Neural bases characterizing chronic and severe upper-limb motor deficits after brain lesion

Chronic and severe upper-limb motor deficits can result from damage to the corticospinal tract. However, it remains unclear what their characteristics are and whether only corticospinal tract damage determines their characteristics. This study aimed to investigate the clinical characteristics and neural bases of chronic and severe upper-limb motor deficits. Motor deficits, including spasticity, of 45 patients with brain lesions were assessed using clinical scales. Regarding their scores, we conducted a principal component analysis that statistically extracted the clinical characteristics as two principal components. Using these principal components, we investigated the neural bases underlying their characteristics through lesion analyses of lesion volume, lesion sites, corticospinal tract, or other regional white-matter integrity. Principal component analysis showed that the clinical characteristics of chronic and severe upper-limb motor deficits could be described as a comprehensive severity and a trade-off relationship between proximal motor functions and wrist/finger spasticity. Lesion analyses revealed that the comprehensive severity was correlated with corticospinal tract integrity, and the trade-off relationship was associated with the integrity of other regional white matter located anterior to the posterior internal capsule, such as the anterior internal capsule. This study indicates that the severity of chronic and severe upper-limb motor deficits can be determined according to the corticospinal tract integrity, and such motor deficits may be further characterized by the integrity of other white matter, where the corticoreticular pathway can pass through, by forming a trade-off relationship where patients have higher proximal motor functions but more severe wrist/finger spasticity, and vice versa.