Characterising factors underlying praxis deficits in chronic left hemisphere stroke patients

Rounis, Elisabeth; Halai, Ajay; Pizzamiglio, Gloria; Ralph, Matthew A. Lambon · 2020 · Crossref

DOI: 10.1101/2020.10.16.20213744

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Summary

This study addresses the lack of a unified theoretical account for limb apraxia, a disorder of skilled action common in left hemisphere stroke patients. Traditional models categorize apraxia into "ideational" (conceptual) and "ideomotor" (production) deficits, but these classifications have proven inconsistent due to patient heterogeneity and the co-occurrence of deficits. The authors sought to identify the core latent factors underlying apraxia and their neural correlates using a data-driven approach, challenging the traditional distinction between conceptual and production systems. The researchers tested 41 unselected chronic left hemisphere stroke patients using a comprehensive battery of praxis tasks derived from the Birmingham Cognitive Screen. These tasks included multi-step object use, gesture recognition and production, single object use, meaningless gesture imitation, complex figure copying, and response inhibition (Go/No-Go task). Principal Component Analysis (PCA) was applied to the behavioral data to identify underlying factors. Additionally, a subset of 24 patients underwent structural MRI scanning. The authors employed voxel-based correlational mapping (VBCM), a variant of lesion-symptom mapping, to correlate the PCA-derived factor scores with brain lesion locations, controlling for lesion volume, age, and time post-stroke. The PCA identified three principal components: posture selection, semantic control, and multi-demand sequencing. The VBCM analysis revealed distinct neural correlates for two of these components. The "semantic control" component was associated with lesions in the ventro-dorsal pathway, while the "multi-demand sequencing" component correlated with lesions in both ventral and dorsal pathways. The "posture selection" component showed no significant structural correlates. These findings indicate that apraxia deficits are not strictly divided into ideational or ideomotor categories but rather reflect impairments in specific cognitive processes, including action selection, semantic retrieval, sequencing, and response inhibition. The significance of this work lies in its challenge to the classical Liepmann model of apraxia. By demonstrating that apraxia involves common cognitive functions mapped to specific neural pathways, the study suggests that the disorder is better understood through a framework of domain-general and domain-specific cognitive deficits. This approach provides a more nuanced understanding of the neural basis of apraxia, highlighting the integration of ventral and dorsal streams. The authors conclude that further research using this technique could elucidate the relationship between apraxia and other cognitive disorders, potentially improving diagnostic precision and rehabilitation strategies for stroke patients.

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