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The relation between seismic anisotropy and flow-induced deformation in the mantle has the potential to constrain large-scale patterns of mantle dynamics. Anisotropy in the upper mantle has been extensively imaged using a range of seismic data and methods, including shear-wave splitting, receiver functions and surface-wave phase velocities. In the lowermost mantle, the imaging of 3-D anisotropy variations has relied exclusively on shear-wave splitting, resulting in regional constraints. Here, we assess the ability of a different type of seismic data, normal modes, to constrain global-scale mantle anisotropy, focusing on azimuthal anisotropy in the lowermost mantle. Normal modes are whole Earth oscillations that are induced by large earthquakes and have sensitivity to large-scale elastic structure throughout the entire Earth. Normal-mode splitting functions have previously been used to infer azimuthal anisotropy …