From parent-teacher collaboration to young children's numeracy skills: An examination of the underlying mechanisms.

Not all individuals with a neurodegenerative disease, such as Parkinson's disease (PD), experience disease progression in the same way. Some remain clinically stable for years, whereas others exhibit rapid decline despite comparable levels of neuropathology. As early as the late 1980s, Katzman and colleagues reported a striking dissociation between pathological burden and clinical presentation in dementia, emphasizing that neuropathology alone cannot fully account for symptom variability. Since then, converging evidence has shown that cognitive and motor decline vary widely among individuals with similar degrees of neuronal loss. These differences have stimulated growing interest in the concept of resilience, the brain's ability to adapt and maintain function in the face of progressive neurodegeneration. Resilience is commonly described in terms of various forms of reserve, including brain, cognitive, and, more recently, motor reserve. These mechanisms are shaped by lifelong factors such as education, occupational complexity, physical activity, and vascular or genetic risk, all of which influence how pathology and neurodegeneration translate into clinical outcomes. Notably, resilience research has been in the limelight of aging and Alzheimer's disease (AD) research and has only recently received more interest in movement disorders, such as PD. Yet, understanding resilience is increasingly recognized as central to explaining the marked clinical heterogeneity observed in PD. Because certain aspects of resilience (i.e., neural network resources, neuroplasticity) are thought to be build-up over and shaped across the lifespan, it also offers a framework for identifying modifiable protective factors and designing interventions to support long-term functional maintenance. Building on prior conceptual work that introduced a framework for resilience and motor reserve in PD, the present manuscript aims to extend and refine this framework in light of recent empirical and methodological advances. It first revisits the conceptual foundations of cognitive and motor reserve and then critically examines current approaches to quantifying and operationalizing resilience in vivo, highlighting both their potential and their limitations. Building on this, the manuscript delineates how lifestyle-related factors shape the development and modulation of cognitive and motor reserve across the disease course. It further integrates emerging neuroimaging evidence to identify the neurobiological substrates through which these influences manifest. Finally, the manuscript outlines key challenges and future directions for incorporating resilience into neuroimaging research, biological staging models, and personalized intervention strategies for PD.