A cumulative approach to lesion mapping: insights from optic ataxia

Optic ataxia is a rare neuropsychological disorder, characterized by deficits in visually guided reaching movements, typically associated with posterior parietal cortex lesions. From a neuroanatomical standpoint, optic ataxia has been extensively studied, however lesion data remain fragmented in the literature. The present study aim is to address this issue, by implementing a cumulative lesion mapping approach, reconstructing lesions from published cases, using open source softwares like MRIcron and MRIcroGL. The dual objective is to evaluate the reliability of this manual reconstruction approach, while building a dedicated lesion dataset on optic ataxia, useful as a foundation for future research. We selected 14 studies out of 245, with a total of 67 patients with optic ataxia. Lesions were manually copied on a standard brain template, the MNI 152. Ratings from three independent raters were collected on lesion localization, shape and continuity, and inter-rater reliability was assessed through intraclass correlation coefficients, which showed good agreement, supporting consistency of the protocol. Descriptive lesion overlap analysis showed a non-random distribution, with a consistent involvement of bilateral superior and middle occipital gyri, superior and inferior parietal lobules, precuneus and angular gyrus, all regions strongly associated with visuomotor integration. This protocol demonstrated a replicable, low cost approach to lesion mapping, that may serve as foundational tool for future pilot studies. Also, the resulting dataset offers a valuable starting point for upcoming works on optic ataxia. Further developments may include the integration of disconnection analysis to refine our understanding of visuomotor disorders.