The role of the contralesional primary motor cortex in upper limb recovery after stroke: a scoping review following PRISMA-ScR guidelines.

Background: Stroke often results in motor impairments, with recovery involving complex interactions between the lesioned (ipsilesional) and non-lesioned (contralesional) hemispheres. This scoping review investigates the role of the contralesional primary motor cortex (M1) in motor recovery of the paretic upper limb following stroke, examining its structural and functional changes and compensatory roles.

Methods: A systematic search for scoping review was conducted in PubMed, Embase, Web of Science, and Google Scholar following PRISMA-ScR guidelines. Studies examining contralesional M1 contributions to upper limb recovery in humans and animal models were included. Data were extracted, synthesized qualitatively, and assessed for risk of bias using SYRCLE and Cochrane tools.

Results: A total of 38 studies were included in the analysis, consisting of 34 focused on stroke patients and 4 utilizing animal models. The findings revealed the dual and task-specific role of the contralesional primary motor cortex (M1) in upper limb recovery after stroke. In patients with severe motor impairments, contralesional M1 supported recovery through compensatory mechanisms, such as increased neuronal recruitment and functional reorganization. However, in cases with mild impairments, its activation was associated with inhibitory effects on ipsilesional reorganization, potentially delaying optimal recovery. Animal studies provided evidence of structural and functional plasticity, including dendritic remodeling and enhanced neuronal connectivity, which paralleled improvements in motor function. In human studies, contralesional M1 activation was task-dependent, with pronounced engagement during demanding tasks and unimanual movements. Ipsilateral motor deficits, including reduced dexterity, strength, and coordination, were commonly reported and underscored the disrupted interhemispheric dynamics influencing recovery. Neuromodulation techniques showed promise in modulating interhemispheric interactions and enhancing motor outcomes. These results emphasize the complex interplay between compensatory and inhibitory processes mediated by contralesional M1 in stroke recovery.

Conclusion: The contralesional M1 plays a complex, task-specific role in upper limb recovery after stroke, acting as both a compensatory resource and a potential inhibitory factor. Future research should stratify patients by impairment severity to refine therapeutic approaches.

Clinical trial number: Not applicable.