Functional and structural cortical characteristics after restricted focal motor cortical infarction evaluated at chronic stage – Indications from a preliminary study

• TMS and DWI show changes in chronic stroke patients with minor motor symptoms.
• Affected hemisphere is less excitable to produce strong responses.
• At chronic stage, neuronal structure remains disrupted in the affected motor cortex.

ObjectiveTo assess the inter-hemispheric differences in neuronal function and structure of the motor cortex in a small group of chronic stroke patients having suffered a restricted ischemic lesion affecting hand motor representation. GABAergic intracortical inhibition, known to be affected by stroke lesion, was also investigated.MethodsEight patients exhibiting little or no motor impairment were studied using transcranial magnetic stimulation (TMS) and diffusion weighted imaging (DWI) >15 months from diagnosis. Resting motor threshold (MT) for 50 μV and 2 mV motor evoked potentials, and short-interval intracortical inhibition (SICI) were measured from hand muscles. Apparent diffusion coefficients (ADCs) were analyzed from the DWI for the primary motor cortex (M1), the supplementary motor area (SMA) and thalamus for reflecting changes in neuronal organization.ResultsThe MTs did not differ between the affected (AH) and unaffected hemisphere (UH) in 50 μV responses, while the MTs for 2 mV responses were higher (p = 0.018) in AH. SICI was weakened in AH (p = 0.008). ADCs were higher in the affected M1 compared to the unaffected M1 (p = 0.018) while there were no inter-hemispheric differences in SMA or thalamus.ConclusionsInter-hemispheric asymmetry and neuronal organization demonstrated abnormalities in the M1. However, no confident inference can be made whether the observed alterations in neurophysiological and imaging measures have causal role for motor rehabilitation in these patients.SignificanceNeurophysiological changes persist and are detectable using TMS years after stroke even though clinical symptoms have normalized.