The hierarchical organization of human praxis: A lesion-connectome mapping study of limb and oral apraxias

The neural architecture underlying apraxias remains a complex puzzle. While primary motor cortices exhibit clear somatotopic organization, it is unclear whether this segregation extends to the higher-order networks governing skilled actions. Furthermore, the dissociation between verbal (apraxia of speech, AOS) and non-verbal (buccofacial apraxia, BFA) oral motor control remains debated. We investigated the neuroanatomical substrates of limb apraxia (LA), BFA, and AOS in 136 patients with acute left-hemisphere ischemic stroke using voxel-based, region-of-interest-based, and connectome-based lesion-symptom mapping. Our results revealed a fundamental anatomical dissociation extending beyond simple effector specificity. LA was associated with damage to the inferior parietal lobule and widespread white matter disconnections, specifically involving intra-hemispheric temporo-parietal pathways and massive inter-hemispheric transcallosal fibers. In contrast, BFA was attributable to focal cortical lesions centered on the ventral precentral and postcentral gyri, without significant involvement of long-range white matter tracts. AOS showed no significant lesion overlap at the population level, suggesting a highly focal etiology distinct from the premotor patterns of BFA. These findings indicate that LA and BFA differ not only in their effectors but in their network dependency: LA relies on a distributed, bilaterally integrated temporo-parietal network for multimodal action control, whereas BFA depends on localized proprioceptive-motor loops in the ventral sensorimotor cortex. This study provides a structural framework for the hierarchical organization of human praxis, distinguishing between distributed network disconnections and focal cortical dysfunctions.