The neural bases of limb and oral apraxia: A VLSM study in a cohort of left-hemisphere brain-damaged patients

Introduction : Notwithstanding the high number of experimental studies examining limb and oral apraxia from a clinical, cognitive (Tessari et al., 2004) and neuroimaging point of view, the neural mechanisms underlying this impairment are still little clarified. Motor programming abilities have been recently investigated with f-MRI techniques (Martin et al., 2016) but lesions-to-symptoms mapping is still a fundamental method to underpin the anatomical basis of complex behaviors (Goldenberg et al., 2015). The aim of the present study is to investigate the anatomical basis of ideomotor, ideational, and oral apraxia in a cohort of left-hemisphere brain-damaged patients using the subtraction and voxel-based lesion-symptom mapping (VLSM) localization procedures. Methods : Ideomotor (arm and hand movements vs. finger movements), ideational and oral apraxia were studied through an anatomo-clinical correlative procedure in a sample of 48 left-hemisphere brain-damaged patients. Subtraction and VLSM procedures were used to localize the anatomical bases of these impairments. Results : Lesions of the left supramarginal gyrus and of the left angular gyrus were associated with ideomotor apraxia of the upper limb and hand; lesions of the left supramarginal gyrus and of the left middle frontal gyrus were associated with ideomotor apraxia of finger movement. Ideational apraxia was associated with lesions of the left supramarginal gyrus, left middle frontal gyrus and left inferior frontal gyrus (pars opercularis) suggesting a partial common neural substrate with ideomotor apraxia. A network of left perisylvian areas did emerge as anatomical correlate of oral apraxia, including the left insular cortex, and the left frontal and central opercula, the left inferior frontal gyrus (pars opercularis). Discussion : Our results confirm the existence of relatively independent anatomical specializations in the left hemisphere (Basso et al., 1985; Mengotti et al., 2015), with regards to the hierarchical level of limb apraxia (ideational vs. ideomotor), body parts (upper limb and hand vs. finger movements), and of oral apraxia (Tognola & Vignolo, 1980). References : Goldenberg G. Neuropsychologia (2015) 75: 40-49. Martin M. Brain (2016) 139: 1497-1516. Mengotti P. Neuropsychologia (2015) 79: 256-27