Nonlinear association between motor impairment after stroke and the contralesional inhibitory deficit

This study investigated the association between upper limb motor impairment (Fugl-Meyer, FM) and transcranial magnetic stimulation (TMS) markers of intracortical inhibition/excitation from the contralesional motor cortex in a large cohort of stroke patients.

A total of 147 S patients was analyzed using transcranial magnetic stimulation (TMS) to measure resting motor threshold, intracortical facilitation, short interval intracortical inhibition (SICI), and cortical silent period. Multiple regression was employed to examine the relationship between these markers and upper limb motor function (FM), adjusting for age, sex, time since stroke, and stroke type. Restricted cubic splines were applied to continuous predictors for modeling potentially nonlinear relationships with the TMS variables.

The study revealed a parabolic/bimodal association between FM and contralesional SICI, when controlling for age, sex, and side of lesion. In patients with severe to moderate impairment, better motor function was associated with less intracortical inhibition, while in patients with moderate to mild impairment the relation is the opposite.

Our results suggest a putative dual role of the contralesional motor cortex in upper limb motor impairment/recovery after stroke.

Contralesional motor cortex SICI, which typically reflects GABA_A activity, might be a relevant biomarker after stroke with a dual signature.