Interhemispheric structural connectivity underlies motor recovery after stroke

Although ample evidence highlights that the ipsilesional corticospinal tract (CST) plays a crucial role in motor recovery after stroke, studies on cortico-cortical motor connections remain scarce and provide inconclusive results. Given their unique potential to serve as structural reserve enabling motor network reorganization, the question arises whether cortico-cortical connections may facilitate motor control depending on CST damage.

Diffusion spectrum imaging (DSI) and a novel compartment-wise analysis approach were used to quantify structural connectivity between bilateral cortical core motor regions in chronic stroke patients (Fig. 1). Basal and complex motor control were differentially assessed.

Interhemispheric structural connectivity underlies motor recovery after stroke
Figure 1. Cortico-cortical and descending motor network connections. Fiber tracts between core areas of the cortical motor network were created using deterministic fiber tracking based on the HCP1065-template31 in DSI Studio (upper row). Motor tract templates used for anisotropy extraction are depicted as overlays in MRIcroGL (lower row).

Both basal and complex motor performance were correlated with structural connectivity between bilateral premotor areas and ipsilesional primary motor cortex (M1) as well as interhemispheric M1 to M1 connectivity (Fig. 2). Whereas complex motor skills depended on CST integrity, a strong association between M1 to M1 connectivity and basal motor control was observed independent of CST integrity especially in patients who underwent substantial motor recovery. Harnessing the informational wealth of cortico-cortical connectivity facilitated the explanation of both basal and complex motor control.

Interhemispheric structural connectivity underlies motor recovery after stroke
Figure 2. Association between structural motor network connectivity and motor control after stroke. Tractwise anisotropy of several cortico-cortical connections showed a significant association with basal or complex motor control. (A) Correlation coefficients of significant Pearson correlations. (B) Significant partial correlations of cortico-cortical connections with motor behavior when controlling for ilCST damage.

We demonstrate for the first time that distinct aspects of cortical structural reserve enable basal and complex motor control after stroke. In particular, recovery of basal motor control may be supported via an alternative route through contralesional M1 and non-crossing fibers of the contralesional CST. Our findings help to explain previous conflicting interpretations regarding the functional role of the contralesional M1 and highlight the potential of cortico-cortical structural connectivity as a future biomarker for motor recovery post-stroke.

Publication:

Paul, T., Wiemer, V. M., Hensel, L., Cieslak, M., Tscherpel, C., Grefkes, C., Grafton, S. T., Fink, G. R., & Volz, L. J. (2023). Interhemispheric structural connectivity underlies motor recovery after stroke. Annals of Neurology. doi: 10.1002/ana.26737

Correspondence to:

Theresa Paul

Last Modified: 01.08.2023