• Ten chronic stroke patients with moderate-to-severe motor impairment participated.
• Participants received a-tDCS, cathodal tDCS (c-tDCS), and sham stimulation targeting the contralesional motor cortex (M1).
• Motor performance, corticospinal excitability, corticospinal tract integrity, and basal GABA concentration were assessed.

Main Results:

• Anodal tDCS significantly increased contralesional corticomotor excitability.
• Cathodal tDCS did not significantly alter corticomotor excitability.
• The impact of tDCS on motor performance was negatively correlated with ipsilesional GABA concentration following c-tDCS.

Conclusions:

• Anodal tDCS effectively modulates contralesional motor cortex excitability in chronic stroke patients.
• Further research into non-invasive brain stimulation protocols, like a-tDCS, is needed to facilitate contralesional M1 function.
• The findings suggest the inter-hemispheric imbalance model may require re-evaluation for patients with more severe stroke impairments.