In Humans, the sense of upright is fundamental reference for bipedal behavior and spatial cognition. Our knowledge of these neural bases is limited to the perception of the vertical in the extrapersonal space (visual vertical, VV). Anatomical correlates of the sense of body upright (postural vertical, PV) are unknown. We identified the polymodal neural bases of sense of upright (VV and PV) in stroke patients, in relation to a mapping of the vestibular cortex.

VV and PV were assessed in 66 first hemisphere stroke patients (58±15 years, 25 F–41 M, 41 right–25 left). Cerebral lesions were reconstructed with MRIcro from patients MRI axial slices (axial AC-PC, T2 flair, 4mm thickness), analyzed by a Voxel Lesion Behavior Mapping statistical approach (VLBM), and compared with a recent meta-analytic mapping of the vestibular cortex.

The VV tilts were contralesional in 45% and ipsilesional in 9% of patients. PV tilts (42%) were always contralesional. Transmodal tilts (PV+VV) were significantly more frequent after right (16/41 patients, 39%) than left lesions (2/25, 8%, Khi²=7.54, P=0.005). Tilts in vertical estimates were more pronounced after right than left lesions for VV (−4.2° vs. −1.7°; t(64)=−2.11; P=0.03) and PV (−5° vs. −0.7°; t(64)=−4.67; P<0.01). In right lesions, polymodal areas of sense of verticality were the inferior parietal cortex, parietal operculum, posterior insula, pre- and postcentral gyri, and the posterolateral thalamus. Only 14% of this core for the sense of verticality overlapped the vestibular areas. In left lesions, the rarity of PV tilts (3 patients) made irrelevant any VLBM analysis.

The operculo-insular cortex and posterolateral thalamus are the core polymodal regions for the human sense of upright, with clear right hemisphere predominance. Surprisingly, the overlap with the vestibular cortex was weak.